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Car Forum / Volkswagen / Water Cooled Volkswagen Cars / October 2006Low pressure tires
Awhile back, established at this newsgroup that AC compressor use does affect gas mileage in small vehicles like an older VW with small engine. How drastically can tire pressure affect gas mileage in similar older VW with small engine (1.8L)? An example. Recommended tire pressures by VW. These are part ot the suspension system, and provide comfort for the driver and passenger. No where near the max 32 psi of same tire. What if you max hot pressure to 32 psi? What if you're running around with 15 psi for instance instead? Reason I mention is for 2 reasons. One tire (LH front) has a very slow leak. Have to refill every 2 months. I've gotten used to this, rather than having it fixed. The other reason is the two tires on the RH side decided they were going to go low, almost flat. Don't know how long they were like that. I did notice greater difficulty uphill, faster deacceleration letting off the gas pedal, and sloppy/wishwashy rearend movement at any highway steering movement. Upon refilling the RH side tires, and roadtesting, noticed opposite. Easier to climb hills, slower deacceleration, and tighter rear end movement. Am guessing the low pressure contributed to sidewall movement of the tires in turns. Pressure gauge starts showing around 20 psi. The RH tires could not move that gauge when low. Am considering 32 psi all 4 tires.  SignatureJonny A few things. You read 32 psi max on the TIRE. That applies to the tire manufacturer. They have no idea where the tire is going to be used, you could be using it on a skidoo trailer, or hauling a trailer with a cord of wet wood. It has nothing to do with a car. VW says, after doing their road tests with the car, whatever tire you put on put this amount of air in for max.tire life, comfort and good handling. That is, the psi is according to what the CAR weighs front and rear. Now, from experience, if you are running too low an air pressure, you are most likely gonnna experience a sidewall blowout, as the sidewall will be flexing more than it usually does which builds up heat and causes the failure to happen. So, keep that pressure up. As a maximum, heck my spare has 50 in it. But, if decide to run your air pressure at the high end (whether that be 35-40 odd), it will give you better fuel economy, but, you do lose traction as the tire will be wearing out prematurely in the centre of the tread....also you will feel like you are riding on the steel rims themselves when you hit bumps. You will have more get up and go with the higher tire pressure, which shows you that if you got a flat, you need more power to turn that wheel over as it is not so round as it once was. Do yourself a favour and get the tires fixed(you probably have a bead leak, which means they have to dismount the tires, clean the rims and remount again. And they (the tire shop)will stuff 32 in(or more) right away so that the bead seats itself to the rim, you can readjust the pressure later(a couple of days of driving on them) The 32 psi has been used on large Chevs and Fords for the longest time, so it is a number stuck in the shops head. If you check in the newer chevs, ford, bmw's, toyota's, they all have different numbers for the tire pressure(even though the tires(most brands) say 32 max). WW Me personally, I find that high tire pressure beats the cars suspension to death and starts the cars creaking and groaning after a year or two. If I go cross country , or have a load I go 32, Everything else #30 rides real nice and doesn't eat tires up. >A few things. You read 32 psi max on the TIRE. That applies to the tire > manufacturer. They have no idea where the tire is going to be used, you [quoted text clipped - 28 lines] > the tire pressure(even though the tires(most brands) say 32 max). > WW >A few things. You read 32 psi max on the TIRE. That applies to the tire > manufacturer. They have no idea where the tire is going to be used, you [quoted text clipped - 28 lines] > the tire pressure(even though the tires(most brands) say 32 max). > WW The last set of GYs were mounted at the GY dealer. They put in the designated pressures for front and rear per the VW recommendation for my particular vehicle model and year and body style (IE wagon). SignatureJonny Why not just replace the tires or fix the leaks? Then there's no need to worry! > Awhile back, established at this newsgroup that AC compressor use does > affect gas mileage in small vehicles like an older VW with small engine. [quoted text clipped - 18 lines] > gauge starts showing around 20 psi. The RH tires could not move that > gauge when low. Am considering 32 psi all 4 tires. A tire with incorrect pressure will wear out much faster, but worse than that incorrect pressure can lead to loss of control. That's the problem. What is the correct pressure? VW recommended by the owners manual, or repair manual for instance, or 32 psi, or what. I juiced it up to 32 psi anyway today. It rained all day. Noticed no problems in handling. The only time, as usual, is when I hit a large puddle. Causing the vehicle to swerve slightly towards the puddle during rural highway driving conditions. SignatureJonny >A tire with incorrect pressure will wear out much faster, but worse than >that incorrect pressure can lead to loss of control. > That's the problem. What is the correct pressure? Your Owners Manual should have that information, as well as the manufacturer of your tires. You can also get the info from the