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Car Forum / Honda Cars / September 2005Terrible Fuel-Efficiency - 2003 Accord
Hey guys, I just purchased a 2003 Honda Accord LX Sedan Automatic and moved to Colorado Springs. Loaded down with all of my personal belongings, I got 32mpg during the 770 mile drive from Dallas. This was fine with me. During the first few weeks that I was here, my driving was evenly split between city, small highway (55mph) and mountain driving. I averaged 24mpg. Determined to do better, I committed to keep the TAC under 3,000 for the entire volume of gas in the newly-filled tank. I just filled it up last night and did the calculation. 22mpg. My eyes are crossing... Almost all of my driving for this past tank has been city driving. I have not been an A/C fiend, and I shift into Neutral and coast downhill rather than let the engine do it. I take my time getting places and I don't jackrabbit starts or stops. What am I doing wrong? Or does Colorado just suck? Is my expectation of 25mpg city driving unreasonable? > What am I doing wrong? Or does Colorado just suck? Is my expectation > of 25mpg city driving unreasonable? Yes it is, especially considering your altitude and mountainous terrain. EPA estimates on the V-6 Accord are 21 city, 30 highway. In your driving conditions, anything over the EPA city number is a good result for city driving. John > Drewaffe wrote: > > > What am I doing wrong? Or does Colorado just suck? Is my expectation > > of 25mpg city driving unreasonable? > > Yes it is, especially considering your altitude and mountainous terrain. The altitude should not affect mileage. (Empirical evidence of this is my 91 Civic: Got 40 mpg at sea level for several months. Still getting 40 mpg at a mile high altitude, late spring through fall.) Driving in mountainous terrain may be the problem. The car is two years old, though. It is about due for a tuneup. Have you had one done recently? Check your owner's manual. It may specify new fuel filter air filter plugs at a minimum. > EPA estimates on the V-6 Accord are 21 city, 30 highway. I only know that the regular unlead gas is 86 instead of 87 in Utah and Colorado. I do not know that affects the gas mileage, also. > > What am I doing wrong? Or does Colorado just suck? Is my expectation > > of 25mpg city driving unreasonable? [quoted text clipped - 6 lines] > > John See, among others, http://www.valvoline.com/carcare/articleviewer.asp?pg=dsm20020401go&cccid=3& scccid=3 . http://www.idavette.net/hib/fuel/ The lower octane gas in the Rocky Mountain states is appropriate for the altitude. I doubt the lower octane affects fuel mileage. > I only know that the regular unlead gas is 86 instead of 87 in Utah and > Colorado. I do not know that affects the gas mileage, also. [quoted text clipped - 11 lines] > > > > John > The lower octane gas in the Rocky Mountain states is appropriate for the > altitude. I hadn't considered that. The altitude has the same effect as not opening the throttle all the way, so lower octane works fine. Mike <SNIP> I shift into Neutral and coast downhill > rather than let the engine do it. ---------------------------- It's illegal to shift into neutral when going downhill, in some juristictions. It's for a couple of good reasons. Don't do it. 'Curly' ><SNIP> I shift into Neutral and coast downhill >> rather than let the engine do it. >---------------------------- > >It's illegal to shift into neutral when going downhill, in some >juristictions. It's for a couple of good reasons. Don't do it. And prey tell what ARE those reasons. >'Curly' Waiving the right to remain silent, flobert <nomail@here.NOT> said: >><SNIP> I shift into Neutral and coast downhill >>> rather than let the engine do it. [quoted text clipped - 4 lines] > > And prey tell what ARE those reasons. Much of the speed reduction when going downhill is achieved by taking your foot off the gas and letting the engine do the "brake" work. By putting the transmisison in neutral, you have to rely entirely on your braking system, risking rapid overheating of the brakes. Overheated brakes work very poorly, leaving you open to destruction.  SignatureLarry J. - Remove spamtrap in ALLCAPS to e-mail The United States is the greatest country in the world..! Twenty-five million illegal aliens can't be wrong. > Waiving the right to remain silent, flobert <nomail@here.NOT> said: > [quoted text clipped - 14 lines] > your braking system, risking rapid overheating of the brakes. > Overheated brakes work very poorly, leaving you open to destruction. apart from the very obvious danger of what you describe, coasting in neutral also /raises/ gas consumption on an injected car. if the ecu sees no throttle above a certain rev, it assumes coasting mode and shuts off gas delivery entirely. it won't do that if it's idling because the revs aren't high enough to register as a coast. coasting in neutral could arguably save gas on a carburetted engine so that's probably where this bad practice arose, but for injected engines, absolutely leave it in gear all the time. > > Waiving the right to remain silent, flobert <nomail@here.NOT> said: > > [quoted text clipped - 24 lines] > that's probably where this bad practice arose, but for injected engines, > absolutely leave it in gear all the time. Hello, Great post. I just wanted to add that it's a bad habit to get into. I doubt that it saves any gasoline. In addition, it adds more "wear" to the transmission. In other words, your transmission will wear out quicker if you shift into neutral every time you go downhill. Jason SignatureNEWSGROUP SUBSCRIBERS MOTTO We respect those subscribers that ask for advice or provide advice. We do NOT respect the subscribers that enjoy criticizing people. >Hello, >Great post. I just wanted to add that it's a bad habit to get into. I >doubt that it saves any gasoline. In addition, it adds more "wear" to the >transmission. In other words, your transmission will wear out quicker if >you shift into neutral every time you go downhill. >Jason We've just had a past that states it saves on carb cars, but not, generally, fuel injected ones, which you obviously didn't read - despite the fact that the poster only considered immediate consumption, and not the increased downhill speeds and its implications if the coast is continued on the flat or near-flat areas following the slope. I'm intrigued though, by your asertation that being in neutral puts INCREASED wear on a transmission, since it was my understanding that since it would ahve no load, and not be spun beyond the rated ranges (in all probability slowly, depending on gearbox design), that it wouldn't increase wear, but instead decrease it. >>Hello, >>Great post. I just wanted to add that it's a bad habit to get into. I [quoted text clipped - 15 lines] > (in all probability slowly, depending on gearbox design), that it > wouldn't increase wear, but instead decrease it. for the clutch packs, slipping in & out of neutral is more use than they would experience in coasting, hence it can cause more wear. less of a deal on the honda, and completely irrelevent in the face of the safety arguments however! either way, there's no justification for coasting in neutral. >Waiving the right to remain silent, flobert <nomail@here.NOT> said: > [quoted text clipped - 12 lines] >your braking system, risking rapid overheating of the brakes. >Overheated brakes work very poorly, leaving you open to destruction. Whilst yes, that was the case in the 60s, not since the late 70s at the latest has this even been an issue. A semi, comming down a mountain, yes, a car down a hill, no. Keep with the times, and stop with the decades old misinformation please. >>Waiving the right to remain silent, flobert <nomail@here.NOT> said: >> [quoted text clipped - 19 lines] > mountain, yes, a car down a hill, no. Keep with the times, and stop > with the decades old misinformation please. it's not misinformation, it's dead accurate. brakes linings /do/ over heat, brake lines fail, brake fluids boil, speeds can become excessive, and you are not in full control of the vehicle in the event you need to make any evasive manoevers. it's bad for the transmission too. do not ever coast in neutral down a hill! /EVER/! Waiving the right to remain silent, jim beam <nospam@example.net> said: > it's not misinformation, it's dead accurate. brakes linings > /do/ over heat, brake lines fail, brake fluids boil, speeds can > become excessive, and you are not in full control of the vehicle > in the event you need to make any evasive manoevers. it's bad > for the transmission too. do not ever coast in neutral down a > hill! /EVER/! Somtimes, nothing will convince a zealot. Like the constant debate wiht those who still think they're doing their new cars a favor by changing the oil every 3,000 miles. SignatureLarry J. - Remove spamtrap in ALLCAPS to e-mail The United States is the greatest country in the world..! Eleven million illegal aliens can't be wrong. > Waiving the right to remain silent, jim beam <nospam@example.net> > said: [quoted text clipped - 9 lines] > wiht those who still think they're doing their new cars a favor by > changing the oil every 3,000 miles. good comparison! but here's the difference: i don't care if he wastes his money on excessive oil changes. really. i /do/ however care if his willful ignorance affects /my/ safety on the road. if he careens out of control onto /my/ side of the freeway and hits /my/ car because he's been coasting in neutral and has lost control because his brakes are toasted, he'd better make sure he can run faster than me, because i /will/ be upset. Waiving the right to remain silent, jim beam <nospam@example.net> said: >> Waiving the right to remain silent, jim beam >> <nospam@example.net> said: [quoted text clipped - 17 lines] > and has lost control because his brakes are toasted, he'd better > make sure he can run faster than me, because i /will/ be upset. Hahaha..! Agreed. SignatureLarry J. - Remove spamtrap in ALLCAPS to e-mail The United States is the greatest country in the world..! Eleven million illegal aliens can't be wrong. >>>Waiving the right to remain silent, flobert <nomail@here.NOT> said: >>> [quoted text clipped - 25 lines] >make any evasive manoevers. it's bad for the transmission too. do not >ever coast in neutral down a hill! /EVER/! For this to work as you say, you'd need the following to happen badly ventilated/cooled brakes. constant application of brakes weakened brake lines under-spec brake fluid Any of these would occur in any sudden deceleration from a high speed (such as an emergency stop on the highway) and be in all probablility more fatel then. Modern brakes are designed to cope with small aplication loads for longer periods of time. Many car manufacturers do these kinds of manouvers as tests in their brake systems, to prevent precisely this from happening. /whats more, its the very first fade test. Were you then to take the car on a long winding downhill