Tire pressure 34 psi vs 32 psi

Wheel and tire information and upgrade discussions

Tire pressure 34 psi vs 32 psi

Postby jake75 » Mon Sep 29, 2008 11:20 pm

My T&C recommends 36 psi
My former PT Cruiser was 34 psi
The Vibe says 32 psi

I know that over inflation is not recommended for tire wear and handling reasons. My question is whether a minor overinflation to 34 psi would be an issue. I have these Tire Pressure monitor valve stem caps that are 34 psi I would like to use.

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Re: Tire pressure 34 psi vs 32 psi (jake75)

Postby Whelan » Tue Sep 30, 2008 12:25 am

For me personally I always looked cross eyed at the Matrix inflation numbers. I've never had a car this low. Even when inflated properly they look like they are saggy on the bottom.
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Re: Tire pressure 34 psi vs 32 psi (jake75)

Postby Raven » Tue Sep 30, 2008 1:14 am

Not a problem, I've run as high as 47psi in 225/45/17 Nitto and Falkens.
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Re: Tire pressure 34 psi vs 32 psi (jake75)

Postby matthew7hayes » Tue Sep 30, 2008 5:45 am

I always inflate close to the maximum rating. For the tires currently on my vibe (stock as far as I know), it's 44 PSI.

I don't like them looking half-flat and I feel like I get less rolling resistance - but it could all be in my head.

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Re: Tire pressure 34 psi vs 32 psi (jake75)

Postby keithvibe » Tue Sep 30, 2008 6:35 am

your fine with that little bit of over inflation.
Just so that people know the psi is determined by the weight of the car not what the tire can hold.


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Re: Tire pressure 34 psi vs 32 psi (jake75)

Postby ColonelPanic » Tue Sep 30, 2008 9:08 am

If you were running 50 PSI I'd be concerned, but a couple pounds over isn't going to hurt a thing. I doubt you'll even notice it.

I've been running 35 PSI in the Hyundai for a while now, it calls for 30. No problems with it at all!

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Re: Tire pressure 34 psi vs 32 psi (keithvibe)

Postby jake75 » Tue Sep 30, 2008 11:54 am

Quote, originally posted by keithvibe »
you're fine with that little bit of over inflation.
Just so that people know the psi is determined by the weight of the car not what the tire can hold.

And the "weight of the car" is going to vary quite a bit depending on the passenger load and cargo.

Logically I would think the tire pressure would be less when the wheels are off the ground (i.e. on the lift) compared to when sitting on the pavement with 700 lbs (empty) of weight pressing down on each tire - like squeezing a balloon. With 900 lbs (loaded) on each wheel the pressure should increase.

The tire pressure indicator valve caps are about $9/set of 4 delivered on eBay and show yellow when the pressures goes a little under and red when more under their rating. The come in various pressure ratings 32-34-36 etc. etc. I had the 34's on my PT and kept them when I traded it in.

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Postby zionzr2 » Tue Sep 30, 2008 8:19 pm

I run at 40 psi all the way around and no problems. the ride is a tad firmer and the MPGs are a little higher.

You may not notice any between 32 and 34. It will not be a problem as long as you stay under the max pressure printed on the tire.

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Re: Tire pressure 34 psi vs 32 psi (jake75)

Postby Sublimewind » Tue Sep 30, 2008 10:26 pm

Quote, originally posted by jake75 »

And the "weight of the car" is going to vary quite a bit depending on the passenger load and cargo.

Logically I would think the tire pressure would be less when the wheels are off the ground (i.e. on the lift) compared to when sitting on the pavement with 700 lbs (empty) of weight pressing down on each tire - like squeezing a balloon. With 900 lbs (loaded) on each wheel the pressure should increase.

The tire pressure indicator valve caps are about $9/set of 4 delivered on eBay and show yellow when the pressures goes a little under and red when more under their rating. The come in various pressure ratings 32-34-36 etc. etc. I had the 34's on my PT and kept them when I traded it in.

Jake... Though it "seems" logical, it is not... check your pressure on a tire and then jack it up off the ground and check it again, zero difference..

You can actually tune the handeling of the car with tire pressures... not that it matters a lot with a Vibe, but it is possible... Pump up the rears to get more "slide" should you want that.. air up the fronts for more turn-in response... ect...