service department of your local dealer, which would be even a better source because they will consider the car/tire combination. As noted, the pressure on the tyre is the max for that tyre not the recommended pressure for the tyre on your car or any other car. You look at that just to make sure it is equal to or greater than the pressure you intend to use. Don't use it to determine what pressure to use. The manufacturer has recommended a specific pressure for the original equipment size tyres and had done so based on a number of controlled test tract test. Going much over or worse yet under the recommended value can cause unsafe handling. SignatureJoseph E. Meehan 26 + 6 = 1 It's Irish Math > Awhile back, established at this newsgroup that AC compressor use does > affect gas mileage in small vehicles like an older VW with small engine. [quoted text clipped - 18 lines] > gauge starts showing around 20 psi. The RH tires could not move that > gauge when low. Am considering 32 psi all 4 tires. The recommended pressures for forward and aft tires puts the vehicle at borderline danger from sidewall swaying problems with just one passenger and no load on my particular vehicle. Adding passengers exacerbates the problem, making it apparent. SignatureJonny > As noted, the pressure on the tyre is the max for that tyre not the > recommended pressure for the tyre on your car or any other car. You look [quoted text clipped - 28 lines] >> Pressure gauge starts showing around 20 psi. The RH tires could not move >> that gauge when low. Am considering 32 psi all 4 tires. Where does that statement come from? I do not recall seeing you post what the recommended tire pressure is from the sticker on your car. You have not stated what VW you have or what size tires you have. Some VWs recommend 17 psi up front and 26 in the rear. Are you using that pressure? That would make a Rabbit handle poorly but works ok for a 1967 Beetle. I have driven VWs since 1977. The only tire pressure I found dangerous was the recommended pressure on a 1966 Squareback. If you are only checking your pressure once every two months and you know you have leaks that suggests some sort of odd maintenance schedule. If your tire guage starts at 20 psi then it is the wrong guage for a passenger tire. >The recommended pressures for forward and aft tires puts the vehicle at >borderline danger from sidewall swaying problems with just one passenger and [quoted text clipped - 32 lines] >>> Pressure gauge starts showing around 20 psi. The RH tires could not move >>> that gauge when low. Am considering 32 psi all 4 tires. > Awhile back, established at this newsgroup that AC compressor use does > affect gas mileage in small vehicles like an older VW with small engine. Affects gas mileage in all vehicles, regardless of vehicle or engine size. > How drastically can tire pressure affect gas mileage in similar older VW > with small engine (1.8L)? A couple of percent. > Reason I mention is for 2 reasons. One tire (LH front) has a very slow > leak. Have to refill every 2 months. I've gotten used to this, rather than > having it fixed. The other reason is the two tires on the RH side decided > they were going to go low, almost flat. Quit screwing around, and get your tires fixed! Why put up with the problem? Don't know how long they were like > that. I did notice greater difficulty uphill, faster deacceleration letting > off the gas pedal, and sloppy/wishwashy rearend movement at any highway > steering movement. You demonstrated to yourself how much low tires will affect fuel mileage. If your handling was getting loose from low tire pressure, you're lucky you didn't have an accident. Get the tires fixed! Upon refilling the RH side tires, and roadtesting, > noticed opposite. Easier to climb hills, slower deacceleration, and tighter > rear end movement. Am guessing the low pressure contributed to sidewall > movement of the tires in turns. Pressure gauge starts showing around 20 > psi. The RH tires could not move that gauge when low. Am considering 32 > psi all 4 tires. You could try what a lot of racers do: Make chalk marks across the tread and extending a little way up the sidewall. Drive around the block, then look and see where the chalk mark is rubbed off in relation to the edge of the tread. If the chalk ends right at the edge of the tread, you're at the right inflation level. Drastic over or underinflation will show up as wear past the edge of the tread, or even an unworn stripe in the middle of the tread. Do it a few times with the pressure intentionally high and low, to see the effect on your particular tires. >> Awhile back, established at this newsgroup that AC compressor use does >> affect gas mileage in small vehicles like an older VW with small engine. > > Affects gas mileage in all vehicles, regardless of vehicle or engine size. Ever see the Mythbusters TV program? They used 2 identical Ford SUVs. One using AC, one not. No difference in mileage they said. "Myth" busted they said. I still don't believe their results. >> How drastically can tire pressure affect gas mileage in similar older VW >> with small engine (1.8L)? > > A couple of percent. Kinda depends on the vehicle and the power to weight ratio in my opinion. >> Reason I mention is for 2 reasons. One tire (LH front) has a very slow >> leak. Have to refill every 2 months. I've gotten used to this, rather [quoted text clipped - 12 lines] > If your handling was getting loose from low tire pressure, you're lucky > you didn't have an accident. Get the tires fixed! The LH front tire was