run from the mountains you'd have a lot more heat buildup in your brakes, and a lot greater application of wear, having heaier repeated applications of the brakes, with a lower ventilation speed. You're also on the assumption tha when coasting, people ride the brake instead. you know, i've never done that. if i coast, i don't then ride the brake, instead i'll make a check application, every so often. As for the 'not in full control' argument, again, thats from the 50's and 60's before the advent of the nice modern synchromesh. For an avoidance measure, engine power or no will make no difference. For stopping, your braking speed is limitedby the static friction lmiit of the vehicles tyres. In fact, you're not having to brake the rotational inertia of the engine and connected gearbox componants, so you're ahead there too. The only way i can see the engine being of any benefit is if you ahve to go FASTER, or a 90dergee+ oversteer situation, but in that case, you'd probably want to change from a cruising gear in any case. Regardless, I'm sure we'll be able to go around in circles like this, each counter-claiming the other. Instead, i'll send an email over to see if Mythbusters will take a look at it. >>>>Waiving the right to remain silent, flobert <nomail@here.NOT> said: >>>> [quoted text clipped - 31 lines] > weakened brake lines > under-spec brake fluid 1. all brakes heat on application. that's fundamental fact. if you're dissipating /all/ your forward energy through the brakes and are not using engine braking because you are in neutral, the brakes will heat more!!! that's fact!!! 2. you can easily have constant application of brakes. you're never going to have road conditions that just happen to suit you! 3. brake lines deteriorate with age! fact. 4. brake fluid absorbs water from the air. it starts to degrade the moment you open the bottle. fact. > Any of these would occur in any sudden deceleration from a high speed > (such as an emergency stop on the highway) and be in all probablility > more fatel then. that's stupid. > Modern brakes are designed to cope with small aplication loads for > longer periods of time. Many car manufacturers do these kinds of [quoted text clipped - 4 lines] > application of wear, having heaier repeated applications of the > brakes, with a lower ventilation speed. you don't know what you're talking about. any brake fades as a function of temperature. temperature is a function of the speed you want to turn into kinetic energy. any form of stop start driving, regardless of hills, heats brakes. period. > You're also on the assumption tha when coasting, people ride the brake > instead. you know, i've never done that. if i coast, i don't then ride > the brake, instead i'll make a check application, every so often. dude, apart from the fact that coasting is illegal, you're also indicating you don't have the vehicle under proper control. > As for the 'not in full control' argument, again, thats from the 50's > and 60's before the advent of the nice modern synchromesh. eh? what has synchromesh got to do with it? that's utterly irrelevant. > For an > avoidance measure, engine power or no will make no difference. but engine braking does!!! that's why automatics down-shift - for engine braking and safety. > For > stopping, your braking speed is limitedby the static friction lmiit of > the vehicles tyres. only if the brakes can supply sufficient friction. if they're toast, you can have the best tires in the world, but they won't mean a damned thing to stop you running into that kid that's just kicked their ball into the road. > In fact, you're not having to brake the rotational > inertia of the engine and connected gearbox componants, so you're > ahead there too. what planet are you on??? look up engine braking on google. truck manufacturers invest millions in engine braking technology because its so effective AND SAFE BECAUSE IT DOESN'T OVERHEAT BRAKES. > The only way i can see the engine being of any > benefit is if you ahve to go FASTER, or a 90dergee+ oversteer > situation, but in that case, you'd probably want to change from a > cruising gear in any case. eh? > Regardless, I'm sure we'll be able to go around in circles like this, > each counter-claiming the other. Instead, i'll send an email over to > see if Mythbusters will take a look at it. be my guest. geeze. i can maybe understand ignorance as an excuse if the engineering is not understood, but using it as an excuse against the law??? buddy, you take the prize! On 8/20/2005 2:34 PM jim beam spake these words of knowledge: >>>>>Waiving the right to remain silent, flobert <nomail@here.NOT> said: >>>>> [quoted text clipped - 34 lines] > using engine braking because you are in neutral, the brakes will heat > more!!! that's fact!!! No; the *fact* is, braking will generate more heat. If that heat is dissipated in some other, controlled manner, the brakes will not be any hotter. > 2. you can easily have constant application of brakes. you're never > going to have road conditions that just happen to suit you! [quoted text clipped - 9 lines] > > that's stupid. I don't know what flobert is talking about here either. >> Modern brakes are designed to cope with small aplication loads for >> longer periods of time. Many car manufacturers do these kinds of [quoted text clipped - 9 lines] > into kinetic energy. any form of stop start driving, regardless of > hills, heats brakes. period. The kinetic energy is the car in motion. The conversion desired is from kinetic energy to heat energy. I think you know this, but that's not how your paragraph read. Any form of braking heats brakes, period. The point made was that the incline adds to kinetic energy being overcome by the brakes. This is entirely correct, but your note indicates that gravity is irrelevant as a contributor. Again, I think you know this, but your paragraph doesn't indicate it. >> You're also on the assumption tha when coasting, people ride the brake >> instead. you know, i've never done that. if i coast, i don't then ride >> the brake, instead i'll make a check application, every so often. > > dude, apart from the fact that coasting is illegal, you're also > indicating you don't have the vehicle under proper control. Even if you are in a place where the local populace has enacted some statute, your blanket statement is wrong. For it to be correct in the United States, it would have to be a federal statute. It is not. To me, it sounds like the old canard we heard when we were kids, that it was illegal to drive your car barefoot. It what respect is the vehicle not under proper control? Granting that if it's moving, it *may* not be under proper control, I don't see that coasting automatically means it is not. >> As for the 'not in full control' argument, again, thats from the 50's >> and 60's before the advent of the nice modern synchromesh. > > eh? what has synchromesh got to do with it? that's utterly irrelevant. I agree. I don't understand this at all. >> For an >> avoidance measure, engine power or no will make no difference. [quoted text clipped - 18 lines] > manufacturers invest millions in engine braking technology because its > so effective AND SAFE BECAUSE IT DOESN'T OVERHEAT BRAKES. Apples and oranges here, Jim. The truck has a great deal more weight (and therefore kinetic energy) to overcome at any given time, and the typical over-the-road truck is driven anywhere from 5 to 20 times as many miles over its lifetime. >> The only way i can see the engine being of any >> benefit is if you ahve to go FASTER, or a 90dergee+ oversteer >> situation, but in that case, you'd probably want to change from a >> cruising gear in any case. > > eh? I don't get this either. >> Regardless, I'm sure we'll be able to go around in circles like this, >> each counter-claiming the other. Instead, i'll send an email over to [quoted text clipped - 3 lines] > the engineering is not understood, but using it as an excuse against the > law??? buddy, you take the prize! Please tell me what law you're speaking of, and what jurisdiction you're referring to. There is no such reference in the US Code (federal law). Although I've found one place that indicates that there is such a law in British Columbia, that forum points out that each province makes its own laws. I found a reference to a California law and a Texas law as well, so wherever this guy is (looks like Florida), he may be covered, he may not. In either event, simply saying coasting is illegal generally is incorrect. RFT!!! Dave Kelsen Signature... At dinner yesterday, I tried to cut myself a slice of prime rib, but it was only divisible by itself and one. >>>>>Waiving the right to remain silent, flobert <nomail@here.NOT> said: >>>>> [quoted text clipped - 36 lines] >using engine braking because you are in neutral, the brakes will heat >more!!! that's fact!!! I'm not arguing that the brakes will generate more heat. I did not at any time say that. however, brake fading is only an issue in modern brakes if the temperature goes over a certain temperature. The amount of fade, and the temperature at which it occurs is variable depending on the brake type/composition. For instance, brakes in a Formula 1 car INCREASE in braking abaility as they get hotter, until they actually burn. there is virtually no fade. They get hot, they get better, they get too hot, they burn, they dissapear, but it takes a GREAT deal of heat to burn the,. I saw some test figures from the development of the Lotus Elise some 10 years ago. They tested the vehicle on an extreme downhill section of the Alps, at racing constions, and found less than 1% fade. Those are two clear examples that countradict your blanket assertions. Modern brakes do not decrease in retardation ability in direct relationship to their temperature, and haven't for many years. >2. you can easily have constant application of brakes. you're never >going to have road conditions that just happen to suit you! So, i can't pick when i'm going to coast? My gearbox has a life of its own? What it seems you fail to distinguish here is the difference between coasting on ALL slopes, regardless of grade, and only doing so where needed. I will give you two examples from here in Georgia - thers a series of hills on US19 betwen thomaston and zebulan, they're not steep gradients, and quite long, i will often coast down them. no brakes needed, except for the occasioanl momentary check-brake as my speed rises too high (the southmost slope is by the county line, and often deputies will hide there checking for speeders). The second example is a hill much further north - Barnes Mill Road, in Marietta (just off the 120 loop by exit 265 of I75) a much steeper slope, of about 1 mile in length, where not only do you keep it in gear, but have to use your brakes over aout 40% of it. Gradent of the second is about double that of the first. no-one is suggesting its an 'all or nothing', and i for one certainly haven't. its you that suggesting that in all