Whatever happens, the pressure stays the same barring things like the tire heating up... (32psi cold can become 36psi warm BTW)

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Re: Tire pressure 34 psi vs 32 psi (Sublimewind)

Postby Whelan » Tue Sep 30, 2008 11:15 pm

So that may be why on the AWD they have you put less in the rears. I am 35 front and 32.5 rear.
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Re: Tire pressure 34 psi vs 32 psi (Jake75)

Postby vibolista » Wed Oct 01, 2008 2:09 am

Recommended tire pressure by manufacturer tends to be a middle of the road figure for comfort and performance. Watch your tread wear, though. If you start wearing out the middle portion of the tire tread, you are probably running too much air. Conversely, if you wear the shoulder tread area more than the middle, they might be too low.
(Other things can cause weird wear patterns... misalignment, worn shocks, out of balance wheels or even a slightly bent wheel can mess things up pretty badly.)

If you put a lot of air in your tires... you get a harsher ride, but steering inputs gets a quicker response. If you keep them relatively soft, inputs get a little lazier, but the ride will be somewhat smoother. I keep my tires on the firm side for that other little benefit called stretching out the fuel numbers. In most cases, lower inflation #s yield lower mpg #s.

Never inflate more than is posted on the tire sidewall! Under inflation... below the number recommended by the car manufacturer, can be a safety issue.


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Re: Tire pressure 34 psi vs 32 psi (vibolista)

Postby NibCrom » Wed Oct 01, 2008 2:52 am

I put 32 all around. I get my best mileage that way and it's worry-free.
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Re: Tire pressure 34 psi vs 32 psi (Sublimewind)

Postby jake75 » Wed Oct 01, 2008 3:30 am

Quote, originally posted by Sublimewind »

Jake... Though it "seems" logical, it is not... check your pressure on a tire and then jack it up off the ground and check it again, zero difference..

Whatever happens, the pressure stays the same barring things like the tire heating up... (32psi cold can become 36psi warm BTW)

Well - it's logical but I guess it's not factual!

Those Tire Pressure valve caps are metal and weight about 7 grams each. I wonder if that is enough to affect the "balance".

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Re: Tire pressure 34 psi vs 32 psi (jake75)

Postby 1oldbanjo » Mon Oct 06, 2008 2:16 am

The maximum pressure listed on the side of the tire should not be used to determine how much air to use in your tires - it is the pressure rating of the tire at the maximum load the tire is rated for - and your Vibe will never have enough weight to need that much air in it. The numbers listed on the sticker mounted on your door or door pillar for the Vibe are the numbers that will provide the most tread contact and will provide even tread wear for average loading in your car. The factory has tested this car and the stock tires and detrmined what pressure the tires have to evenly distribute the load to the tread - the rear tires have less pressure because the rear doesn't weigh as much as the front where the engine and transmission are located. When you overinflate the tires you make the tire rounder and stiffer and it does roll easier - however you will wear out the tread in the middle of the tire prematurely and will not get the most miles out of your tires - and you will reduce the amount of traction that is available as the tire footprint is reduced. That flat spot on the bottom of the tire that some of you don't like is the way a tire puts a flat piece of tread down on the pavement - and making the tire rounder on the bottom will reduce the amount of traction. When you install wider tires or taller tires you may actually want to reduce the amount of pressure in the tire below what the label on the door piller calls for - as the tire is bigger and can support the weight of the car easier. For daily driving there is no reason to go above 32 pounds in your Vibe....and I bet you will get better tire life if you are down in the 28-30 psi range. If you run too low of pressure the tire will wear prematurely on the edges and you will get poor gas mileage as the tire does not roll as easy.
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Re: Tire pressure 34 psi vs 32 psi (1oldbanjo)

Postby jake75 » Mon Oct 06, 2008 6:28 am

The recommended tire pressure on the '07 T&C Van is 36 psi. I checked today when putting on the low tire pressure indicator caps I just bought on eBay and they were all at 32 psi. Cold tires - outside temp today about 70 degress. It was serviced at the dealer not long ago and I suspect that their practice is to use a one pressure fits all of 32 psi. So much (again) for trusting thet they know what they are doing. Or perhaps they really don't do all fo the routine checks they say are included with a LOF service.

