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Car Forum / Driving, Maintenance, Tuning / Driving / September 2005Properly maintained tires improve gas milage?
I'm a total novice when it comes to cars and now that I'm living on my own after college I'm trying to make sense of car upkeep myself. Overall my 2000 Jetta seems to be running well and gets pretty decent gas milage. (I don't keep track but my gas bills are never awful) But...the other day a co-worker was talking about SUV's and how having new tires or at least tires with well maintained tire pressure can mean better gas milage. Of course given the current gas prices I was interested. I thought about asking the dealer, but wasn't sure I'd get a straight answer. Anyone else heard of this? And does it apply to small cars too or is it more related to SUV's? > I'm a total novice when it comes to cars and now that I'm living on my > own after college I'm trying to make sense of car upkeep myself. [quoted text clipped - 8 lines] > Anyone else heard of this? And does it apply to small cars too or is > it more related to SUV's? Inflate your tires as much as it is safe to. You can safely exceed the pressure recommended by the car manufacturer (by as much as 5 psi, I'd say) but make sure you're below the max pressure specified by the the tire manufacturer. > Inflate your tires as much as it is safe to. You can safely exceed > the pressure recommended by the car manufacturer (by as much as > 5 psi, I'd say) but make sure you're below the max pressure specified > by the the tire manufacturer. NOT a good idea. Over-inflated tires might increase fuel economy slightly, but not to the point where you'd notice the difference at the gas pump. Meanwhile, over-inflated tires will wear out quicker (in the middle), causing you to have to replace all four tires much sooner than would otherwise be necessary. This is especially true in any state that has mandatory yearly inspections. One of the things checked is tread depth. If you have plenty of tread on the outside but the tire is bald in the middle, it's a safety inspection failure, and MANDATORY tire replacement. But to answer the OP question . . . improperly inflated tires can dramatically decrease fuel economy. If a tire is just a few PSI too low, your gas mileage might drop 10% or more. Thus, it's possible that a tire that looks OK (by visual inspection) could be costing you money buy wasting fuel. Try to check your tires at least once a month, and inflate all four of them to the pressure recommended by the manufacturer of THE CAR. You will often find this information on a sticker inside the driver's door somewhere. If not, it will be in the car's owner's manual. Gas stations used to offer free air to their customers, but those days are pretty much over. Get yourself a good tire guage for about 5 bucks and a pump of some type. Home depot (or was it lowes?) sells a tire inflator that plugs into the cigarette lighter socket and only costs about 20 bucks. Good to keep in the trunk for emergency use, anyway. -Dave > > Inflate your tires as much as it is safe to. You can safely exceed > > the pressure recommended by the car manufacturer (by as much as [quoted text clipped - 9 lines] > you have plenty of tread on the outside but the tire is bald in the middle, > it's a safety inspection failure, and MANDATORY tire replacement. To us in the UK it seems crazy that you can evade tyre inspection in some legislatures. Excessively worn tyres are a *hazard* to both the user of the vehicle and other road users. It helps to understand about the 'wear bars' that tyres today have. > But to answer the OP question . . . improperly inflated tires can > dramatically decrease fuel economy. If a tire is just a few PSI too low, [quoted text clipped - 6 lines] > find this information on a sticker inside the driver's door somewhere. If > not, it will be in the car's owner's manual. Most definitely in the manual and I just found today as I was indeed checking my tyre pressures that there's a sticker in one of the rear pasenger door jambs in my case. > Gas stations used to offer free air to their customers, but those days are > pretty much over. UK supermarkets do well in this regard. They also normally sell the least exepensive fuel. > Get yourself a good tire guage for about 5 bucks and a > pump of some type. Home depot (or was it lowes?) sells a tire inflator that > plugs into the cigarette lighter socket and only costs about 20 bucks. Good > to keep in the trunk for emergency use, anyway. -Dave I bet you'll find a tyre inflator on ebay for less than that even. Graham > To us in the UK it seems crazy that you can evade tyre inspection in some > legislatures. [quoted text clipped - 4 lines] > > It helps to understand about the 'wear bars' that tyres today have. Yeah, I forgot to mention that. You are absolutely right. The number one reason to maintain tires and inflate them properly is so that the vehicle itself is SAFE to operate. Doing so will also make it more fuel-efficient, but safety should be the primary concern. It's been my experience that all the tires I've driven on lose most of their traction long before the tread depth gets low enough to reach the wear bars. I know the states I've lived in most recently, the tires would fail yearly inspection anyway, long before the tread depth reaches the wear bars. But, you make another good point. If your tread depth reaches the wear bars, you probably should have replaced those tires LONG AGO. :) -Dave > It's been my experience that all the tires I've driven on lose most of their > traction long before the tread depth gets low enough to reach the wear bars. Maybe in the rain. In dry conditions, tires worn down to the wear bars have *better* traction. Ask any racer. -- C.R. Krieger (BT, DT) >> It's been my experience that all the tires I've driven on lose most of >> their [quoted text clipped - 4 lines] > have *better* traction. Ask