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Racing tips, and other methods. Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 15 May 2002 15:51:21
In Reply to: max tire pressure vs. Saab recommended tire pressure?, Richard Dickinson, Wed, 15 May 2002 09:22:33 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The max pressure value on the tire is the highest pressure you can run safely. The higher the tire pressure, the more heat is generated in the tire, and heat kills tires. I don't mean reducing the tread life from 30K to 25K - I mean tread delamination and blowout. So it's just not a good idea to run a tire at it's max pressure. 6200 RPM may be max speed on the engine, but you don't want to run it there all the time.
Tire pressure is a balance between ride, handling, and fuel mileage. In general, less air makes for a smoother ride but sloppy handling, and higher pressure makes for a stiffer ride, better handling, and better gas mileage. There are limits - too little air and ride will suffer when the tire comes off the rim. Too much air, and the contact patch dissapears and handling suffers. BUT there are a few other factors.
You can run lower pressures if the car is lightly loaded. If it's running fully loaded (4 big guys and luggage, or a trunk full of cinderblocks), run higher pressure.
Tire wear is affected by pressure. Low pressure and the outer edges of the tires wear, but the insides don't. High pressure, and the inside wear while the outer edges get a free ride. You paid for the entire tread, you want it to wear evenly to get the best mileage out of the tire.
Try this old racing trick - take a piece of chalk, and run some lines from the tread up the edge and over the sidewall of the tire. Make a few lines per tire. Now, go for a ride, driving normally, taking a few off-ramps the way you usually do. Now, check where the chalk line has worn off. That tells you how much the tire is rolling over - essentially, are you driving on the sidewalls?
You want to use the whole tread, but not run onto the sidewall. If you're getting onto the sidewall, you need higher pressure. If there is any chalk left on the tread, then the pressure is too high.
I find 33 front, 34 rear give me good handling and ride. That's on a set of P4000's - different tires will feel differently. It seems to give a better on-center highway feel on my car.
Try that setting, and see how it feels. Then add a few psi and check the difference. Or less. All that matters is what you want. Monitor the tires for even wear across the tread. Draw a chalk line across the tread, and drive across a parking lot. Is it evenly worn side to side?
Frankly, just about any value between about 27 and 34 psi is fine. I don't like running too close to the max inflation value for continuous driving (autocrossing is a different matter). Since the rears are lightly loaded, you can run higher pressure in the rear, getting closer to the max level.
Good luck!
posted by 140.157.4...
, Wed, 15 May 2002 15:51:21 <-- Viewing This Message
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