Tonight when wife gets home I will check the tire pressures on the Vibe and put those 34 psi indicator caps on.

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Re: Tire pressure 34 psi vs 32 psi (jake75)

Postby BlueCrush » Mon Oct 06, 2008 6:37 am

I keep my AWD at 35psi F&R
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Re: Tire pressure 34 psi vs 32 psi (BlueCrush)

Postby keithvibe » Mon Oct 06, 2008 7:29 am

I keep my awd at 37psi atwa


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Re: Tire pressure 34 psi vs 32 psi (keithvibe)

Postby dcbridgwater » Mon Oct 06, 2008 10:35 am

Please correct me if I am wrong but I always thought that on the AWD Vibe the front tires were to be set at 35 and rear at 32 because of the extra weight of the engine over the front tires and the difference is to keep the rolling diameter of all four tires the same to reduce wear on the AWD system. So if increasing the air pressure above manufacturer spec would it be better to keep the same front to rear ratio?
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Re: Tire pressure 34 psi vs 32 psi (dcbridgwater)

Postby Whelan » Mon Oct 06, 2008 11:16 pm

As I said I keep my fronts at 35 and the rear at 32.5 as recommended on the sticker. Not sure goin to 36 would help much.
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Re: Tire pressure 34 psi vs 32 psi (Whelan)

Postby BlueCrush » Tue Oct 07, 2008 12:02 am

Quote, originally posted by Whelan »
As I said I keep my fronts at 35 and the rear at 32.5 as recommended on the sticker. Not sure goin to 36 would help much.

Don't you know that for every PSI you increase your power by 1 HP? So when I street race I pump mine up to 100psi and I always win!!! That's why I keep my portable compressor in the back at all times just in case I come upon a street race. Only problem it I always gotta tell the other guy that I need to pump up my tires so I can beat him and my compressor takes forever to get the tires to 100 psi. I'm talkin' like 1 hour per tire. So I always win, by default, since they are always too scared to wait around until I'm ready....

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Re: Tire pressure 34 psi vs 32 psi (BlueCrush)

Postby Wolfman213 » Tue Oct 07, 2008 12:22 am

Quote, originally posted by BlueCrush »

Don't you know that for every PSI you increase your power by 1 HP? So when I street race I pump mine up to 100psi and I always win!!! That's why I keep my portable compressor in the back at all times just in case I come upon a street race. Only problem it I always gotta tell the other guy that I need to pump up my tires so I can beat him and my compressor takes forever to get the tires to 100 psi. I'm talkin' like 1 hour per tire. So I always win, by default, since they are always too scared to wait around until I'm ready....

hahaha so for this theory, our engines is producing negative horsepower!!! Well, for base Vibes. 35 psi per tire 140 horse, -22 horse from the engine gets our 118 baseline

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Re: Tire pressure 34 psi vs 32 psi (NibCrom)

Postby Ol' Timer » Sat Oct 11, 2008 11:32 am

Quote, originally posted by NibCrom »
I put 32 all around. I get my best mileage that way and it's worry-free.

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Re: Tire pressure 34 psi vs 32 psi (jake75)

Postby stealth » Sat Oct 11, 2008 9:31 pm

Quote, originally posted by jake75 »
I know that over inflation is not recommended for tire wear and handling reasons. My question is whether a minor overinflation to 34 psi would be an issue. I have these Tire Pressure monitor valve stem caps that are 34 psi I would like to use.

I wouldn't consider 34 psi overinflated if the the placard recommends 32 psi and the tire sidewall indicates a max of 44 psi. Go for it!

My tires are at max sidewall 44 psi. The ride is a bit stiffer but I think the psi is helping me get better MPG. I've had no problems with handling on wet or dry roads. Also my elderly mother and grandfather haven't complained about the ride so it can't be that bad.

I'm not suggesting that anyone else choose max sidewall psi for their tires. I've done a lot of research and am comfortable with my decision for my car & tires.

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Re: Tire pressure 34 psi vs 32 psi (stealth)

Postby 1oldbanjo » Mon Oct 13, 2008 4:55 am

So what kind of tread wear mileage are you guys getting when you over inflate your tires to 44 or 47 psi. I know you will be wearing out your tires in the center of the tread way too soon - as the tire won't have a proper contact patch and will be putting too much force on the center of the tread. Your traction will also be reduced as a result of the reduced contact patch and both your ability to accelerate without spinning will increase - but worst of all your stopping distance will be increased dramically in an emergency situation when the maximum traction is required.

