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      04-09-2008, 03:22 AM   #19
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Drives: 三三五i
Join Date: Aug 2007
Location: CA

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Originally Posted by MrSteak View Post
The recommended tire pressure (either from the car’s manufacturer or the tire company) is shit. The numbers they give you are pretty much only for comfort. (Not performance, safety, or longevity)

You’re not “over inflating” your tires, you’re inflating them to the psi that gives you the best overall use of them, whether it be for performance OR safety.

With max psi and above you have:
1. Stronger sidewall
2. Better contact patch
3. Longer Tread life
4. More contact/traction in wet weather. (The faster you go the better contact your tires will have with the roads opposed to using the manufacturer’s recommended psi.)
5. Better handling
6. The only downside to this is a harsher ride... thats all.

I've learned from racing instructors and all, but taking a stunt driving course opened my eyes to all the little things about tires. I learned a lot about tires, and a lot about cars and handling in general, so I’m just throwing my 2 cents in. Obviously you can’t inflate your tires to 50psi and start doing stunts in your E90, but I took this course, learned a lot, and will ALWAYS keep my tires inflated to at least 5-10 above max psi.
I disagree on some points. I agree that manufacturers often state specific pressures for comfort. Hence, I don't follow them. The more a tire is inflated, the "stiffer" the sidewall is per se. It doesn't make it stiffer, but there is simply less roll over when the tire is loaded. But it does act like running a tire with a stiffer sidewall.

I have experienced many "over inflations" where the tire is inflated to the point that the contact patch is reduced because the tire starts to get ballooned. Try this... Inflate your tires to 10psi over the max stated rating on one side, and 5psi under the max rating on the other. Put a stripe of paint on the tread of all 4 tires, from inner edge to outer edge. Take a quick drive on the freeway (less than a mile), and take a look at the paint stripes on the tires. The ones which are inflated higher will have a lot of paint left on the insides and outsides of the tire due to the ballooning. The contact patch of the tire is reduced, and braking performance is worse.

It is better to run slightly higher pressures tires in the rain, as it reduces the contact patch on the road, which reduces chances of hydroplaning. It's like driving on 315mm tires in the rain vs 225mm tires. Even though there's less contact patch, there's a huge reduction in hydroplaning because there's simply less surface area for hydroplaning.

I also find better cornering performance with more pressure in the tires, up to a certain point. Once there's a lot of air and the tire is ballooned up too much, there's too little contact patch on the road for grip, even though there is hardly any rollover because there's a lot of air in there. I try hard to find the balance between the two conditions at the track. Since I'm usually autocrossing, braking performance is not quite as important as on the track so I don't mind sacrificing some braking and accelerating grip for cornering.

Harsher ride and wear... true but not the most important to me. Performance and safety above all.

A lot of stunt cars run very high PSI because they incur a lot more load than a typical car does. Driving on 2 wheels and jumps are some things I can think of. Also, if doing a lot of J-turns and drifts, it's best to inflate really high to minimize the tire from rolling over and scrubbing all the tread off the sides of the tires... They would wear VERY quickly if inflated normally.

In the end, do what suits your driving style best. It's just in my experience, I have not had the best performance by inflating the tire so much.
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