any racer. > -- Unless that tire has also aged as it wore, leaving it hard and slippery. I have seen tires, stored for too long put back into service, giving almost no grip at all. Bernard >> It's been my experience that all the tires I've driven on lose most of >> their [quoted text clipped - 3 lines] > Maybe in the rain. In dry conditions, tires worn down to the wear bars > have *better* traction. Ask any racer. This is true for new tires that have been shaved, but tires that have actually been worn down over time (many miles, many months) may not have such great traction. Ed >> It's been my experience that all the tires I've driven on lose most of their >> traction long before the tread depth gets low enough to reach the wear bars. > >Maybe in the rain. In dry conditions, tires worn down to the wear bars >have *better* traction. Ask any racer. Those guys wear the tread off quickly. By the time the tread has worn off the average tire, processes more related to time than miles mean the rubber isn't so good anymore.  SignatureThere's no such thing as a free lunch, but certain accounting practices can result in a fully-depreciated one. >>Inflate your tires as much as it is safe to. You can safely exceed >>the pressure recommended by the car manufacturer (by as much as [quoted text clipped - 3 lines] > NOT a good idea. Over-inflated tires might increase fuel economy slightly, > but not to the point where you'd notice the difference at the gas pump. It all depends on how seriously one should take the car makers recommended pressure. IMO the car manufacturer's recommended tire pressure was made with *ride comfort*, and not handling or fuel economy in mind. > >>Inflate your tires as much as it is safe to. You can safely exceed > >>the pressure recommended by the car manufacturer (by as much as [quoted text clipped - 10 lines] > made with *ride comfort*, and not handling or fuel economy > in mind. That is true. Exceeding that pressure will result in some mpg gain and will not cause excessive tire wear. Only if the tire is inflated grossly above the recommended with the 'wear in the middle' effect happen. Lots of recommendations by auto advice jounalists to do it. Harry K >>>Inflate your tires as much as it is safe to. You can safely exceed >>>the pressure recommended by the car manufacturer (by as much as [quoted text clipped - 11 lines] > made with *ride comfort*, and not handling or fuel economy > in mind. Why do you think this? I am sure ride comfort is one of the factors a manufacturer includes when determining the tire pressures, but with CAFE requirements being what they are, I believe car manufacturer's are likely to give achieving the highest possible fuel mileage a reasonably high priority (second only to safety and above ride quality). Ride comfort can be addressed with shocks and springs and isolator bushings without affecting fuel economy. I have been running a personal experiment on this courtesy of GM. I have a Saturn Vue. When delivered GM recommended 30 psi in all four tires (and this is what I ran). After the NHSTA suspension failure fiasco and the subsequent recall, they changed the air pressure recommendation to 35 psi for all four tires (and I did as recommended). I keep a gas mileage log for the car, and the change in air pressure has made no significant different in my fuel economy (and this is over many thousands of miles of driving with each of the recommendations). Nothing else was changed except for the pressure in the tires (same driver, same driving pattern, same tires, etc.). I have not seen any problem with excessive tire wear since I changed to the new pressure recommendation. However there are two negative effects - ride is worse and the handling is awful. The car is now very "nervous." and tends to react to every ridge in the road. I have lived with it for 6 months, but after I replace the tires, I may go back to the old recommendation (or maybe 32 all around). This will depend on how the car feels on the new tires. I currently have Bridgestones on the car, but will probably replace them with Michelins. All things being equal, I don't think running an extra 2 or 3 psi in the tires will hurt anything, but in most cases I don't think it will make much difference in your fuel economy either. And if you do a lot of driving on gravel roads, running a significantly higher pressure can make the tires more vulnerable to stone bruising (lots of personal experience with this problem). Ed Well, you may be right then, since yuo have run that 'experiment'. I'll try giving the recommended pressure a shot :) On the other hand, Nissan recommends significanly higher pressures if you expect to exceed 100 mph for extended periods of time, so I guess that handling is not supposed to be adversely affected at those higher pressures. > On the other hand, Nissan recommends significanly higher pressures if you > expect > to exceed 100 mph for extended periods of time, so I guess that handling > is > not supposed to be adversely affected at those higher pressures. That's odd, considering that the tire will overinflate itself when it gets hot, which is likely to happen at 100MPH or higher. -Dave >>On the other hand, Nissan recommends significanly higher pressures if you >>expect [quoted text clipped - 4 lines] > That's odd, considering that the tire will overinflate itself when it gets > hot, which is likely to happen at 100MPH or higher. -Dave The reason it gets hot is the flexing of the tire wall, which increases in frequency with speed. A tire that's more inflated to begin with will flex less, so it will end up less hot. >>>On the other hand, Nissan recommends significanly higher pressures if you >>>expect [quoted text clipped - 8 lines] > in frequency with speed. A tire that's more inflated to begin with > will flex less, so it will end up less hot. Outside of the US, most car companies still provide alternate pressure depending on vehicle load