up to snuff at the time. Not sure if loss of air on the RH side tires was due to mischief, or some leak. > Upon refilling the RH side tires, and roadtesting, >> noticed opposite. Easier to climb hills, slower deacceleration, and [quoted text clipped - 11 lines] > the tread. Do it a few times with the pressure intentionally high and > low, to see the effect on your particular tires. That's what I like, some "common sense" approach. I'll probably try it. SignatureJonny >> Affects gas mileage in all vehicles, regardless of vehicle or engine size. > > Ever see the Mythbusters TV program? They used 2 identical Ford SUVs. One > using AC, one not. No difference in mileage they said. "Myth" busted they > said. I still don't believe their results. Yeah, I saw it last night, in fact. Couple of doofuses with no scientific backgrounds. If they found no difference in mileage, then their measuring methods were inaccurate. You can't create energy for free, if the AC uses power, it decreases gas mileage. And AC does use power. They can't bust the "myth" of cold, hard physical reality. >>> How drastically can tire pressure affect gas mileage in similar older VW >>> with small engine (1.8L)? >> A couple of percent. > > Kinda depends on the vehicle and the power to weight ratio in my opinion. That's why it's expressed in a percentage, and not an absolute number. Besides, you specified an older VW with a 1.8 engine, didn't you? >>> Affects gas mileage in all vehicles, regardless of vehicle or engine size. >> [quoted text clipped - 16 lines] >That's why it's expressed in a percentage, and not an absolute number. >Besides, you specified an older VW with a 1.8 engine, didn't you? This whole conversation has been sort of vague. Tire pressure tag is on the door pillar or gas fill lid on the last 3 water cooled VWs I owned. I guess it was in the owners manual for the air cooled VWs but I cannot recall. I do not have any air cooled VWs to look at either. 1.8L engine. Well some folks could have a 1.8L in a 1952 VW if they did some hot rodding. Older is not a very definitive term. Kind of like a tank of fuel. My car manual says it holds 14.5 gallons US but I often pump 16 gallons in. Capacity should not be vague. It sure was not in the mid sixties VW fuel tanks. >>> Affects gas mileage in all vehicles, regardless of vehicle or engine size. >> [quoted text clipped - 7 lines] >free, if the AC uses power, it decreases gas mileage. And AC does use >power. They can't bust the "myth" of cold, hard physical reality. Mythbusters used just about the worst possible circumstances to test that particular hypothesis. They used Full-size SUVs with big V8 engines, and they did the test at IIRC 45mph because of the sharp corners on the test track they used. Silly really. The idea was to see if driving with the windows open used more gas than running the A/C. On a big SUV at 45 mph, it was a wash. On a properly aerodynamic car at a realistic highway speed, it would not be. Modern A/C compressors are extremely efficient, while driving with the windows open at 75 mph royally screws up the aerodynamics. And of course, as speed increases, the relative percentage of the engines power needed to run the A/C compressor decreases. Takes the same amount of power to run the compressor at idle as it does at highways speed. Kevin Rhodes Westbrook, Maine >>>> Affects gas mileage in all vehicles, regardless of vehicle or engine size. >>> [quoted text clipped - 22 lines] >Kevin Rhodes >Westbrook, Maine My 2003 Jetta diesel gets about 3-5 miles per gallon better mileage in the spring and fall then it does in the summer. I have windows open but not wide open in the spring and fall. AC in the heat of summer. No myth busting there. I don't worry as much about crummy mileage in the summer but if it is crummy in the fall and spring I am lookng for reasons. My 84 GTI used to lose about 10% when running the AC. About the same as the mileage loss on the Jetta as it could dip down to 45 mpg. > My 2003 Jetta diesel gets about 3-5 miles per gallon better mileage in > the spring and fall then it does in the summer. I have windows open > but not wide open in the spring and fall. AC in the heat of summer. No > myth busting there. Could seasonal fuel variations have anything to do with it? -- Mike Smith >> My 2003 Jetta diesel gets about 3-5 miles per gallon better mileage in >> the spring and fall then it does in the summer. I have windows open >> but not wide open in the spring and fall. AC in the heat of summer. No >> myth busting there. > >Could seasonal fuel variations have anything to do with it? No. Drive a week with the AC on and mileage goes down about 10%. Next tank it will go back up with no AC. I could flip back and forth as the weather does. Fuel mix does not flip but the temps do. We had a few days of frost already and then 70+ days a few days later. I do not know for sure how much the summer/winter diesel mix affects mileage. I do know straight B100 chicken fat base causes about a 5% or more drop in mileage but better smelling exhaust. I have not run soy bio in a long time. I do not know how it affects mileage. http://www.theoildrum.com/story/2006/9/13/234043/431 Their testing procedures went accurate enough. They lack relevant. information They only have an hour show. Cant drive the vehicles long enough or on identical test stands either for accurate tests. Didn't remove human error either. They did one one time about pressurized toilets in airplanes and said they wouldn't depressurize in an aircraft. They lacked information, and didn't do the