situations, in all circumstances, you're risking life and limb >3. brake lines deteriorate with age! fact. Certainly, and if a brake line was to go, it'd be more likely under the greater heat and pressure of a high speed emergency deceleration, than under a gentle coasting, where the brakes may or may not be used at all, see above. >4. brake fluid absorbs water from the air. it starts to degrade the >moment you open the bottle. fact. I don't know about you, but i would call brake fluid with heavy water contamination to be 'under spec' >> Any of these would occur in any sudden deceleration from a high speed >> (such as an emergency stop on the highway) and be in all probablility >> more fatel then. > >that's stupid. Whats stupid? The forces and energies invloved in any high speed sudden deceleration are much more severe on a vehicle's braking system, than, as you're suggesting, lightly riding them for a mile or two. >> Modern brakes are designed to cope with small aplication loads for >> longer periods of time. Many car manufacturers do these kinds of [quoted text clipped - 9 lines] >into kinetic energy. any form of stop start driving, regardless of >hills, heats brakes. period. fraid not. go look up some test results, there is no direct corrolation between fade and temperature on modern brakes. no straight line graph that starts with retardation ability being at max when the temperature is some 'cold point' that we should take to be air ambent temp, with retardation ability dropping in direct response to temperature increase. There is instead a gradual decrease from the brak systems optimal temperature (whichis NOT air ambient) to the 'max operating' and then a more rapid decrease. >> You're also on the assumption tha when coasting, people ride the brake >> instead. you know, i've never done that. if i coast, i don't then ride >> the brake, instead i'll make a check application, every so often. > >dude, apart from the fact that coasting is illegal, you're also >indicating you don't have the vehicle under proper control. I asked a friend (a deputy in the next county) and he's never heard of any such law here. Another fact in error/ >> As for the 'not in full control' argument, again, thats from the 50's >> and 60's before the advent of the nice modern synchromesh. > >eh? what has synchromesh got to do with it? that's utterly irrelevant. prior to the synchromesh, when changing gear, entering a gear etc. - it was neccesary to adjust the engine speed to match, to select the gear, and so on. with a synchromesh, its easy to put the car in any gear suitable for the speed of the vehicle. That was the basis of the original 'loss of control' arguments - you had no near-immediate ability to recouple the engine to the wheels. >> For an >> avoidance measure, engine power or no will make no difference. > >but engine braking does!!! that's why automatics down-shift - for >engine braking and safety. how does engine braking work to increase safety? >> For >> stopping, your braking speed is limitedby the static friction lmiit of [quoted text clipped - 4 lines] >thing to stop you running into that kid that's just kicked their ball >into the road. ok, so let me get your argument straight. engine braking is required because its unsafe to coast. Its unsafe to coast because everyone that does so, does so with badly adjusted and maintained brakes, and insists on riding those brakes to the point of failure whilst coasting. thus when there is an emergency, the small engine retardation effect is then VITAL to stop the car. I did some tests this adrernoon, using two automatic vehicles, using an old airstrip here. I weighted things in your favour, by using older vehicles (which would have brakes more liekly to fade, and have worn brake systems - a 87 caravan, and an 88 civic. one big car, one little car. Unfortunatly, both are automatics, but on the upside, they have drum brakes with cable-operated handbrakes. I used a speed of 50mph, and attempted a stoping manouver with ONLY engine braking, so as to measure the braking distance, which can then be compaired to a standaised figure, such as ohh, the UK DOT standard braking distances (http://www.highwaycode.gov.uk/09.htm at the bottom) the civic with its 4speed autom box, with me manually downshifting managed to slow to 8mph in 450ft, and wouldn't slow any further. on the second run, engaging the handbrake at 20mph reduced the vehicle to 8mph in 420ft and to a stop in 460. The caravan, with a 3lv6, and 3sp auto, slowed to 9mph in 390ft, and stopped in 430ft with the handbrake application. (well, foot activated parking brake) by constrast, the UK figures show the braking distance to be a total of 120ft, INCLUDING THINKING DISTANCE - not a factor since it was a pre-planned stop point. so, 125ft is the actual stopping distance. so its more than 3x as bad. It gets worse though, since the vehicle used in the uk govt. figures is a 1964 ford Anglia - a car not noted for its agility, and which had a braking system marginally better than a foot operated wooden block pressed to each wheel. Modern cars and SUVs achieve braking distances almost half that. Both vehicles managed a standard braking distance of around 100ft (repeated many times - both with and withouth being in gear) >> In fact, you're not having to brake the rotational >> inertia of the engine and connected gearbox componants, so you're [quoted text clipped - 10 lines] > >eh? whats 'eh' about it. The only way the addition of engine power can assist in any incident is if you are in a spin, or in a situation where you would be required to go faster. In any other case, the car being in gear would no be of any consequence, or positive benefit. >> Regardless, I'm sure we'll be able to go around in circles like this, >> each counter-claiming the other. Instead, i'll send an email over to [quoted text clipped - 3 lines] >the engineering is not understood, but using it as an excuse against the >law??? buddy, you take the prize! Ignorance of engineering is, apprantly, your forte. As is indeed ignorance of the law. If it was so illegal, why did Saab in the 70s sell vehicles that were despigned to freewheel down hills without having to take the car out of gear, you only had to pull a lever i think it was. It was discontinued mainly because most drivers didn't use it, and felt uncomfortable when they did, mainly due to the commonly held misconception you share. This, like any long term myth, is one that clearly won't go away after having being delt with in common sense. In short, you say that if you coast down any hill, you must coast down all (can't pick your situation, as you call it) and you must ride your brakes at al times. Oh, and you have an old brake system, that's been poorly maintained, so they would fade to nothing (despite the fact it would fail at the 50mph braking test above, due to the greater heat generation vs dissipation, on your straight-line temp-retardation graph) and that in an emergency, a braking system that has no effect on actual deceleration under proper braking, and which has very poor deceleration figures when used on its own is not only usefull, but legally required to be used. Would you care to attempt to refute these facts, maybe do some measurements of your own with your own vehicles. Maybe even employ some simple logic. >>>>>>Waiving the right to remain silent, flobert <nomail@here.NOT> said: >>>>>> [quoted text clipped - 46 lines] > get too hot, they burn, they dissapear, but it takes a GREAT deal of > heat to burn the,. those are carbon fiber brakes. they're banned for road use and for motorcycle track use. different materials behave different. the materials we're discussing here, cast iron brake disks and carbon/aramid fiber/ceramic/metal pad composites do not exhibit those characteristics. they progressively fade as temperature rises. certain formulations used on racing/performance cars fade less at high temperatures, and oem honda pads are better than many after-market ones, but they all still fade. citing an illegal unobtainable exotic is clutching at straws. > I saw some test figures from the development of the Lotus Elise some > 10 years ago. They tested the vehicle on an extreme downhill section > of the Alps, at racing constions, and found less than 1% fade. Those > are two clear examples that countradict your blanket assertions. > Modern brakes do not decrease in retardation ability in direct > relationship to their temperature, and haven't for many years. dude, i used to live in san francisco. and i still work there. have you ever driven down filbert st hill from broadway to lombard, stopping at every stop sign? using a crappy set of aftermarket brake pads that fade like mfsob's? i have. don't talk to me about brake fade being a thing of the past. >>2. you can easily have constant application of brakes. you're never >>going to have road conditions that just happen to suit you! > > So, i can't pick when i'm going to coast? My gearbox has a life of its > own? not legally, no. how many times do you need to be told? if you have an accident and the cops investigate, they'll throw the book at you. assuming you don't run into me of course, in which case the cops would be the least of your concerns. > What it seems you fail to distinguish here is the difference between > coasting on ALL slopes, regardless of grade, and only doing so where [quoted text clipped - 12 lines] > that in all situations, in all circumstances, you're risking life and > limb 1. so you waste gas because your fuel injected car /is/ injecting gas while you're idling not engine braking 2. you don't have the vehicle under full control /and/ 3. you're using brakes where you needn't? wow, how did nasa ever miss the opportunity of hiring you? >>3. brake lines deteriorate with age! fact. > > Certainly, and if a brake line was to go, it'd be more likely under > the greater heat and pressure of a high speed emergency deceleration, > than under a gentle coasting, where the brakes may or may not be used > at all, see above. but dude, you're using the brakes /more/ when coasting in neutral!!! >>4. brake fluid absorbs water from the air. it starts to degrade the >>moment you open the bottle. fact. > > I don't know about you, but i would call brake fluid with heavy water > contamination to be 'under spec' water absorbtion means lowers boiling point. excess brake use approaches the boiling point of a contaminated system more quickly!!! >>>Any of these would occur in any sudden deceleration from a high speed >>>(such as an emergency stop on the highway) and be in all probablility [quoted text clipped - 6 lines] > system, than, as you're suggesting, lightly riding them for a mile or > two. eh? of course! but the energy you can absorb by braking is a function of the available temperature delta. if the initial temperature is already high because you've been riding the brakes, the available delta is less. it that hard to understand? >>>Modern brakes are designed to cope with