Nightcruzer

Okay, I've done my own engine work, rebuilt my entire suspension, redone my entire interior AND painted my own car, BUT WHAT IS THE PROPER AIR PRESSURE IN A TIRE? I shouldn't even be second guessing myself, but it is in the vicinity of the pressure listed on the sidewall of the tire, right? NOT the automobile manufacturer's recommended tire pressure. My reasoning is, when you go to aftermarket tires, the pressure is specific to tire not the car, as in moving to tires for 17" rims up from 15s. The 17s will have much higher pressure and running 32 lbs would destroy the tire AND rim. Am I right? I only ask because in the past month, I have had two different mechanics at two different shops tell me that I am absolutely wrong and I have actually had to intensely argue my point to the point of almost busting a vein in my head.

IROCKZ4me

Yer pretty much right on.
Tire pressure is more a function of tire design and the actual application. The tire placard that comes with the car ha the recommended tire pressure for the car with the OEM tires under most normal conditions. Change the type, brand, model or size of tire (or the intended use of the vehicle) from OEM and the best tire pressure may change. For maximum MPG run higher air pressure. For higher speed stability and maximum tire heat reduction run higher pressure. For quicker responsivness increase pressure. For increased traction decrease pressure. For maximum comfort run less. For maximum handling you may need to run different pressures on each axle or even each tire.

Keeping in mind that you asked about larger than stock diameter wheels and tires with short sidewalls, yes pinch flats and rim damage will occur easier at lower pressures. Running near max tire pressure will reduce the likelyhood of this type damage.


Some times you just gotta say "yeh, right, what ever you say" when dealing with run of the mill mechanics or shop workers.
Once a buddy had a "wheel alignment/suspension specialist" at an NTB tell him he should cut off the long things sticking up out of the top of the struts with a hacksaw because they were close to the hood. He was talking about the adjusters on a set of adjustable Koni struts.
Yeh, sure, I'll be sure to destroy a set of high rent adjustable struts dude.

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Tracy /AKA IROCKZ4me
'86 IROC-Z Camaro
"Cogito ergo zoom"

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[This message has been edited by IROCKZ4me (edited November 18, 2001).]

AlkyIROC

Sidewall pressure is the maximum pressure when the maximum load is on the tire. Sidewall pressure usually says 35 psi.

Typical radial tires with normal loads on them work best around 32 psi.

Get some tire chalk (white grease pencil type). Go to a parking lot when it's empty. Make a heavy line across the tread then drive a short distance across the parking lot. Get out and see where the mark is worn off the tread. On the edges means the tire pressure is too low. In the center means the tire pressure is too high. Don't try doing a burnout or anything. Just a nice gentle straight line drive.

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IROCKZ4me

That is true for most 15 inch tires, but for most 16" or larger tires, and nearly all "V" rated or higher tires it is 44 PSI. These tires tend to have flatter (less curvature side to side) tread and straighter sidewalls and tend to work better between 38-44 PSI

ChillPhatCat

What is written on the tire and what you should run ARE TOTALLY DIFFERENT... If it says max pressure 44 DON'T INFLATE TO 44!
The max I'd run on any tire is 38 PSI... In general, 32 is the universal pressure, I would start there and go up or down from there depending on what I wanted to do with the car, but no real out of the ordinary wear will result as long as you stay within reason.

nicmike85

There is only one correct tire pressure for a specific tire on a certain car. By this I mean you will find out how wrong you are when your tires prematurely wear out. The manufacturer recomendations are real close. As for tire and wheel changes it should not very real far as long as the vehicle weight is not changed drasticaly. The chalk idea from Stephan sounds like a good starting place. Then periodicaly check tire wear and adjust accordingly.