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      04-09-2008, 12:11 PM   #22
Chowbow
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Drives: 三三五i
Join Date: Aug 2007
Location: CA

Posts: 6,703
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Quote:
Originally Posted by MrSteak View Post
Tires don't balloon up like you think. I used to think that way until this past September when I took a stunt driving class. The instructor (Bobby Ore) gave us at least two hours of classroom time on tires, which pretty much covered everything here, then throughout the course he showed us more... One thing I was surprised to see were the tires on his truck with a maximum psi rating of 44 inflated to 100psi. They didn't balloon, up, or get distorted in any way. (BTW, all the cars we used were stock.. even the truck.)

As far as wet weather traction goes... he explained how the faster you go, the middle part of the thread of a tire, bends upward into the tire. (Hard to explain half this stuff without him, or the tires/examples he used in class.) One example he gave was how he was working with a tire manufacturer and they'd have him drive over a piece of plexiglass with dye on it, and a high speed camera under it. At 70mph the tire inflated to a recommended psi would retain 70% of it's contact patch, where one inflated 5psi or so above max psi would retain 90%. (I don't know the exact #'s, but at each speed, the tire with recommended psi would retain significantly less contact than the one inflated higher, about a 20% difference.)

Don't get me wrong, this may or may not be the best set up for autocross, but for daily driving and everything in between I think it is. The stunt driving school was the most thorough driving school I've been to yet, and I plan to do more, and attend some more racing schools in the future.
I don't think you can see the ballooning, but do the paint stripe test and let me know what you find. It's similar to the plexiglass dye with a high FPS camera showing how the tread contacts the surface, but without all the high tech equipment. Alternatively, drive 20k miles with your tires inflated to say, 55psi and see if the center of the tire is much more worn compared to the sides.

I understand what you mean with the center of the tire moving up from the ground. It's like if you look at the contact patch head on, it'll kinda be like the shape of a "W" where the center section of the contact patch is elevated, and the tire is riding on the insides and outsides.

I encourage you to test on your car and see how things work for you. The stunt driving instructor may have his preferable settings, and you should try out the best for your car and your driving style.
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