small aplication loads for >>>longer periods of time. Many car manufacturers do these kinds of [quoted text clipped - 12 lines] > fraid not. go look up some test results, there is no direct > corrolation between fade and temperature on modern brakes. rubbish. > no straight > line graph that starts with retardation ability being at max when the > temperature is some 'cold point' that we should take to be air ambent > temp, with retardation ability dropping in direct response to > temperature increase. dude, you're turning speed into heat. if the brakes fade more as the temperature rises, and they do, you want the initial temperature to me minimized. > There is instead a gradual decrease from the > brak systems optimal temperature (whichis NOT air ambient) to the 'max > operating' and then a more rapid decrease. so what is "optimal" for a normal car braking system??? and there's no physical way brake temperature can decrease if you're dumping kinetic energy into them. >>>You're also on the assumption tha when coasting, people ride the brake >>>instead. you know, i've never done that. if i coast, i don't then ride [quoted text clipped - 5 lines] > I asked a friend (a deputy in the next county) and he's never heard of > any such law here. Another fact in error/ california vehicle code #21710. "Coasting Prohibited. The driver of a motor vehicle when traveling on down grade upon any highway shall not coast with the gears of such vehicle in neutral." >>>As for the 'not in full control' argument, again, thats from the 50's >>>and 60's before the advent of the nice modern synchromesh. [quoted text clipped - 7 lines] > original 'loss of control' arguments - you had no near-immediate > ability to recouple the engine to the wheels. rubbish. if you can't get the vehicle into gear, whether it's automatic or stick, synchro or not [i've driven non-synchro transmissions and there's no reason you can't shift if you double-clutch] then either you're not competent or the vehicle is defective and shouldn't be on the road. again, synchro is irrelevant. >>>For an >>>avoidance measure, engine power or no will make no difference. [quoted text clipped - 3 lines] > > how does engine braking work to increase safety? because, as mentioned so many times before, it takes a substantial load off the brakes!!! it also allows you to instantly re-power the vehicle if required. >>>For >>>stopping, your braking speed is limitedby the static friction lmiit of [quoted text clipped - 11 lines] > coasting. thus when there is an emergency, the small engine > retardation effect is then VITAL to stop the car. no, it's necessary to keep the brakes cool for maximum stopping power. remember the temperature delta thing??? > I did some tests this adrernoon, using two automatic vehicles, using > an old airstrip here. I weighted things in your favour, by using older [quoted text clipped - 26 lines] > standard braking distance of around 100ft (repeated many times - both > with and withouth being in gear) dude, the engine does not /stop/ the car [unless you turn off the ignition]. but it does offer braking in proportion to engine speed [which is why you downshift when engine braking] and yet again, this reduces the thermal load on the brakes. that's why cars with automatic transmissions, like honda, detect when the car is braking and down-shift to increase engine braking. i guess you'd never notice that if you habitually coast in neutral, but it's fact nevertheless. >>>In fact, you're not having to brake the rotational >>>inertia of the engine and connected gearbox componants, so you're [quoted text clipped - 15 lines] > where you would be required to go faster. In any other case, the car > being in gear would no be of any consequence, or positive benefit. so these situations never occur? you should know that it does rain occasionally... >>>Regardless, I'm sure we'll be able to go around in circles like this, >>>each counter-claiming the other. Instead, i'll send an email over to [quoted text clipped - 11 lines] > use it, and felt uncomfortable when they did, mainly due to the > commonly held misconception you share. well, funky cv transmissioned daf's & volvos had a button that /increased/ engine braking for downhill situations. one of these situations does not compute. > This, like any long term myth, is one that clearly won't go away after > having being delt with in common sense. In short, you say that if you > coast down any hill, you must coast down all (can't pick your > situation, as you call it) and you must ride your brakes at al times. you're the guy riding brakes. i use the engine. > Oh, and you have an old brake system, that's been poorly maintained, > so they would fade to nothing (despite the fact it would fail at the [quoted text clipped - 6 lines] > facts, maybe do some measurements of your own with your own vehicles. > Maybe even employ some simple logic. no. you're using twisted logic to put utterly incorrect words in my mouth. the physics are very simple: a brake turns kinetic energy into heat. as the temperature rises, the ability to continue turning k.e. into heat falls. let me know if you can grasp that concept, then we can continue this discussion. >>>>>>>Waiving the right to remain silent, flobert <nomail@here.NOT> said: >>>>>>> [quoted text clipped - 55 lines] >honda pads are better than many after-market ones, but they all still >fade. citing an illegal unobtainable exotic is clutching at straws. One of those was an 'exotic', but the brakes on an elise is fully road legal - hell, they were designed and developed in the US, in California actually - I'll dig out the manufacturers name if you want. I could go and retrofit a set onto my civic or caravan any time I wanted. I'd love if you could cite me a make, and manufacturer of a brake system that had its optimal braking temperature at room temp. Any type of vehicle will do, as long as its a powered braking system (no bicycles) >> I saw some test figures from the development of the Lotus Elise some >> 10 years ago. They tested the vehicle on an extreme downhill section [quoted text clipped - 8 lines] >fade like mfsob's? i have. don't talk to me about brake fade being a >thing of the past. Its been about 5 years since i was in san fransisco last (i used to work on contract for a company, having to drive to, from, around SF all day long, as well as oakland, sausalito, and yerba buena/treasure island. i think i only drove over the hill once, usually i take the tunnel, california street was it? all i remember is driving from the bay bridge to the GG bridge, i drove past the strip clubs, througha tunnel, and then joined up with lombard about 3 streets over. First time i ever drove in America, back then, and the first time i'd ever driven an automatic on the roads. From what i remmeber, though, the hills weren't that bad. I id much heavier testing and laoding of my brakes, i had no fade problems. It sounds like you need to take better care of your brake system. Use adequately rated parts, not any old crap you can find. >>>2. you can easily have constant application of brakes. you're never >>>going to have road conditions that just happen to suit you! [quoted text clipped - 6 lines] >assuming you don't run into me of course, in which case the cops would >be the least of your concerns. You ahve strange definitions of whats legal and whats not. You believe that if its illegal in californai, it is everywhere. Its not, as far as i, and the law enforcment personnel i have questioned, illegal here, where i am, therefore they would NOT throw the book at me. nor was it, or is it illegal in the UK - its not reccomended there, but then neither is crossing your arms on the wheel - the action is not 'citeable'. No action can be taken. In other words, it is legal. Do it during your driving test, and you will get a minor error, not even an immediate failing error. >> What it seems you fail to distinguish here is the difference between >> coasting on ALL slopes, regardless of grade, and only doing so where [quoted text clipped - 15 lines] >1. so you waste gas because your fuel injected car /is/ injecting gas >while you're idling not engine braking but i then save it due to the increased momentum when i come to the next incline - i need to accelerate later. See later for actual figures. >2. you don't have the vehicle under full control /and/ still not sold me on this 'full control' thing. I've given two situations, the ONLY two me and the deputy mentioned further down could think of. >3. you're using brakes where you needn't? when am i doing that. repeatedly told you, i don't ride the brakes as part of coasting. I allow the vehicles momentum to increase - thats half the point. whats the point of concerving the energy of memntum by not dumping it in the engine, if you're gong to dump it into the brakes instead? >wow, how did nasa ever miss the opportunity of hiring you? by me not having applied. Friends already work there, and i've heard too many bad stories about what moral,a nd the structure and work situation is like. >>>3. brake lines deteriorate with age! fact. >> [quoted text clipped - 4 lines] > >but dude, you're using the brakes /more/ when coasting in neutral!!! not really. depends on the hill, the situation, my speed, the speed of the vehicles around me, and a few other facts under my control. As i noted previously, on the hills i coasted down (LEGALLY) yesterday, the brakes were not used at all, and the engine was not put back into gear until a mile after the last hill, when my speed 'boost' from coasting had diminished. >>>4. brake fluid absorbs water from the air. it starts to degrade the >>>moment you open the bottle. fact. [quoted text clipped - 4 lines] >water absorbtion means lowers boiling point. excess brake use >approaches the boiling point of a contaminated system more quickly!!! yes, and a contaminated system is one which has obviously not been taken care of. Such fluid would boil, and thus make the car fail under any severe braking condition. It is thus underspecification, and dangerous. Any brake fluid this highly contaminated with water should already ahve been changed. >>>>Any of these would occur in any sudden deceleration from a high speed >>>>(such as an emergency stop on the highway) and be in all probablility [quoted text clipped - 11 lines] >already high because you've been riding the brakes, the available delta >is less. it that hard to understand? again, you have this assumption, this ERONOIUS assumption, that 1) you are not using the engine to check the speed thus 2) you MUST be using the brakes to perform the same action. the problem, that you seem to have trouble accepting is that *shock horror* 2 does not follow from 1. performing action number 1 does NOT require action number 2 to be followed. Instead of riding my brakes, checking my speed, I LET MY SPEED INCREASE. the amount is usually 5-9mph, but it is momentum which keeps me going on the flat at a speed and for a distance that would