Quote:
Originally Posted by ZDan
I don't agree with the "low as you can go" approach to tire pressures...
And anyway, there's no definite point of transition between "sidewall is not rolling over" to "sidewall is rolling over". Radial tires are very stable over a fairly broad range of pressures. Also this may be a recipe for running too much pressure for under-cambered cars, and too little pressure for cars with track-appropriate 3-4 degrees front camber.
For most of our cars, there's going to be a quite broad range of pressures that will perform well, IMO there's no reason to try to find the lower limit.
You can invest in a pyrometer and try your best to get actual representative hot temps, but then you still have to correlate that back to what is the best temp distribution across the tread for quickest times for your car.
Or you can just run 34-36psi hot pressures and not worry about it any further, for 99% of us that's going to be close e-damn-nough...
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Like you say, for 99% of people this is good enough. 99% of people also dont bother learning or trying new things, so there's that. Like I said, I dont do autocross, so this is more of a track approach. But with pyrometer in hand and timing every single lap and a datalogger to look at speeds and lateral forces thru the corners and a decent butt dyno, here's what I found:
- The 200TW "cheater tires" like the RE71R, A052 and rival S always overheat, there wont be a point where you wont be able to get enough temperature on the tire, on the dry.
- There is a clear point where you can clearly feel the tire rolling over, its not progressive at all, 1psi higher the car feels awesome thru the turns, 1 psi lower and the car feels like a boat after initial turn-in and is much harder to settle.
- The lower the pressure, the faster I went, but sometimes I would need a second or third lap to get ideal temps on tires, all depending on pressure and ambient/track temps.
For my last few set of tires, all of this on 17x9 +35 wheels, -4.7F/-3.0R camber and 0F/0.05R toe (toe-in rear) and on teh same day (70F ambient temp, dry and humid):
- Yokos A052 235/45R17: Fastest times were on 31PSI up front, 30PSI on the back, hot pressures. At 30PSI on the front, the tire rolls over mid corner on certain sections of the track and becomes squetchy drive and a few tenths slower. Higher pressures were also slower, at 34PSI up front the car felt better, but was slower ultimately, almost a full second on a 2min track.
- Nankang AR1 235/40R17: Fastest times were at 29PSI up front and 28PSI on the rear. Lower than that the tire was very hard to drive, it felt as the tire was about to come loose from the wheels. These tires took 3 laps (including outlap) to heat up properly at this pressure. Higher pressure made them slower, about 1.5 seconds slower at 36PSI (that was as high as I went, no point in going higher on these). They were also about 1 full second slower than the yokos.
Now do with this information what you want, flush it down the toilet for all I care, but I just want to point out that the "as low as you can get it" statement from me came from my own personal data gathering. I have been bitten on the ass many times already by trusting what "experts" or "experienced" people say.