I have worked at a tire retailer and I used to be an avid autocrosser. When autocrossing we would increase our tire pressure slightly above the standard 32 psi when racing to help reduce the tire rolling over onto the sidewall during hard cornering. We would put a white mark with chalk or shoe polish on the sidewall of the tire and a bit of the edge of the tread. After a run you would check and see how much shoe polish was gone. If you had too much roll over and the white was rubbed off the sidewall you would add a pound or two - if the white was still on the tread edges you might take a pound or two out of the tire. Most of the time 36 or 38 psi was plenty - anyone that puts more than a couple of pounds extra is flirting with trouble and compromising the performance of their car and tires.

I have 225/45-17 Kumho tires on my Vibe and I keep 30 psi in them, When you increase the tire width you actually need to decrease the tire pressure to compensate for the larger footprint and greater contact patch under the car. I got 33.4 mpg at 70 mph on my last 300 mile trip, the tires are wearing evenly across the tread and they provide great traction. These tires are rated for 1,477 pounds each at 50 psi - which is a total of 5,908 pounds. The weight I found listed for the Vibe is 2,700 pounds and the combined carge weight maximum for passengers and luggage is 850 pounds which totals 3,550 pounds. This is 2,358 pounds less than the maximum load rating for the tires at 50 psi - so unless you are illegaly overloading your Vibe with a ton (2,000 pounds) of exta cargo you should not be inflating your tires anywhere near the maximum rating.

Please - before anyone puts more than 36 psi and overinflates their tires - go talk to your tire dealer and get some informed opinions. The 32 psi that is listed on my door panel for my Vibe is the number that is proven by Pontiac/Toyota to work best with the original 205/55-16 tire for the best combination of maximum traction, smooth ride and best performance. If you overinflate your tires you will get skittish handling, longer stopping distance, rougher ride, less tread wear in the center of the tire and a bit more mpg. If you underinflate your tires you will get less mpg, increase tread wear on the outside edges. poor handling as the sidewalls flexes and a smoother boatlike ride as long as you don't hit a pothole and break a rim or tire sidewall.

I don't think it is unsafe to experiment with pressures between 28-36 psi when you are choosing different tire diameters and widths - but anything above or below that is probably unsafe.

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Re: Tire pressure 34 psi vs 32 psi (1oldbanjo)

Postby stealth » Tue Oct 14, 2008 12:07 am

AGAIN … I’m not suggesting that anyone else take their tires to max sidewall psi. This is what I have chosen for the tires on my Vibe.

The San Jose police dept has been running their patrol car tires at 44 psi [max sidewall] since 1999 because safety & handling is improved at that pressure in emergency situations.
http://www.officer.com/web/onl...27281

I haven’t found any reliable source indicating that max sidewall is either “over inflated” or unsafe in any way.

[QUOTE=1oldbanjo]what kind of tread wear mileage are you guys getting [at] 44 or 47 psi. I know you will be wearing out your tires in the center of the tread way too soon [QUOTE]

I’m not trying to start an argument, but how do you know my tires will wear out too soon in the center of the tread? For about 35 years I have been maintaining tires at the placard psi as instructed by my father the mechanic and every set of tires has worn along the outside edges of the tires similar to the photo linked below. Those tires were kept at 32 psi as recommended by Toyota on the placard. L
http://techno-fandom.org/~hobb...r.jpg
I’m betting that psi higher than placard will result in more even tread wear.

[QUOTE] Your traction will also be reduced as a result of the reduced contact patch and both your ability to accelerate without spinning will increase - but worst of all your stopping distance will be increased dramically in an emergency situation when the maximum traction is required.[QUOTE]

This doesn’t make sense to me from a physics standpoint. There is less contact pressure per square inch and therefore less traction with lower psi and a larger contact patch. With higher psi the contact patch is smaller with more pressure per square inch and therefore more traction. The San Jose Police Dept has found that emergency handling is improved at 44 psi. I defer to their experience since they encounter more emergency situations than I.