require me to re-engage the transmission, and power my engine, meaning it runs on fuel, a time earlier. can i quantify those fuel consumptiopn figures, no, i can't. Hows about this way. on those same hills on US19, that i have previously described, there is a small hill in between two of the largest. if i go down that hill, in gear, at a starting speed of 55mph, i have to use about 40% throttle half way up that minor hill in between, in order to stay above 45mph. If I coast down the first hill, in neutral, at a starting speed of 55mph, i am up and over the small hill, and 20% or so up the next big hlil before my speed drops to 45mph.Which uses more fuel? 90 seconds at idle, or 30 seconds at 40% throttle. >>>>Modern brakes are designed to cope with small aplication loads for >>>>longer periods of time. Many car manufacturers do these kinds of [quoted text clipped - 14 lines] > >rubbish. of cours,e you say its rubbish, so it must be so. no proof, no research, one single word. modern brakes are not as simple nowadays as the brake systems of the 60s and earlier. you do know what 'direct corrolation' means, don't you? it means there is a very simple, linearr (no quadratics, or logarythmic functions) equation, of the form y = kx where k is some constant. charting retardation ability against temperature. >> no straight >> line graph that starts with retardation ability being at max when the [quoted text clipped - 5 lines] >temperature rises, and they do, you want the initial temperature to me >minimized. yes, i notice your phrasing, "*IF* the brakes fade more as the temperature rises" they do, but its not a straight line graph. You don't have maximum retardation at 20C, and complete failure at say 300c, and at 150C they're only at 50% strength. >> There is instead a gradual decrease from the >> brak systems optimal temperature (whichis NOT air ambient) to the 'max [quoted text clipped - 3 lines] >physical way brake temperature can decrease if you're dumping kinetic >energy into them. Lets use the tank analagy. Its one often used to illustrate energy changes. You have a water tank, and you have a tap, or hose, that puts water into that tank. the water is the amount of thermal energy. if the tank has a number of perforatiosn in it, to allow the water to leave the tank, is there any way the hose can be running, and yet the level in the tank decrease? yes, simply, the amount of water leaving the tank via the holes, can be greater than the amount brought in by the hose. its a fitting analagy, since the greater the water level, the higher the pressure, and the faster the water leaves, same as the radiative and conductive levels of a body to its surroundings increases as the thermal difference between the two increases - a fact easily verifyable with a cup of boiling water, a thermometer, and a watch - just measure the temperature every minute. >>>>You're also on the assumption tha when coasting, people ride the brake >>>>instead. you know, i've never done that. if i coast, i don't then ride [quoted text clipped - 11 lines] >down grade upon any highway shall not coast with the gears of such >vehicle in neutral." great, thats california, and they have, from experiance, some of the stupidest, and most politically minded laws there. For isntance, i had an event out in Long Beach in 99 - mainly gasolene and electricaly powered vehicles, and the possibility of ONE alcohol powered one. Because of that possibility, HALF our fire extinguishers had to be water, and not CO2, because that was state regs. The additive requirement has already been argued elsewhere on this group in the last day or two, now they're thinking about (last i heard) certifying hybrids like the pruis as suitable for carpooling, even with single occupancy, on the highways. I've already stated elsewhere how modern diesel vehicles (available in europe, but not the US) get much better consumption figures than any hybrid can, or does, and yet despite this easily available, vastly documented fact, the laws are still considered. One states regulatiosn banning a practice does not hold for all states. No moreso than, say, west virginia's ban on radar detectors doesn't make them illegal in the rest of the country. >>>>As for the 'not in full control' argument, again, thats from the 50's >>>>and 60's before the advent of the nice modern synchromesh. [quoted text clipped - 13 lines] >you're not competent or the vehicle is defective and shouldn't be on the >road. again, synchro is irrelevant. irrelevent, you've just proved my point. without it, youll have to double-clutch, taking time, and some thought, meaning att he critical time, you're not placing full concentration on avoidance, as you're attempting to match engine RPMs. nor can you, as you have called a requirement and the whole reason its so illegal, slap it into the lowest gear possible and let the clutch take a heavier load, dumping it to rob the vehicle of more speed as the energy is transfered to rotating the engine fast enough to match the wheel speed, throught he transmission. In an emergency, as you claim this whole thing is the reason for, this method slows the vehicle substantially quicker than double clutching, can, or allowing the automatic gearbox to kickdown on its own. . >>>>For an >>>>avoidance measure, engine power or no will make no difference. [quoted text clipped - 7 lines] >off the brakes!!! it also allows you to instantly re-power the vehicle >if required. what substantial laod off the brakes? I think my actual experimental figures show that at best, they'll work as quarter as well as brakes. however, they make no difference to the braked stopping distance. In fact, since the braking is so much quickre than the engine-braked time, the brakes are actually having to dissipate the inertia of the engine and flywheel AS WELL. You can't have a connected system slowing down at different speeds. the engine wants to slow you from 50mph in about 450ft. the brakes want to slow you from 50mph in 100ft. therefore the brakes must dissipate 4x the energy of the engine, and so, for each watt of energy the engine dissipates, the brakes has to dissipate 3 for the engine. >>>>For >>>>stopping, your braking speed is limitedby the static friction lmiit of [quoted text clipped - 14 lines] >no, it's necessary to keep the brakes cool for maximum stopping power. >remember the temperature delta thing??? really. then why is it, after 6 heavy braking runs, one after another (to test distance repeatedly for neutral and in gear) could i still do a 4 wheel lockup on demand. 6 times I'd dumped excessive amounts of heat, with little ventalation cooling into the brakes (6 stops from 50mph to 0mph, with the resulting lack of airflow over the brakes that comes with motion) and they hadn't faded. This was both vehicles. No standard pads, both vehicles at their standard weights, a bit over if anything, what with the car seats, vcr, tools+fluids in the van, and 200lb of batteries in the back of the civic (lots of lovely hawker SBS30's- never know when they'll come in handy). They were hot, yes, faded, no. Both vehicles had standard pads, regular ones from autozone, civic's changed in december (all 4, plus master cylinder) and the caravans in march (front only, plus master cyl). Lovely and humid here too, so when i check the fluid levels, you can be sure they get some moisture from the air. Brake lines are original, but don't appear to have any cracks. Heavy loads, lots of heat, possibly wet brake fluid, not-new pads, still NO FADE. perhaps you ought to rethink your theory somewhat. I could even probably work out for you the approximate brake temps after the first run, if you really wanted. I'm sure that would be 'hot enough' for you. >> I did some tests this adrernoon, using two automatic vehicles, using >> an old airstrip here. I weighted things in your favour, by using older [quoted text clipped - 34 lines] >to increase engine braking. i guess you'd never notice that if you >habitually coast in neutral, but it's fact nevertheless. well, lets see. i did listen to the engine. under the heavy braking, i didnt hear it shift once, not in D, or D3 in my civic. Something i will check tomorow, when its light, is which gears have engine braking on them. Its something that just poccured to me. The onyl automatic my father had, was a 1979 ford granada, 2.8 ghia. It had no engine braking on its 3rd speed. >>>>In fact, you're not having to brake the rotational >>>>inertia of the engine and connected gearbox componants, so you're [quoted text clipped - 18 lines] >so these situations never occur? you should know that it does rain >occasionally... Oh, i know rain very well, being a brit. i know if a lot better than you do in Sf. The only time you use or need piower still, is to drive a car out of a rear-wheel slide, and even then only REQUIRED if its over a certain angle, 30-45deg, depending on car balance. OR to go faster. In any other situation, excess of power will not help. dynamic friction (when a wheel is spinning in comparison to the ground, aka a skid)) is less than static (the normal driving method) and so an excess of power would not help, except to provide some form of force tangental to the slide to correct, or for acceration. I think i've said these two reasons, these ONLY two reasons enough times, in enough ways for even you to understand. >>>>Regardless, I'm sure we'll be able to go around in circles like this, >>>>each counter-claiming the other. Instead, i'll send an email over to [quoted text clipped - 15 lines] >/increased/ engine braking for downhill situations. one of these >situations does not compute. i HAD one of theem. A 1986 'rubber band' volvo 340. it wasn't so much a button that incrased engine braking, it was just one that locked the transmission ratio to a fixed number. was mainly used for towing, and hill climbing. I still ahve a 340 in fact, but a 89 manual tranmission one. Its my work vehicle when i'm in thre UK - love them. >> This, like any long term myth, is one that clearly won't go away after >> having being delt with in common sense. In short, you say that if you >> coast down any hill, you must coast down all (can't pick your >> situation, as you call it) and you must ride your brakes at al times. > >you're the guy riding brakes. i use the engine. i'm not now, nor have i ever ridden brakes. show me where i said i have. You're the only one that can't seem to understand that the only way to coast is to then ride your brakes. Who can't understand that you can instead let your vehicles momentum incrase, just as if you were using your accelerator slightly down the hill. >> Oh, and you have an old brake system, that's been poorly maintained, >> so they would fade to nothing (despite the fact it would fail at the [quoted text clipped - 12 lines] >into heat falls. let me know if you can grasp that concept, then we can >continue this discussion. Oh, i understand the concept just fine. Lets see if you can grasp the more basic