right test. They are however quite entertaining. Just goes to show you infantile adults with ADD could have cool jobs too. >>>>> Affects gas mileage in all vehicles, regardless of vehicle or engine >>>>> size. [quoted text clipped - 41 lines] > the same as the mileage loss on the Jetta as it could dip down to 45 > mpg. > The idea was to see if driving with the windows open used > more gas than running the A/C. Oh, THAT myth! Okay. There's no doubt in my mind that running the AC uses much more fuel than any losses due to aerodynamics with the windows open. No way that windows could possibly cause that much drag. That is the conclusion that Road & Track reached in a recent test, too. As someone else mentioned here in this thread, there's a clear-cut correlation between using AC and loss of fuel mileage, but no correlation between having the windows open and losing mileage. Does anyone feel the car slow down or hear the engine start to pull a little harder when they lower the windows? Of course not. But you do feel that momentary bump when the AC compressor kicks in. That one really is a myth. AC costs fuel, pure and simple. Actuarially it appears to depend on the car, including the engine and transmission used as well as the speed. To tell you the truth, I don't worry about it. I keep the windows closed (almost all the time) and use heat or air as needed. I like being comfortable and the worse mileage I have ever had with my TDI is mid 40's so I guess I can afford it. SignatureJoseph E. Meehan >> The idea was to see if driving with the windows open used more gas than >> running the A/C. [quoted text clipped - 11 lines] > > That one really is a myth. AC costs fuel, pure and simple. It sounds a lot like you have alloy wheels and the wheels are leaking. Why people want those things that cost more and function less is beyond me. SignatureJoseph E. Meehan 26 + 6 = 1 It's Irish Math > Awhile back, established at this newsgroup that AC compressor use does > affect gas mileage in small vehicles like an older VW with small engine. [quoted text clipped - 18 lines] > gauge starts showing around 20 psi. The RH tires could not move that > gauge when low. Am considering 32 psi all 4 tires. > It sounds a lot like you have alloy wheels and the wheels are leaking. >Why people want those things that cost more and function less is beyond me. Did I miss something? I have not experienced tire pressure loss any faster on my cars with alloy wheels than I have on my lawn mower, tractor or truck with steel wheels. Alloy wheels leak always. Especially if it snows and the city puts rocksalt down. Across all brands. I could call 5 guys right now with leaking alloys. they leak at the bead by the balance weights from corrosion. >> It sounds a lot like you have alloy wheels and the wheels are leaking. >>Why people want those things that cost more and function less is beyond [quoted text clipped - 3 lines] > faster on my cars with alloy wheels than I have on my lawn mower, > tractor or truck with steel wheels. >> It sounds a lot like you have alloy wheels and the wheels are leaking. >>Why people want those things that cost more and function less is beyond [quoted text clipped - 3 lines] > faster on my cars with alloy wheels than I have on my lawn mower, > tractor or truck with steel wheels. No, you either have been luck or you have the very expensive high quality wheels. Not all of them leak, be there are a lot of leaks reported and they tend to be less robust than steel wheels so they don't survive pot holes very well. >>> It sounds a lot like you have alloy wheels and the wheels are leaking. >>>Why people want those things that cost more and function less is beyond [quoted text clipped - 10 lines] >to be less robust than steel wheels so they don't survive pot holes very >well. Well there you go. I moved to Atlanta half a lifetime ago. I never had aluminum or mag wheels when I lived in Cleveland, Ohio. Pot holes are sort of rare compared with the stuff I saw as a kid driving in Ohio. We rarely see road salt so clip on wheel weights do not do that much damage to aluminum wheels. The 2003 Jetta factory wheels use tape on wheel weights anyway. My 84 GTI was stripped when I got it. I took my snowflake GTI wheels off my 80 Rabbit and used them. Rabbit had a tragic incident with a telephone pole. Pole won. The snowflake wheels were made in some South American plant. I do not think they were all that high quality. I always had a bt of a shimmy or shake on two different cars and at least 4 sets of tires. The Jetta wheels are smooth as can be with quality Michelin tires not needing a balance between tire purchases of 80,000 miles. Both sets of wheels had a plastic like top coat finish which I am sure is there both to protect the exterior and to seal the interiour to reduce leaks. So far it has worked ok. I am used to checking tire pressure every week or more with bicycle tires so losing a psi or 2 once a month on the car seems like nothing. I don't think the Jetta loses air that fast. I guess I should make note of the pressure checking temp and date to see what the real loss is. Good guess, no cookie. Factory steel wheels. No wrecks or accidents. SignatureJonny > It sounds a lot like you have alloy wheels and the wheels are leaking. > Why people want those things that cost more and function less is beyond [quoted text clipped - 22 lines] >> Pressure gauge starts showing around 20 psi. The RH tires could not move >> that gauge when low. Am considering 32 psi all 4 tires. |
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