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Re: Tire pressure 34 psi vs 32 psi (stealth)

Postby 1oldbanjo » Tue Oct 14, 2008 7:18 am

Stealth:

Cars driven at speed need higher pressure to perform properly - daily drivers will perform better and get better tire mileage with normal pressures. Here is a link for the increase in pressures related to high speed driving. You don't need pressures over 38 psi until you get to speeds above 130 mph.

http://www.tirerack.com/tires/...id=72

Excessive wear on the outside of the tire will occur with underinflated tires - or with spirited driving around freeway ramps. As I indicated earlier 36 - 38 pounds will generally correct that problem - however if you continually drive in an aggressive manner around corners you can count on wearing your tires edges out as they will be scrubbing around the corners. Here is a link for tire pressure during competition - notice that most pressure recommended are below 40 psi and that they state that tire pressures should be returned to the normal pressures when returning to the street. These pressures will provide the best traction and handling on dry pavement - pressures can be increased in wet weather to help avoid hydroplaning.

http://www.tirerack.com/tires/...id=58

I know that you will experience excessive tread wear in the center of the tread by running higher than normal pressure from my experience, from the recommendations of the manufacturers, and from having worked at a tire dealer. Here are some links for overinflation:

http://www.tirerack.com/tires/...hid=1
http://www.goodyeartires.com/kyt/maintainingATire/
http://www.wheels.ca/article/415271

Overinflation reduces the tire contact surface and requies a smaller area of tread to endure the imposed loads during acceleration, cornering or stopping- and the forces on the smaller footprint exceed the available traction sooner than a tire that is properly inflated and has a larger footprint. If you don't believe that overinflation reduces your traction during severe stopping or acceleration find a vacant parking lot or road and drive 60 mph and stomp on the brakes to reach the limit of traction at 60 mph with 44 pounds of air in your tires and mark the place you come to a full stop - then repeat this test with 36 psi in your tires. Repeat this when accelerating away from a dead stop and see what happens - I bet you can leave a long skinny black mark with 44 psi in your tires and a shorter wider black mark with 36 psi.

I really don't consider this to be an arguement - but I really don't believe it is good for the average driver to be putting more than 36 psi in their tires. Police officers who may need to drive in a high speed persuit may very well be in need of higher pressure than those of us who are driving 45 - 65 mph on our way to work (especially when it may be raining during the persuit and they need to avoid hydroplaning). I have a considerable amount of experience driving autocross and track events and I know that tire pressures near 36 psi will provide the best peformance - and tire pressures around 30-32 will give the best tread mileage during normal driving. I have worked at a tire dealer and I do the maintenance on our company vehicles and I have seen the effects of over and under inflation. The tires that are ignored and run underinflated wear the outside of the tread - and the people that read the maximum pressure rating on the sidewall of the tire and overinflate their tires wear out the center of the tread. This is especially common in pickup trucks where the maximum pressure rating for a loaded tire is used - and then the owner drives his truck around without any loads in the back.

So....that is what I believe after having owning, racing and working on my cars for the last 36 years (I am 52). I was once very much into racing and speed....then I got married moved to the country and bought a farm.....I don't have a "need for speed" like I used to. This is a picture of the last performance car I built and raced and it was a 1970 Porsche 914/6. It had a 3.5 liter twin plug 6 cylinder motor from a Porsche 911 race car that ran in the Portland, Oregon area, 9" wide tires, slicks, and weighed about 2,100 pounds ..... it was about 340 HP and would do the quarter mile at 12.95 seconds and 113 mph - top speed was about 145 with the gearing it had and it would get their really fast......and it had about 30 psi in the tires!


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Re: Tire pressure 34 psi vs 32 psi (1oldbanjo)

Postby jake75 » Tue Oct 14, 2008 10:41 am

I started all of this as I wanted to use some Tire Pressure monitor valve stem caps that are 34 psi leftover from my PT Cruiser days.

These cap indicators don't go from green to yellow until about 4 psi under - so I think I will use 32 psi and these 34 psi caps which supposedly will then warn me if the pressure goes below 30 psi.