one. coasting, does not require riding the brakes. if the hills incluide is such that you must ride the brakes, you don't coast. its a judgement thing, Clearly you have no judgement. Here's another thought to ponder. By your definition, push-starting a vehicle, is not only illegal, but impossible. illegal because push starting is, at its basis, coasting, and then putting the car into gear. This is clearly illegal all over the world, since theres a law about it in California. Secondly, its impossible because, whilst caoating, you have your foot on the brake, riding it. You ride your brakes when people are giving youa push, and they'll wake your a.s up in a hurry. When you can get THAT concept, that coasting does not require riding the brakes, that continuance of a limited speed is not the aim, rather the utlisation of the concervation of momentum, , then by all means post back. If you still haven't grasped that, then don't bother. <heavy snipping done before and after, to get to the cux> >>no, it's necessary to keep the brakes cool for maximum stopping power. >>remember the temperature delta thing??? [quoted text clipped - 19 lines] >approximate brake temps after the first run, if you really wanted. I'm >sure that would be 'hot enough' for you. Ok, i just spent the last half hour or so getting some figures to match to my facts. The difference in values for the figures for a fast emergency stop to zero, and for riding the brakes was even greater than i thought. and to vastly simplify the maths (so i comfortably got the entire set of calculations on s single sheet of paper, i even made many assumptions in your favour. Lets see them brakes burn!. I'm using for the vehicle, my 88 honda civic DX - partly since its relevent, this being a honda group, but also because i had the figures for it to hand, unlike the caravan, and its been so much longer since its brake service (which plays to you) Mass, approximatly 1000KG (2200lb) Its about right, and makes a nice easy figure for calculations. for the rapid braking, i'll use the 50mph distance from yesterday, but attribute itt o a speed of 55mph - eases to your argument, since its more energy dumped into the brakes, and saves me calculating too many values. For the 'coasting and riding your brakes' which i'll call 'coasting' now, I used the model of the hill on US19 that i've previously mentioend. cresting the hill at 55mph, in gear the engine braking keeps the speed at 55mph, or thereabouts, unchecked it gets to about 65mph, in the distances of about 1 mile. Thus, i'll call the difference in KE between 55mph and 65mph (now see why i picked 55mph as the speed for the braking distance above) as the amount dumped into the brakes, or engine going down a hill. Kinetic energy: (1/2 Mv^2) brake - 0.5 x 1000 x 24.5872^2 (using meters/sec) = 302,265.2 J coast - 0.5x 1000 x 29.6576^2 - 302265.2 = 422172.05 - 302265.2 = 119,906.85 J Hmm, the coast energy is only just over 1/3 the brake energy. Oh dear, not looking good for your argument... Lets see about how much energy per second is put into the brakes per second. I'm assuming, of course, that the vehicle only has front brakes. Again, simplifies for me, and is biased towards your claims. assuming a linear speed decrease - it isn''t, i know, but as its a quadratic decrease, divide it by your straight line assertation of brake performance decrease with temp,a nd it comes to a near linear line 55-0 mph in 100ft is a time of 2.47sec. 55mph to cover 1 mile is 65.44 seconds. joules per second works out as brake - 302265.2 / 2.47 = 122374.57 J/s coast - 119906.85 / 65.4 = 1832.3174 Hang on, notice something there? in one second, the emergency stop has absorbed more energy than over the entire run of the coast. Odd... Now, i mentioned temperature just before. how hot will it get? Again, for simplicity, all the energy is going into heating the brake discs only. There is NO cooling effect allowed for. This HEAVILY favours your arguments, and this is where you win through, clearly. The weight of each brake disc for a honda civic is 10lb, or 4.54Kg. The specific heat capacity of cast iron is 460J/Kg/K - or, in other words, for every 460J of energy put into it, 1Kg of cast iron will be raised 1 Kelvin (or 1 Centrigrade) in temperature. Lets dump those energies in, shall we? Remember, 2 discs, (or rotors if you will) so 9.08kg lets see then brake - (302265.2 / 9.08) / 460 = 72.36K rise. coast - (119906.85 / 9.08) / 460 = 28.70K rise. Lets say the ambient temperature here in georgia was 90F, or 32.2C. We add those figures, and what do we get? brake - 104.2C - 219F coast - 60.9C - 141F look att hat, If we used water as our brake fluid, assuming it was run right onto the disc, it would have boiled. What are the boiling points for brake fluid? acording to govt. specs, the WET boiling point of DOT3 brake fluid (3.7% h2O by vol) is 284F - significantly higher than the maximum possible temperature of any braking componant in these tests. in short, your claims and assertations are utter bullshit. I've given the amth, worked it through. Where i've had to approximate, i've done so heavily biased in your direction (front brakes only, no cooling, all temperature udmped into one comonant only) and even then they were a ways away from failure point. As I said, only very badly maintained brakes would fail the way you claim happens, and only then if you heavily ride the brakes as you coast, and if that were to happen, you'd be a lot more f.cked if you had to do any kind of emergency stop. Just as an aside, any ideas what sort of speed that coast energy figure represents? just 35mph. So, a car that has the braking from 35mph spread over a mile and still has brake failure - sounds like you've got a lot of problems there. thats the brake failure utterly annihilated, even for your claims that you have to be riding the brakes. AS for 'full control' - the only two manouvers, as i've said before now, is aceleration (which was what you were trying to counter with your engine braking anyway) and to correct rear wheel skids. anything else you do NOt want the application of power, and thus having the engine connected to the wheels is meaningless. hope i've enlightened you with how things actually, numerically work in the real world, or even in heavily biased 'jim beam world'. If you can prove any factual, or numerical problems with my figures, then go ahead, if not, why not act like a man for onec, and actual admit you were wrong. <snip> dude if i've been short tempered or even rude, i apologize. i'm really not interested in personalizing any disagreement, so in future, let's just try and stick to the tech stuff. and i'm pushed for time right now, so i'm not in a positon to do a point-by-point review of your posts, but i hope to get back to you later in the week. meanwhile, other than to say that your "filling tank" analogy is absolutely on-target and that i disagree with a lot of your other stuff, check out the following: http://encyclopedia.laborlawtalk.com/disc_brake http://www.whnet.com/4x4/brakepads.html http://www-personal.engin.umich.edu/~jbarber/animation.html http://www.e-z.net/~ts/ts/Brakfade.htm ><snip> > [quoted text clipped - 12 lines] >http://www-personal.engin.umich.edu/~jbarber/animation.html >http://www.e-z.net/~ts/ts/Brakfade.htm Whats more to say, the maths is there. Its broken down simply. Its heavily biased towards your degrees, and it STILL doesn't come close to your predictions of doom. Taken a car, made it stop from a faster speed, using front brakes only, eliminated cooling, eliminated heat dissipation, eliminated heat spread, and its still only equating a 35mph stop. you're talking sh.t. If you can disprove the maths, do so. You can't get more 'tech stuff' than simple mathematics and physics. You know, energy calculations. I'm Kinda busy at work myself too - you know, got car designs to work on, funnily enough, i start work ona braking system on thursday. The maths though i purposefully kept simple, just so you could follow it - took me less than half an hour, start to finish, and that included getting references. Any website you care to try and use, as a reference will actually detract from your argument. theyll point out heat dissipation, ablation energy disipation, thermal transference, ventilation and all those other things which DROP the temperature of the brakes from the peak temp. None of this matters though, as you still claim that riding your brakes as a check speed causes excessive heat buildup and failure. As i more than amply demonstrated, all things being equal, the braking energy required to keep a vehicle at a speed when it would normally go faster is insignificant in reference to any form of sudden stop. in short you say that putting 1832J of energy into a braking ssytem per second leads to failure - equivilent to a stop of 2mph. You'd best get back to work though, must be time for you to change all the oil at the McD's you work at. You sure as hell don't work in any technologically related field. ><snip> > [quoted text clipped - 7 lines] >that your "filling tank" analogy is absolutely on-target and that i >disagree with a lot of your other stuff, check out the following: Oh, i checked out your links too >http://encyclopedia.laborlawtalk.com/disc_brake Factually incorrect in many areas. A good example was the MMC piece, which is WAY off the mark. The MMc brakes didn't require a high temperatureand ran cooler, due to the differing method of ablation used. The manufacturer is still very much in operator (and theres not just one, there's many) the reason for the change was for reasons of cost. The first few thousand were done 'cheap' but after the initally licensed 2000 sets, the full costs were passed onto lotus. Hence after chassis number 3700-ish, they switched perminantly back to cast iron discs. Oh yeah, there was also some question of wet operational ability. http://www.elises.co.uk/components/s1/brakes/ is a better link on that detail, for instance. >http://www.whnet.com/4x4/brakepads.html A sales page about a new 'type of brakepad' - basically one that has an integrated anti-squeal shim, whoopie. >http://www-personal.engin.umich.edu/~jbarber/animation.html This is the only one of any relevence. It does show a disc getting to the point of DOt3 wet boil after appoximatly 36 seconds. i have sent an email to Prof barber (and as a fellow brit, he'll help me out (especially as i believe i have a friend who was studying mechanical engineering at cambridge at the same time as him) and i'm sure we'll find that he was putting excessive braking loads throguh a single disc. I wouldn't be surprised if he was simulating at least twice the load that i calculated. I'm sure he'll drop an email back to me in the next day or so. >http://www.e-z.net/~ts/ts/Brakfade.htm Drum brakes, utterly irrelevent. Thermal masses and mass ratios, plus heat dissipation figures are massivly different to those of disc brakes. Also, unless i'm very much mistaken, drum