Quote:
Originally Posted by mahout
Hold on. we're talking about the changes in behavior with pressure on any given tire. There is a huge difference between not only different brands but also the lines within brands. But in general - and thats all we can do here - the maximum cornering and mpg occur near the maximum pressure 'allowed'. Tire wear is maximized near the manufacturers recommendation.
That maximum handling pressure depends on the wheel width as well as the profile. I, too, run 40 profile tires, 205/40x17 on 17x7 rims. My street pressures are 40 front and 36 rear. Whenever the rim width exceeds the bead width, as it does in this case, additional pressure is needed to just have the tread lay flat on the ground. That way I get acceptable life out of the tires while getting good handling thanks to the stiffer sidewalls.
Running 45 psi in a 55 series stiffens the sidewall to get pretty much the same handling as 40 psi in wider tires on a wider rimbut at the cost of less tire life,. (thats why SS racers increased pressure; a stiffer tire is more responsive and deforms less which is necessary for road racing.)
A quick survey here shows the 4 of us have used more than 10,000 tires in the last 40 years in both racing and street use. We all agree that for maximum performance, braking, cornering, and mpg, pressures higher than 'recommended' are better; for maximum tire life pressures a little less than recommended is better. Tire life is opposite of mpg.How much above and below 'recommended' is indeed different for each tire,
Rolling friction is not just a result of hardening or surface contact. The materials and tread design are also heavy factors. The less a tire surface deforms when it rolls is the key to lowering rolling friction. Hardening and pressure contribute but the rubber composition and tread design probably have more to contribute. A tire with no deformation would yield less rolling friction but would be a tad difficult to turn or shed water.
PS the general rule for altering pressures on tires is when the rim width exceeds the 'nominal' rim width the pressure shouldd be increased to get the tread' flat. when the rim width is less than the 'nominal' rim width the press ure br reduced to get the tread 'flat' The nominal rim width, or presumptionally the bead width, can be found in TireRacks specifications data.
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Your street pressures are very close to what I would reccomend as well
Our opinions are only separated by a couple of pounds on this issue and that can be easily attributed to tire brand and car setup. With that said, am I to understand that your street pressures represent what you believe to be a happy medium between MPG and handeling? or just Handeling?
Ok, but as far as sidewall max goes that number shouldn't even be relevant other than ensuring you arn't exceeding it for safety reasons. Using a precentage of that should only be considered when refering to a specific tire.
Actually for the track I plan to use 38 front and 40 rear next time out, are you running a RSB by chance?