and maximum expected substained speed. I think the uS single pressure number is a result of CAFE rules. When they run the CAFE tests they adjust the pressure as specified. If the secifications allowed for a lower pressure, that is what would be used. So instead of a set of recommendations based on anticipated operating conditions, we get a one number fits all recommendation. This number is almost certainly on thehigh end of the acceptable range since it has to work for maximum loads and maximum US speeds (probably 85 - 90). Michelin does recommend increasing pressure for substained high speed driving. Here is a statement from the Harmony tire line specs: For high-speed driving, additional inflation pressure and possibly reduced tire loading and/or upsizing is required. In the absence of specific recommendations by the vehicle manufacturer, use the following guidelines based on those in the European Tyre and Rim Technical Organization Standards Manual. For speeds over 160 km/h (100 mph), load and inflation must be adjusted according to the table below. S-Speed Rated Sizes: Maximum Speed (mph) 100 106 112 Inflation Increase (psi) 0.0 1.0 2.0 Load Capacity (% of max.) 100 100 100 T-Speed Rated Sizes: Maximum Speed (mph) 100 106 112 118 Inflation Increase (psi) 0.0 1.0 2.0 3.0 Load Capacity (% of max.) 100 100 100 100 Ed >> On the other hand, Nissan recommends significanly higher pressures if you >> expect [quoted text clipped - 4 lines] >That's odd, considering that the tire will overinflate itself when it gets >hot, which is likely to happen at 100MPH or higher. -Dave Increased pressure means reduced flex, which means less heat build-up at higher speeds. SignatureThere's no such thing as a free lunch, but certain accounting practices can result in a fully-depreciated one. >Why do you think this? I am sure ride comfort is one of the factors a >manufacturer includes when determining the tire pressures, but with CAFE [quoted text clipped - 3 lines] >addressed with shocks and springs and isolator bushings without affecting >fuel economy. Probably depends on the car and tires. On one car (with the tires that came with it new), I put the pressures at the car's recommended full load pressures (measured cold). The tires still wore slightly more on the sides than the center (i.e. underinflation wear pattern, though it was not that great). Signature------------------------------------------------------------------------ Timothy J. Lee Unsolicited bulk or commercial email is not welcome. No warranty of any kind is provided with this message. > >>Inflate your tires as much as it is safe to. You can safely exceed > >>the pressure recommended by the car manufacturer (by as much as [quoted text clipped - 10 lines] > made with *ride comfort*, and not handling or fuel economy > in mind. Most car manufacturers provide a range of acceptable pressure. The tradeoffs of minimum vs maximum may not be apparent to all drivers however. >> NOT a good idea. Over-inflated tires might increase fuel economy >> slightly, but not to the point where you'd notice the difference at the [quoted text clipped - 6 lines] > made with *ride comfort*, and not handling or fuel economy > in mind. Serious question . . . you DO know what the contact patch is, don't you? Overinflating the tire reduces the size of the contact patch. That contact patch is the ONLY contact your car has with the road. You do not want to mess with it. There is no fricking way that a car manufacturer is going to try to tweak "ride comfort" by recommending an inappropriate tire inflation ressure. -Dave > There is no fricking way that a car manufacturer is going to try to tweak > "ride comfort" by recommending an inappropriate tire inflation > essure. -Dave Uhh, Dave/Ted, you *DO* know that Ford's recommendation of 26psi for the Explorer was a contributing factor in the roll-overs, don't you? Floyd >> There is no fricking way that a car manufacturer is going to try to tweak >> "ride comfort" by recommending an inappropriate tire inflation [quoted text clipped - 4 lines] > > Floyd Oh YEAH!!! I forgot about that. Maybe I should say that no RESPONSIBLE car manufacturer is going to mess around with the contact patch just to improve the ride (until the vehicle ROLLS OVER, that is) :) -Dave >>>NOT a good idea. Over-inflated tires might increase fuel economy >>>slightly, but not to the point where you'd notice the difference at the [quoted text clipped - 11 lines] > patch is the ONLY contact your car has with the road. You do not want to > mess with it. True. But another factor is the lateral flexibility of the tire (shear), which adversely affects handling, and which increases with decreasing pressure. > There is no fricking way that a car manufacturer is going to try to tweak > "ride comfort" by recommending an inappropriate tire inflation > ressure. -Dave Maybe > >> NOT a good idea. Over-inflated tires might increase fuel economy > >> slightly, but not to the point where you'd notice the difference at the [quoted text clipped - 15 lines] > "ride comfort" by recommending an inappropriate tire inflation > ressure. -Dave For decades american car manufacturers stressed low tire pressure to get that soft billowy floating sensation once called the boulevard ride. I mean really low in the range of 25 to 29 psi. Only within the past few years are they getting past it. I've owned Volvo cars for about 20 years and the recommended LOW pressure on any of them was never below 32psi. > For decades american car manufacturers stressed low tire pressure to > get that soft billowy floating sensation once called the boulevard > ride. I mean really low in the range of 25 to 29 psi. Only within the > past few years are they getting past it. I've owned Volvo cars for > about 20 years and the recommended LOW pressure on any of them was > never below 32psi. Well the proper pressure depends on the size of the tire as well as many other factors. The