brakes haven't provided more than about 40% of braking ability in any vehicle made in the last 30 years. in short, what little research you have done has turned up one usefull page, which is basically a thermal buildup animation, with no accompanying data. Thus whilst it is contributory, and shows how the heat builds up, it doesn't explain under what conditions this buildup of heat over time occurs. Persoanlly, i'm betting its a static jig, as in no ventilation. Again, we'll wait and see. <snip> > Ok, i just spent the last half hour or so getting some figures to > match to my facts. "getting"? you didn't do them yourself? > The difference in values for the figures for a fast emergency stop to > zero, and for riding the brakes was even greater than i thought. and [quoted text clipped - 24 lines] > brake - 0.5 x 1000 x 24.5872^2 (using meters/sec) > = 302,265.2 J first, for this to be a safe vehicle, you have to assume max gross vehicle weight [mgvw]. that's ~3000lbs or 1363kg. the brakes are no good if they can't stop the vehicle when fully loaded. that's KE = 0.5 x 1363 x 24.5872^2 i.e. 412,180J from your 55mph velocity. > coast - 0.5x 1000 x 29.6576^2 - 302265.2 > = 422172.05 - 302265.2 > = 119,906.85 J to clarify & grossly simplify, "coast" is the _additional_ energy that needs to be dissipated by the brakes if it's not being dissipated by engine braking. using mgvw, KE = (0.5 x 1363 x 29.6576^2) - 412,180 i.e. 599,429 - 412,180 = 187,249J is dissipated by engine braking. > Hmm, the coast energy is only just over 1/3 the brake energy. Oh dear, > not looking good for your argument... not sure you understand the concept, but let's continue... > Lets see about how much energy per second is put into the brakes per > second. I'm assuming, of course, that the vehicle only has front [quoted text clipped - 9 lines] > joules per second works out as > brake - 302265.2 / 2.47 = 122374.57 J/s ok, let's just get back to mgvw, so we have: 412,180J / 2.47 = 166,874W > coast - 119906.85 / 65.4 = 1832.3174 > > Hang on, notice something there? in one second, the emergency stop has > absorbed more energy than over the entire run of the coast. Odd... this is way off. the "coast" is the energy difference. you're not trying to calculate the energy dissipated by just drifting along, you're trying to calculate how much difference engine braking makes to brake temperature. per the above, if the engine is not braking the car, you need to dissipate an additional 187,249J / 2.47 = 75,809W. this is a GROSS simplification ignoring wind, friction, etc., but it'll do for first order. > Now, i mentioned temperature just before. how hot will it get? Again, > for simplicity, all the energy is going into heating the brake discs [quoted text clipped - 8 lines] > lets see then > brake - (302265.2 / 9.08) / 460 = 72.36K rise. the running surface of the disk, the bit that gets hot, is less than that because the 10lbs includes the hub part, not just the rotor. that does not heat significantly for this first order calc, but hey... so, with mgvw, that's 412,180J / (9.08lbs x 460) = 99K rise. > coast - (119906.85 / 9.08) / 460 = 28.70K rise. with mgvw, that's 187,249J / (9.08lbs x 460) = 45K rise. that gets /added/ to the rise in disk temp if you're coasting because no energy is being dissipated by the engine. > Lets say the ambient temperature here in georgia was 90F, or 32.2C. We > add those figures, and what do we get? > > brake - 104.2C - 219F > coast - 60.9C - 141F make that: 131C for normal braking, and 176C without additional engine braking but neither are anything too serious given that we're talking single application. > look att hat, If we used water as our brake fluid, assuming it was run > right onto the disc, it would have boiled. [quoted text clipped - 3 lines] > (3.7% h2O by vol) is 284F - significantly higher than the maximum > possible temperature of any braking componant in these tests. that's true, for one single stop, from cold. here's where we get to the point, and where your water tank analogy comes in: you don't just operate a brake once. for example, like my descent of filbert st, coming to a halt at each stop sign. each time you brake, you "fill the tank". particularly if you're at mgvw. now we need to figure out how quickly is the heat "leaving the tank"? in other words, to what already existing disk temp are you now adding your delta T? you want to take a shot at the heat dissipation rate? [hint: it's /less/ than the heating rate.] > in short, your claims and assertations are utter bullshit. I've given > the amth, worked it through. Where i've had to approximate, i've done [quoted text clipped - 8 lines] > 35mph spread over a mile and still has brake failure - sounds like > you've got a lot of problems there. ok, let's get to the links i posted. if you'd bothered to scroll to the bottom of this page: http://www.whnet.com/4x4/brakepads.html you'd see this: http://www.whnet.com/4x4/pix/hot_brake.jpg that looks remarkably like a disk that's exceeded 176C to me. how could that possibly be? [rhetorical]. easy, multiple brake applications that "fill the tank", just like the one i described to you for filbert st. and let's look at this: http://www.e-z.net/~ts/ts/Brakfade.htm that graphic shows brake fade. you try to assert it's "irrelevant" because it happens to mention drums, not disks. that's an extraordinarily incorrect statement considering that the friction material and the drum material in both systems is identical and their friction characteristics are temperature dependent in exactly the same way. disks don't get hot? from: http://encyclopedia.laborlawtalk.com/disc_brake we have: http://encyclopedia.laborlawtalk.com/Image:1901.jpg now, that's a stretch because it's a racing car driven to the limit, but the disks still look warm to me. [i initially included the article for the carbon disk discussion, since you raised them.] finally, from: http://www-personal.engin.umich.edu/~jbarber/animation.html we have the animated disk warming measurement where delta T is shown settling at 236C after peaking at 242C. this exceeds your worse case scenario, and still does not approach the temperatures seen in the links i've just posted. did you notice hot the temp rise starts at 98C? that's only possible if the time for heat dissipation to ambient is somewhat slower than the period to brake re-application, i.e. real world usage. > thats the brake failure utterly annihilated, even for your claims that > you have to be riding the brakes. AS for 'full control' - the only two [quoted text clipped - 9 lines] > ahead, if not, why not act like a man for onec, and actual admit you > were wrong. now, to be fair, i acknowledge that your opinion may be colored by your never having experienced brake fade, particularly if you live in flatlands that surround airfields and drive a well-braked car like a lotus elise, but to say fade does not happen is simply incorrect. let's just re-state some facts for the record: 1. fade can and does happen. 2. brake heating is exacerbated by not taking advantage of engine braking. 3. fade is partly dependent on brake materials. 4. fade is partly dependent on the rate at which a brake component can be cooled. i have personally seen brakes on a normal family sedan glow red after repeated emergency braking tests. i can personally attest to these hot brakes exhibiting significant fade. i have cited links that evidence both fade and highly elevated brake temperatures. if you've never seen, experienced or don't care to believe, hey, good luck to you. ><snip> >> >> Ok, i just spent the last half hour or so getting some figures to >> match to my facts. > >"getting"? you didn't do them yourself? Oh, naturally, i 'get them' in the sense that i ut them on a piece of paper, and work them out. >> The difference in values for the figures for a fast emergency stop to >> zero, and for riding the brakes was even greater than i thought. and [quoted text clipped - 28 lines] >vehicle weight [mgvw]. that's ~3000lbs or 1363kg. the brakes are no >good if they can't stop the vehicle when fully loaded. as long as the vehicle weights are the same for both calculations, they cancel out. using MGVW for coasting, and for braking, the 1/2MV^2 for both has the same M, and thus is equivilent. I didn't actually do the tests at mgvw either, so the braking distances, and so on are not empyrically correct. If you want to increase the value of m by 30%, you are free to do that, although it becomes experimentally incorrect, and will just raise all figures by 30%. >that's KE = 0.5 x 1363 x 24.5872^2 >i.e. 412,180J from your 55mph velocity. [quoted text clipped - 6 lines] >needs to be dissipated by the brakes if it's not being dissipated by >engine braking. Yes, exactly. At the bottom of the hill, after a coast, i would be travveling at 65mph. that is what the first of the 3 lines above calculates. The secondline removes the initial starting energy (ie that of the car at 55) o give the figure of the third line, or the energy gain through free coasting. >using mgvw, KE = (0.5 x 1363 x 29.6576^2) - 412,180 >i.e. 599,429 - 412,180 = 187,249J is dissipated by engine braking. [quoted text clipped - 3 lines] > >not sure you understand the concept, but let's continue... the 'concept' is that quite simple one. in short, cancelling out 0.5M we get 55^2 = k (65^2 - 55^2) where k is some constant. this is the raw difference in energy values. this is the crux of the argument. 