Tire psi at the track for RFTs?

[persian54]

So what would be recommended as the cold and hot pressures for the rfts?

on the door, it says 42 cold rear, that is freaking hot!

42 cold will become 50 hot...

[ChuckB]

Wickedly simple question, wickedly complicated answer.

You are trying to keep the loading across the face of the tire even across the entire width of the tread, which should read by core tire temperature, and have enough pressure to keep the tire stable and not build up too much heat [so 42 starting may end up at 43 when hot], or have to little pressure [when cold] which will allow more tire flex, which will build up more heat and more pressure [39 cold may end up 45 hot]. Start with the recommended pressures and see what the car does, oversteer - increase the front, reduce the rear or the other way round for understeer. This is trial and error and is affected by track surface, tire tread depth, weather conditions. If you can find someone who's setup is the same as yours, then you can get a head start in getting the car to handle as well as it can, and balanced for your driving style while keeping tire temp even across the tread. I would add that you should never let the pressures get below or above the range specified for the tires.

[persian54]

Thanks for the advice

For me, I've gotten the pressures down (more or less) on my m3, but no idea on the z4, especially cause the cold psi is 42

When i ran a 38 cold rear yesterday, it went up to 45hot!

the front was 36 cold, 41 hot

dropped it down to R 36c, went up to around 42 hot
F 34 C went to 39 H

car handles relatively well, bit of oversteer though

[SANguru]

are you running nitrogen? Also did you check pyrometer? What's the temp?

Originally Posted by persian54

Thanks for the advice

For me, I've gotten the pressures down (more or less) on my m3, but no idea on the z4, especially cause the cold psi is 42

When i ran a 38 cold rear yesterday, it went up to 45hot!

the front was 36 cold, 41 hot

dropped it down to R 36c, went up to around 42 hot
F 34 C went to 39 H

car handles relatively well, bit of oversteer though

[persian54]

nope, not running nitrogen

[HerrK]

First the RFT's are good for 50 psi per the sidewall marking. Most passenger care tires RFT or Non RFT are good for about the same max pressure (generally 50 +/- 2 psi).

I found this to be a helpful article when my son started autocrossing. Unfortunately not sure how much is applicable since the RFTs are stiff as a wedding p... anyway. Well you get the point I hope. I stood on the sidewall of an unmounted RFT and it deflected less than 1/4" - that is stiff. I couldn't even deflect the tread in the circumferential direction. Hence the RFT cabability.

http://www.autocross.us/forums/lofiv...x.php?t46.html

Go out there and give it a try. I thinking about doing an autocross with the Z in Oct. Let us know if you discover any magic handling tire pressure settings with the RFT's.