fact that Volvo used smaller tires for a given load than was typical US practice is one reason they had to run them at higher pressures. For instance, A 1987 Volvo 240 Sedan came with185/70TR14 Tires with a recommended inflation pressure of 36 front / 36 rear. At this pressure, the tires are rated to carry approximately 1201 lb each. The 240 weighed approximately 3000 lb. The tires can support a total load of 4804 lbs, a 1804 lb margin. A 2000 Lincoln LS came with P215/60R16 Tires with a recommended inflation pressure of 30/30 rear. At this pressure the tires are rated to carry approximately 1367 lb each. The Lincoln LS weighs approximately 3600 lb. The tires can support a total load of 5468 total, a 1868 lb margin. Now which one has the most load margin in the tires when inflated per the vehicle manufacturer's recommendations? Using under sized tires and higher inflation pressure was normal practice for European manufacturers. It saves money, but that doesn't make it right. Ed > > For decades american car manufacturers stressed low tire pressure to > > get that soft billowy floating sensation once called the boulevard [quoted text clipped - 22 lines] > Now which one has the most load margin in the tires when inflated per the > vehicle manufacturer's recommendations? I'm missing your point. The margin is about the same and it would appear the car manufacturer in both cases made the correct size choice based on that solitary statistic. We were talking about was ride and wear. And if you run that lincoln or my mother-in-law's olds at those low floaty pressures the outside of the tire will wear faster and the car will feel horribly imprecise. I can recount from personal experience that the tires fitted to the Volvo car you mentioned are not "undersized" as you imply but were entirely appropriate. > Using under sized tires and higher inflation pressure was normal practice > for European manufacturers. It saves money, but that doesn't make it right. > > Ed > We were talking about was ride and wear. And if you run that lincoln > or my mother-in-law's olds at those low floaty pressures the outside of [quoted text clipped - 3 lines] > Volvo car you mentioned are not "undersized" as you imply but were > entirely appropriate. The point I was trying to make is that you cannot just divorce the recommended pressure for a tire from the size of a tire. Volvo choose smaller sized tires for a 240 than a similar sized US car would have been equipped with. With a smaller tire, you need to specify a higher inflation pressure to achieve the same load rating as the larger tire for a given vehicle weight. Smaller tires cost less and running them at a higher pressure can improve gas mileage without causing strange wear patterns. If you ran the Lincoln tires in my example at 36 psi, there is a possibility that they would wear faster in the center. I suppose they are entirely appropriate for the car, as long as you don't over load the car. However, with larger tires, you can specify a pressure that provides at least as much load carrying ability at a lower pressure which may improve both ride and handling. Running the Lincoln tires at 30 psi is not likely to result in strange wear patterns. The combination of tires and tire pressures are appropriate in both cases. Characterizing the pressure recommendation as "floaty" is just wrong. I am old enough to remember much lower inflation pressure - 1969 Ford Country Sedan Wagon - 22 front / 27 rear. Wear on the outside edges is not only a result of low inflation pressure. My ex-wife was able to destroy almost any tires. She did most of her driving on highly cambered city streets at relatively low speeds. Ed > > For decades american car manufacturers stressed low tire pressure to > > get that soft billowy floating sensation once called the boulevard [quoted text clipped - 27 lines] > > Ed I missed the obvious...lets use cars with comparable tires...The Lincoln boat uses low profile 60 tires while the Volvo 240 uses 70 tires..... >>A 1987 Volvo 240 Sedan came with185/70TR14 Tires with a recommended >>inflation pressure of 36 front / 36 rear. At this pressure, the tires are [quoted text clipped - 5 lines] >>approximately 1367 lb each. The Lincoln LS weighs approximately 3600 lb. The >>tires can support a total load of 5468 total, a 1868 lb margin. > I missed the obvious...lets use cars with comparable tires...The > Lincoln boat uses low profile 60 tires while the Volvo 240 uses 70 > tires..... My car comes with 225/45-17 sized tires. The recommended pressure is 36 psi front and 34 psi rear (I normally run 2 psi above that). If the car is fully loaded (passengers and cargo), the recommended pressure goes up to 42 psi for all 4 tires. My winter tire size is 205/55-16. The recommended pressure for them is 38 psi for all 4. If the car is fully loaded, they recommend 42 for the front and 46 for the rear. That last recommendation makes me wonder, since that exceeds the maximum cold tire inflation pressure ... >My winter tire size is 205/55-16. The recommended pressure for them is >38 psi for all 4. If the car is fully loaded, they recommend 42 for the >front and 46 for the rear. That last recommendation makes me wonder, >since that exceeds the maximum cold tire inflation pressure ... Perhaps they are expecting you to install 205/55-16 tires that have a maximum pressure higher than 46psi? Signature------------------------------------------------------------------------ Timothy J. Lee Unsolicited bulk or commercial email is not welcome. No warranty of any kind is provided with this message. > I missed the obvious...lets use cars with comparable tires...The > Lincoln boat uses low profile 60 tires while the Volvo 240 uses 70 > tires..... The point was that the correct tire pressure depends on tire size. I specifically picked somewhat similar sized cars with radically different tires sizes and pressure recommendations in an effort to show that