3025= k (4225 - 3025) 3025 = 1200k 2.52 = k the coast energy is 2.52x SMALLER than the emergency stop energy. >> Lets see about how much energy per second is put into the brakes per >> second. I'm assuming, of course, that the vehicle only has front [quoted text clipped - 22 lines] >trying to calculate how much difference engine braking makes to brake >temperature. no, Lets reiterate what goes on, shall we? going down a hill of 1 mile length with a starting speed of 55mph. if the engine is left in gear, the vehicle stays at 55mph. if it is taken out of gear, it reaches 65mph at the bottom. Thus, the energy difference between 55mph and 65mph is dissipated by the engine over that 1 mile. In one second of braking from 55mph, the amount of energy transfered to the braking system is greater than the ENTIRE rise in energy due to coasting over 64 secondsLater on, i even calculate for you that the change in vehicluar energy due to the coast is equivilent to a stop from 35mph. thats if you want to incease the figures by 30% for 'mgvw' or not, since mass is purely a linear variable in all the calculations. >per the above, if the engine is not braking the car, you need to >dissipate an additional 187,249J / 2.47 = 75,809W. this is a GROSS >simplification ignoring wind, friction, etc., but it'll do for first order. an additional amount? wheres this come from? you seem to have just gone ahead and generated some additional energy value and added it to the emergency stop value, something to do with engine braking. Is this the added enegery value required to stop the rotational inertia of the engine in an emergency stop? >> Now, i mentioned temperature just before. how hot will it get? Again, >> for simplicity, all the energy is going into heating the brake discs [quoted text clipped - 12 lines] >that because the 10lbs includes the hub part, not just the rotor. that >does not heat significantly for this first order calc, but hey... over the 3 seconds of the emergency stop, no it wouldn't. Over the 60-seconds or so of the coast, sure it would. thats more than enough time to transfer heat. >so, with mgvw, that's 412,180J / (9.08lbs x 460) = 99K rise. > [quoted text clipped - 4 lines] >that gets /added/ to the rise in disk temp if you're coasting because no >energy is being dissipated by the engine. >> Lets say the ambient temperature here in georgia was 90F, or 32.2C. We >> add those figures, and what do we get? [quoted text clipped - 5 lines] >131C for normal braking, and >176C without additional engine braking see, this is the bit i don't get. You've taken the value for a 2.5 second emergency stop, and THEN you've added the 55mph emergency stop figure. What i'm guessing is that you're assuming someone coasts to the bottom of the hill riding their brakes, and THEN makes an emergency stop.thats something completely different, but ok. >but neither are anything too serious given that we're talking single >application. and we're talking front brakes only, AND we're discounting the huge amount of cooling flow you actually get of the brakes during that 60+ second coast, dissipating all that heat in the discs. >> look att hat, If we used water as our brake fluid, assuming it was run >> right onto the disc, it would have boiled. [quoted text clipped - 13 lines] >shot at the heat dissipation rate? [hint: it's /less/ than the heating >rate.] So, let me try and understand what you're trying to say. If you go down a steep hill, in neutral, riding your brakes, and then make an emergency stop, then accelerate up to a fair speed, and repeat, after a couple of occasions, your brakes are toast? In that convoluted situation, then yes, they would be. Is that how you drive down filbert street, or how you expect i drive down filbert street? as in [D] 35mph [N] brakes on, ride those brakes, and STOP! [D] 35mph [N] brakes on, ride those brakes, and STOP! [D] 35mph [N] brakes on, ride those brakes, and STOP! [D] 35mph [N] brakes on, ride those brakes, and STOP argh i can't stop what out people in lombard!!!!! Don't be a f.cking idiot. >> in short, your claims and assertations are utter bullshit. I've given >> the amth, worked it through. Where i've had to approximate, i've done [quoted text clipped - 19 lines] >that possibly be? [rhetorical]. easy, multiple brake applications that >"fill the tank", just like the one i described to you for filbert st. filbert street, no. Nurenburgring, silverstone, any race track application, yes. Normal road use, no. through coasting downa hill, don't be stupid. Iron gets to around that temperature at around 750C (1382F) maybe he was coasting down Everest >and let's look at this: >http://www.e-z.net/~ts/ts/Brakfade.htm [quoted text clipped - 3 lines] >material and the drum material in both systems is identical and their >friction characteristics are temperature dependent in exactly the same way. WEll, i hated to point this out before but ok... you say just before >131C for normal braking, and >176C without additional engine braking" 176c is 348F. looking at that graph, for quality linings, it seems that thats in the OPTIMUM retardation range, for a decent quality shoe. however... >On Sat, 20 Aug 2005 12:34:13 -0700, jim beam <nospam@example.net> >wrote: >you don't know what you're talking about. any brake fades as a function >of temperature. Which this graph CLEARLY disproves. It might be true for cheap low quality pads+shoes, such as the ones you buy (which you stated earlier) but *shem* i /do/ however care if [your] willful ignorance affects /my/ safety on the road. if [you] careens out of control onto /my/ side of the freeway and hits /my/ car because [you've bought cheap useless brakepads] and has lost control because his brakes are toasted, he'd better make sure he can run faster than me, because i /will/ be upset. Sorry, just had to change your statement from ealier to reflect my attitudes, and yours. You buy cardboard brakepads, and then drive like a bat out of hell down filbert, i will make you regret it. >disks don't get hot? from: >http://encyclopedia.laborlawtalk.com/disc_brake [quoted text clipped - 3 lines] >the disks still look warm to me. [i initially included the article for >the carbon disk discussion, since you raised them.] And what you didn't realise, it seems, is thats those rbakes functioning at their ideal temperature. Go watch any high end motorsport, and you'll see that. Cars at LeMans will do that all day long, and have no problems. These are not running the same braking systems as you and me on the roads www.canadiandriver.com/articles/tw/brembo.htm "Many racing brake systems use discs of carbon composite material (often misnamed "ceramic") which offer long life, light weight and exceptional braking efficiency, among various benefits. In race-car applications, these brakes can glow red-hot under hard use. So far, only a limited number of exotic sports models offer carbon discs, but I wouldn't be surprised to see their use widen over the next few years." >finally, from: >http://www-personal.engin.umich.edu/~jbarber/animation.html [quoted text clipped - 5 lines] >somewhat slower than the period to brake re-application, i.e. real world >usage. I have yet to get a reply back from the Professor, but bet you that the disc was completely stationary, and the applied brakepads were rotated agaisnt it. This makes experimental sense, since that way, the wires for the temperature sensors don't end up being all twisted, and you ahve more control over the frictional energies, plus don't require arotation rig for the disc, and a compression rig for the pads, Thus there is zero coling due to airflow, which is how modern brakes are cooled. Again, i point out that it shows vastly increased heat buildup than even your emergency stop AFTER riding the brakes can show. at 36 seconds its still a ways hotter than after 66 seconds by your worst calculation. I think the best way we could give a qualitative aspect to that is a prelude at mgvw going down filbert street, with only the front right brake from an 88 civic working. however, lets not lose sight of what that annimation tells us, and ONLY what it tells us. under an unspecified (but very large) braking force, with unspecified componants, non-uniform heat buildup occured across the face of the disc. thats ALL that says, nothing more, nothing less. No indication of the materials used, no conditions listed, Thus inferrence to everyday use is useless, and unwise, since the relevence to everyday conditions is unknown. In fact, considering he was testing the pattern of heat buildup, i wouldn't be surprised if he took all possible efforts to reduce as far as possible the ability of the disc to cool. >> thats the brake failure utterly annihilated, even for your claims that >> you have to be riding the brakes. AS for 'full control' - the only two [quoted text clipped - 14 lines] >flatlands that surround airfields and drive a well-braked car like a >lotus elise, but to say fade does not happen is simply incorrect. First time i've ever heard of northern/central georgia as flatland. Nor are 88 civic, or 87 caravan (the two vehicles i did the brake,a nd engine-braked stops with) elises. In fact, an elise would have favoured you, since that cars engine is so much bigger in relation to the vehicles overall weight, on the same hill that engine braking keeps me at 55 in my two US vehicles, it would actually slow me down in the elise. Of course, i don't have an elise, and my friend with one is back in the UK. I am hankering after an atom2 myself (which, in case you don't know, is the 3rd fastest street legal vehicle around a track, as tested by top gear, beaten only by the Ferrari F60, and the F60 based Masserarti MC12, from a supercharged JDM civic type-R engine,) Tell you what though, if you think Filbert street is bad, go south a little to Portola vally, and try Old Spanish Trail. If your brakes cooked in SF, you'll not make it a quarter-way down that. my friends who live there (and with whom i sometimes stay when i work in SF) would surely crash into a ditch, if they drove in the apprantly reckless and careless way you do. just part of the road (vista verde, from old spanish trail, or ramona road) is a 1 in 6.8 gradient (worse than filbert, and its not even half way down). overall its 4.2 miles from the interstate, averaging 1 in 19 >let's just re-state some facts for the record: > >1. fade can and does happen. Can happen yes. Does happen, no. not in all but extreme circumstances, or on badly maintained vehicles. >2. brake heating is exacerbated by not taking advantage of engine braking. If the 1800W (the amount engine braking dissipates) in the real-life coast example, would make such a big difference to your vehicles braking system, you really need to get it into a shop, and have it overhauled by professionals. 122KW to stop from 55mph, averaged, and engine braking is 1.8KW. Its almost 1%. >3. fade is partly dependent on brake materials. > >4. fade is partly dependent on the rate at which a brake component can >be cooled. Persoanlly, i'd ahve lumped these together - 'fade is dependant mainly on temeprature, energy dissipation, and the frictional materials used.' >i have personally seen brakes on a normal family sedan glow red after >repeated emergency braking tests. i can personally attest to these hot >brakes exhibiting significant fade. My word, you must ahve a long neck, in order to see the brakes glow red, AND feel them fade. You ahve just disproved, though, the whole argument above, and in all other posts. REgular car brakes that glow red hot have significant fade. Not 'gotten so hot they faiiled, which is your entire argument about riding the brakes, but 'significant fade'. Any ideas how hot said brakes were? I'll give you a hint - Cast iron glows red at about 750-800C (as any machinists handbook will tell you). That is SO far above the experimental values we have both calculated above, its not funy, and still, they only had 'significant fade' They didn't fail, as you claimed coasting would do. Lets see, using our 'test' vehicle of a civic with only 2 front brakes, no dissipation to air, 1000K (you might do your brake tests with a couple of porkers next to you, but i don't) and we're raising 9.08KG of cast iron from 32C to 750C, lets round off again, and call it 720C (or Kelvin), and if you think that sort of temperature only builds up on the surface, you're dreaming - the expansion would shatter the disc. 420j/kg/k for iron.. |
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