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Re: Tire pressure 34 psi vs 32 psi (1oldbanjo)

Postby Sublimewind » Tue Oct 14, 2008 9:46 pm

Quote, originally posted by 1oldbanjo »
Stealth:

Cars driven at speed need higher pressure to perform properly - daily drivers will perform better and get better tire mileage with normal pressures. Here is a link for the increase in pressures related to high speed driving. You don't need pressures over 38 psi until you get to speeds above 130 mph.

http://www.tirerack.com/tires/...id=72

Excessive wear on the outside of the tire will occur with underinflated tires - or with spirited driving around freeway ramps. As I indicated earlier 36 - 38 pounds will generally correct that problem - however if you continually drive in an aggressive manner around corners you can count on wearing your tires edges out as they will be scrubbing around the corners. Here is a link for tire pressure during competition - notice that most pressure recommended are below 40 psi and that they state that tire pressures should be returned to the normal pressures when returning to the street. These pressures will provide the best traction and handling on dry pavement - pressures can be increased in wet weather to help avoid hydroplaning.

http://www.tirerack.com/tires/...id=58

I know that you will experience excessive tread wear in the center of the tread by running higher than normal pressure from my experience, from the recommendations of the manufacturers, and from having worked at a tire dealer. Here are some links for overinflation:

http://www.tirerack.com/tires/...hid=1
http://www.goodyeartires.com/kyt/maintainingATire/
http://www.wheels.ca/article/415271

Overinflation reduces the tire contact surface and requies a smaller area of tread to endure the imposed loads during acceleration, cornering or stopping- and the forces on the smaller footprint exceed the available traction sooner than a tire that is properly inflated and has a larger footprint. If you don't believe that overinflation reduces your traction during severe stopping or acceleration find a vacant parking lot or road and drive 60 mph and stomp on the brakes to reach the limit of traction at 60 mph with 44 pounds of air in your tires and mark the place you come to a full stop - then repeat this test with 36 psi in your tires. Repeat this when accelerating away from a dead stop and see what happens - I bet you can leave a long skinny black mark with 44 psi in your tires and a shorter wider black mark with 36 psi.

I really don't consider this to be an arguement - but I really don't believe it is good for the average driver to be putting more than 36 psi in their tires. Police officers who may need to drive in a high speed persuit may very well be in need of higher pressure than those of us who are driving 45 - 65 mph on our way to work (especially when it may be raining during the persuit and they need to avoid hydroplaning). I have a considerable amount of experience driving autocross and track events and I know that tire pressures near 36 psi will provide the best peformance - and tire pressures around 30-32 will give the best tread mileage during normal driving. I have worked at a tire dealer and I do the maintenance on our company vehicles and I have seen the effects of over and under inflation. The tires that are ignored and run underinflated wear the outside of the tread - and the people that read the maximum pressure rating on the sidewall of the tire and overinflate their tires wear out the center of the tread. This is especially common in pickup trucks where the maximum pressure rating for a loaded tire is used - and then the owner drives his truck around without any loads in the back.

So....that is what I believe after having owning, racing and working on my cars for the last 36 years (I am 52). I was once very much into racing and speed....then I got married moved to the country and bought a farm.....I don't have a "need for speed" like I used to. This is a picture of the last performance car I built and raced and it was a 1970 Porsche 914/6. It had a 3.5 liter twin plug 6 cylinder motor from a Porsche 911 race car that ran in the Portland, Oregon area, 9" wide tires, slicks, and weighed about 2,100 pounds ..... it was about 340 HP and would do the quarter mile at 12.95 seconds and 113 mph - top speed was about 145 with the gearing it had and it would get their really fast......and it had about 30 psi in the tires!


NICE...!!!!

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Sublimewind
 
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Re: Tire pressure 34 psi vs 32 psi

Postby stealth » Tue Oct 14, 2008 11:28 pm

Quote, originally posted by jake75 »
I started all of this as I wanted to use some Tire Pressure monitor valve stem caps that are 34 psi

Jake, I hope those valve stem caps are working out for you!

1oldbanjo, none of those links had any info to compel me to change. I've seen that info before & I've made an informed choice with my car and my tires. I'm not trying to convince anyone to do what I've done.

On http://cleanmpg.com Xcel [Wayne Gerdes], Hobbit, Delta Flyer, and others are running tires at 44-60+ psi and experiencing even tire wear, extended tread life, and increased mpg.

best wishes

stealth
 
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