both vehicle had similar load margins despite the large difference in pressure recommendations. Ed > There is no fricking way that a car manufacturer is going to try to > tweak "ride comfort" by recommending an inappropriate tire inflation > pressure. Ford did exactly that, and the result was catastrophic tire failures on Explorers. >> There is no fricking way that a car manufacturer is going to try to >> tweak "ride comfort" by recommending an inappropriate tire inflation >> pressure. > > Ford did exactly that, and the result was catastrophic tire failures on > Explorers. As has been repeatedly documented, the recommended inflation pressure for Explorers was well within the ratings for the tires. Even the Firetone executives admitted this in congressional testimony. Furthermore, Ford engineers claimed that the lower inflation pressure was chosen for safety reasons (to reduce vechicle responsiveness, to sprevent rapid direction changes which could get the vehicle sideways). I owned a 1996 Explorer that came with Goodyear tires. I never once worried about the inflation presure. Similar sized SUVs from Nissan and Toyota had similar pressure recommendations to the Explorer (26 all around). The real culprit was defective Firestone tires. I do agree if they had been inflated to higher pressure, the failure rate would have been lower. However, if the tires had met the minimal industry specs, there would not have been a problem. If you want to rag on Ford for buying fourth rate tires, I am with you. However, the pressure recommendatin were not below what should have been a safe level. Ed > Serious question . . . you DO know what the contact patch is, don't you? > Overinflating the tire reduces the size of the contact patch. That contact [quoted text clipped - 4 lines] > "ride comfort" by recommending an inappropriate tire inflation > ressure. I wouldn't bet on that. Here's the tradeoff: a smaller tire contact patch makes it more likely that the car will *slide*. Sliding sideways is generally safer than getting too much traction sideways - as Ford has proven with the Roller/Ejector/Exploder's low pressures. -- C.R. Krieger (BT, DT) > I wouldn't bet on that. Here's the tradeoff: a smaller tire contact > patch makes it more likely that the car will *slide*. Sliding sideways [quoted text clipped - 3 lines] > C.R. Krieger > (BT, DT) Neat theory, but pressure too low would make for a much larger contact patch. -Dave >> I wouldn't bet on that. Here's the tradeoff: a smaller tire contact >> patch makes it more likely that the car will *slide*. Sliding sideways [quoted text clipped - 6 lines] > Neat theory, but pressure too low would make for a much larger contact > patch. -Dave Ooops, I read that wrong. I guess Ford did prove your point for ya. :) -Dave > Here's the tradeoff: a smaller tire contact patch makes it more likely > that the car will *slide*. Sliding sideways is generally safer than > getting too much traction sideways - as Ford has proven with the > Roller/Ejector/Exploder's low pressures. And much more fun :):) >> Serious question . . . you DO know what the contact patch is, don't you? >> Overinflating the tire reduces the size of the contact patch. That [quoted text clipped - 10 lines] > is generally safer than getting too much traction sideways - as Ford > has proven with the Roller/Ejector/Exploder's low pressures. Lower tire pressures will increase the size of the contact patch - not reduce it as you are trying to claim. If you pay attention to NASCAR you will notice that the tire pressures are generally on the low side and that frequently drivers have tire failures because they have lowered the pressure too much in an effort to improve handling. Higher tire pressures are not necessarily associated with improved handling. Frequently lower pressure improve grip, but it can also reduce responsiveness. And in the case of the Explorer the idea of the lower tire pressures was to reduce the responsiveness of vehicle so that it would be difficult to get the vehicle sideways in an emergency maneuver. Ed > And in the case of the Explorer the idea of the lower tire pressures > was to reduce the responsiveness of vehicle so that it would be > difficult to get the vehicle sideways in an emergency maneuver. Doesn't that increase the chances of rolling instead? I, for one, would rather be sideways than upside-down. > > I wouldn't bet on that. Here's the tradeoff: a smaller tire contact > > patch makes it more likely that the car will *slide*. Sliding sideways [quoted text clipped - 3 lines] > Lower tire pressures will increase the size of the contact patch - not > reduce it as you are trying to claim. Who claimed anything of the sort? With a lower pressure (*and* the concurrent larger contact patch), it is *more likely* that the vehicle will generate enough lateral force to roll ... and that is my point. Higher pressure/smaller contact area/less traction leads more to sliding than rolling - even if the ride sucks. ;^) > If you pay attention to NASCAR you will notice that the tire pressures are > generally on the low side and that frequently drivers have tire failures > because they have lowered the pressure too much in an effort to improve > handling. NASCAR is for morons. I work in road racing and instruct for BMW CCA (among others). I understand this stuff. You apparently misunderstood what I wrote. > Higher tire pressures are not necessarily associated with improved handling. I didn't say they were. What I said was, sliding is safer than rolling. Lots less expensive, too. Tire pressure adjustments for handling purposes is fairly straightforward as long as you know what you're doing. > Frequently lower pressure improve grip, but it can also reduce > responsiveness. > > And in the case of the Explorer the idea of the lower tire pressures was to > reduce the responsiveness of vehicle so that it would be difficult to get > the vehicle sideways in an emergency maneuver. And had the unintended consequence of making it easier to roll when they *did* get sideways. >:^( -- C.R. Krieger (Been there; broke that) Hi! > Gas stations used to offer free air to their customers, but those days are > pretty much over. Say what? They *charge* you for *air* over there? You're having me on there, aren't you? One Shell filling station I frequent (albeit not for their over-prived fuel, more for food items, newspapers etc., on the grounds that it's ideally located) has just installed a new automatic tire pressurizer. You enter the desired pressure, connect the tire valve to the tube, hit OK and watch the machine do the rest. Great. I think I'll frequent them some more in the future. (And thus, it'll pay for them to have it installed, too.) Yours, Erik. Signature"It's not a case of the glass being half-full or half-empty; more that we tipped a whole half-pint into an empty pint pot. I had to see how much was there, though, and now I know." -- Nick Hornby, "High Fidelity" > Hi! > [quoted text clipped - 4 lines] > Say what? They *charge* you for *air* over there? You're > having me on there, aren't you? Unfortunately most gas stations in my area have removed the good old large compressors with storage tanks and "free" air filing stations and replaced them with little, nosiy, and slow on demand units that you have to feed with quarters. In my area there are a couple of stations that still provide free air like in the old days. I try to frequent those as much as possible. I'll even pay them a little more for gas since I appreciate the free air. However, just so I can avoid the quarter eating air stations, I keep one of the small cheap 12V compressors in my trunk. They are noisy and slow, but they are handy too. Ed >>Hi! >> [quoted text clipped - 9 lines] > them with little, nosiy, and slow on demand units that you have to feed with > quarters. I've noticed around here many small convenience stores have those coin-op air stations installed, even if they don't sell gasoline. All it costs them is a fraction of a penny for the electricity, and they get 25-50 cents out of the customer... Signature~/Garth |"I believe that it is better to tell the truth than a lie. Almgren | I believe it is better to be free than to be a slave. ******* | And I believe it is better to know than to be ignorant." (pgp@v6stang.com for secure mail info) --H.L. Mencken (1880-1956) >> Gas stations used to offer free air to their customers, but those days >> are >> pretty much over. > > Say what? They *charge* you for *air* over there? You're > having me on there, aren't you? I wish. There are some stations that still offer free air in the U.S. Unfortunately, they are VERY FEW. And, the few who do offer free air have intentional and unintentional restrictions on it. For examples, Intentional restriction: They turn on the compressor only if you buy something and then ASK them to. It's on a timer so that it turns off after several minutes (and thus nobody else can use it unless they buy something) It doesn't matter if you spent thousands of dollars at that gas station in the past year . . . if you aren't buying something RIGHT THEN, and need air in your tire, you are out of luck. Unintentional restrictions: The compressor at the one station in town that offers free air is BROKEN for months on end. (this one could also be INTENTIONAL, I guess) Some gas stations have installed coin-operated air compressors. Typical cost seems to be: 50 cents (half of a U.S. Dollar, two "quarters") And of course, for your 2 quarters, the compressor only runs long enough to add a little air to one or two tires. Of course, why would the owner of a gas station want customers to have properly inflated tires? Under-inflated tires are good for business!!! As someone else wrote, if you live in the U.S., it's best now to own a small portable air compressor. Forget about trying to find a gas station with free air. -Dave >>> Gas stations used to offer free air to their customers, but those days >>> are pretty much over. [quoted text clipped - 4 lines] >I wish. There are some stations that still offer free air in the U.S. >Unfortunately, they are VERY FEW. Except for the million or so in California, of course... > Hi! > [quoted text clipped - 3 lines] > Say what? They *charge* you for *air* over there? You're > having me on there, aren't you? They are not charging for the air, but are charging for the cost of maintaining a piece of equipment that gets used by non-gasoline buying customers much of the time. > One Shell filling station I frequent (albeit not for their > over-prived fuel, more for food items, newspapers etc., on [quoted text clipped - 4 lines] > frequent them some more in the future. (And thus, it'll > pay for them to have it installed, too.) Be careful with automated air pumps like that. They can and do malfunction so verify the results with a good handheld gauge. In my experience they malfunction to the high side and keep filling or shutoff prematurely because of an air leak. > Yours, > Erik. [quoted text clipped - 3 lines] > I had to see how much was there, though, and now I know." > -- Nick Hornby, "High Fidelity" > > Say what? They *charge* you for *air* over there? You're > > having me on there, aren't you? > > They are not charging for the air, but are charging for the cost of > maintaining a piece of equipment that gets used by non-gasoline buying > customers much of the time. It wouldn't be that way if all gas stations offered free air, though. It's not like you're going to buy fuel somewhere and then drive SOMEWHERE ELSE to put air in the tires, if the gas station you are at is offering free air. So what are the gas station owners pissed about . . . that occasionally someone might use the compressor for two seconds to add air to a bicycle tire? If you are a gas station owner and you are not offering free air, you are basically screwing everybody . . . your customers, yourself and other gas station owners, as well. -Dave > I'm a total novice when it comes to cars and now that I'm living on my > own after college I'm trying to make sense of car upkeep myself. [quoted text clipped - 8 lines] > Anyone else heard of this? And does it apply to small cars too or is > it more related to SUV's? Of course it matters. Your tires are designed to carry a maximum amount of weight at a set pressure, thus affecting how much resistance the tire makes when rolling. When tires are on your car, they are not perfectly circular, otherwise there would be 1 point on each tire that is in contact with the ground. The tire flattens where it hits the concrete because of the weight of the vehicle, and creates a bulge before and after the areas where it makes contact. That bulge creates resistance when the tire rolls, meaning it takes more torque to roll the tire. More torque means more gas. Improperly inflated tires affect how much bulge is there. You can OVER inflate your tires as well, causing improper wear and possibly other safety issues. Just follow the manual and check your tires every couple of weeks or when the temperature drastically changes. > I'm a total novice when it comes to cars and now that I'm living on my > own after college I'm trying to make sense of car upkeep myself. [quoted text clipped - 8 lines] > Anyone else heard of this? And does it apply to small cars too or is > it more related to SUV's? Yes, as you said a well maintained tire pressure can help to improve gas milage. Check the pressure every other fillup. Increasing pressure to the maximum recommended by the car manufacturer (not the tire maker) will provide an improvement as well. Pushing the pressure beyond the car maker maximum will make the car ride like an empty lumber truck and it will not handle well at all. More importantly such bad advice will result in premature wear to the center of the tire and possible blowout. This site has all sorts of timely tips: http://www.fueleconomy.gov/ By and large, properly inflated tires make about a 3% difference in gas mileage (depends a lot on how misinflated they were to begin with). Hey, I'll take a free three percent that'll also make my car perform better and my tires last longer! * Surveys show that lots of people are driving around on one or more misinflated (usually that means underinflated) tire. The best definition of "properly" inflated for all-around roadgoing duty is probably found on the sticker the manufacturer put on the door jamb or in the owner's manual.** You really can't tell by eyeball on modern radials unless they are already pretty far off. Slap a gauge on 'em every month or every other fillup or something like that (no need to get neurotic about it unless you know that one has a slow leak) and know the truth. Cheers, --Joe * Significantly underinflated tires run hotter on the highway, and if memory serves, was widely thought to be one of the factors in the rash of blowouts with certain SUV tires a few years back. ** SUV and pickup people sometimes air them up higher (there's a max cold pressure stated on the sidewall) for carrying a heavy load, or air down for traction in soupy offroad conditions, but they too are best served for normal duty by the car maker's recommendations. Performance drivers sometimes use an old-fashioned technique called "chalking" or a new-fashioned one involving pyrometers to determine their best pressure, but not only are those advanced techniques, but they're really meant for sorting out the car for best handling, not for maximizing gas mileage. > I'm a total novice when it comes to cars and now that I'm living on my > own after college I'm trying to make sense of car upkeep myself. [quoted text clipped - 8 lines] > Anyone else heard of this? And does it apply to small cars too or is > it more related to SUV's? You'll get much better mileage and have a much more reliable car overall if you keep it properly maintained. This goes for all components of any car, including tyres. To answer your question, yes, maintaining your tyres properly will improve your mileage regardless of the type of car you drive. Cars that have a low tyre pressure typically provide a more comfortable ride, as minor bumps are absorbed better by the tyres. The disadvantage of this is worse mileage and possibly reduced tyre life amongst other things. Some have said only to use the car manufacturers recommended pressures in your tyres. Personally I disagree and like to use a higher pressure, but each to their own. If you speak to your dealer, it is pretty much certain that he'll tell you not to exceed the manufacturers maximum specified tyre pressure. I recommend you drop into your local tyre fitter, or a couple if you're keen to get a few opinions, tell them the type of car you drive, the brand and model of tyres you have, the typical sort of driving you do, and they'll be able to recommend a suitable tyre pressure for your situation. On my car, which is a large sedan, I run 38psi on the front and 34psi on the rear tyres. Remember to check your tyre pressures only when the car has been parked for a few hours and the tyres are cold. As you drive your tyres heat up, and the pressure in the tyres increase. Check your tyres in the morning, once a week or once a fortnight at a petrol station as close to your home as possible. Ideally you should also carry your own pressure gauge in your car to confirm the tyre pressure after you have pumped up the tyres. Petrol station gauges can be inaccurate seeing as customers throw them around a lot. A little basic pocket sized pressure gauge shouldn't set you back much over $5, and you could keep it in your basic tool box which I know you have in your car at all times in case of emergency :-) Make sure you have valve caps on all your tyres to prevent grit getting into the valves. Also in colder months, if you don't have valve caps and you get water on the valve, then park the car overnight, the water may freeze and force the valve open, thus flattening your tyre. This of course is easily fixed by pumping the tyre up again, but it's still a pain in the arse that's easily preventable. You should get your tyres rotated every 9000 to 12000 miles. Some say this won't gain you anything, however all car and tyre manufactures recommend it be done. If your mechanic does a good service, then he/she should remove all the wheels to properly inspect your cars brakes, so they should not charge you any extra if you ask to have your tyres rotated. There’s some more info on tyre rotation here if you're unsure of what I’m talking about: <http://www.btc.net.au/tyrecare/rotation.asp> My 2c worth :-) Hope that helps! SignatureSL "The essence of propaganda consists in winning people over to an idea so sincerely, so vitally, that in the end they succumb to it utterly and can never again escape from it" Joseph Goebbels - Nazi Minister of Propaganda, 1933 - 1945 Generally good advice but ... > Make sure you have valve caps on all your tyres to prevent grit getting > into the valves. Also in colder months, if you don't have valve caps > and you get water on the valve, then park the car overnight, the water > may freeze and force the valve open, thus flattening your tyre. Having lived my entire life where it invariably freezes our Midwestern a.ses off (say, -20 deg. F at least once every single year), I have *never* seen nor heard of such a thing. Nonetheless, a valve stem cap can sometimes hold air when a loose or dirty valve core won't. > You should get your tyres rotated every 9000 to 12000 miles. Some say > this won't gain you anything, however all car and tyre manufactures > recommend it be done. No, they don't. BMW, for one. -- C.R. Krieger BT, DT > Generally good advice but ... > [quoted text clipped - 7 lines] > *never* seen nor heard of such a thing. Nonetheless, a valve stem cap > can sometimes hold air when a loose or dirty valve core won't. I've seen a tyre drop from being well inflated to obviously quite under inflated overnight, we pumped it up again the next morning and it was fine for another many thousand km's. It wasn't idiotic kids letting tyres down as this was out on a farm in the middle of nowhere. None of the tyres on this car had valve caps on them, and it was just the one tyre that went flat. At a defensive driving course I attended a few years back the instructors also told us that ice in a valve can cause a flat tyre in cold weather. >>You should get your tyres rotated every 9000 to 12000 miles. Some say >>this won't gain you anything, however all car and tyre manufactures >>recommend it be done. > > No, they don't. BMW, for one. I forgot about BMW. In fact from memory, they actually recommend not to do it? Odd seeing as the tyre manufactures do. Regardless it boils down to personal preference really. Some don't bother, some do. I do :-) > C.R. Krieger > BT, DT SignatureSL "The essence of propaganda consists in winning people over to an idea so sincerely, so vitally, that in the end they succumb to it utterly and can never again escape from it" Joseph Goebbels - Nazi Minister of Propaganda, 1933 - 1945 > Motorhead Lawyer wrote: >>>You should get your tyres rotated every 9000 to 12000 miles. Some say [quoted text clipped - 6 lines] > do it? Odd seeing as the tyre manufactures do. Regardless it boils down > to personal preference really. Some don't bother, some do. I do :-) It's not "personal preference". It's real performance and engineering aspects. And it's not just BMWs. Every performance car with staggered wheel/tire sizes, for instance, can't be rotated. I note that the new Pontiac Grand Prix - a FWD car - has staggered wheel sizes; bigger on the front than rear. Floyd > And it's not just BMWs. Every performance car with staggered wheel/tire > sizes, for instance, can't be rotated. I note that the new Pontiac > Grand Prix - a FWD car - has staggered wheel sizes; bigger on the front than rear. Which proves that it can also be a marketing gimmick. The GP is no performance car. > I'm a total novice when it comes to cars and now that I'm living on my > own after college I'm trying to make sense of car upkeep myself. [quoted text clipped - 8 lines] > Anyone else heard of this? And does it apply to small cars too or is > it more related to SUV's? Correct tyre pressure is indeed important to mpg. Check your owner's manual. Some ppl underinflate and cost themselves money. Graham > I'm a total novice when it comes to cars and now that I'm living on my > own after college I'm trying to make sense of car upkeep myself. [quoted text clipped - 8 lines] > Anyone else heard of this? And does it apply to small cars too or is > it more related to SUV's? Keeping tires properly inflated will help the fuel mileage of an vehicle. SignatureAlan Baker Vancouver, British Columbia "If you raise the ceiling 4 feet, move the fireplace from that wall to that wall, you'll still only get the full stereophonic effect if you sit in the bottom of that cupboard." > I'm a total novice when it comes to cars and now that I'm living on my > own after college I'm trying to make sense of car upkeep myself. [quoted text clipped - 8 lines] > Anyone else heard of this? And does it apply to small cars too or is > it more related to SUV's? This is a well established fact. Check the air pressure on your car's tires once a month. This applies to all motor vehicles, but the larger the tire, the worse the hit on fuel economy will become if the tires are under inflated. >I'm a total novice when it comes to cars and now that I'm living on my >own after college I'm trying to make sense of car upkeep myself. [quoted text clipped - 8 lines] >Anyone else heard of this? And does it apply to small cars too or is >it more related to SUV's? All cars. Check your pressure regularly and adjust as necessary. ---------- Alex |
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