Tire Pressures

[Vytenis]

Porsche provides tire pressure recommendations. What do you run on the street and autocross.  What are the symptoms at autocross if pressure is too high?

[Hammerin Hank]

Vytenis wrote:

Porsche provides tire pressure recommendations. What do you run on the street and autocross. What are the symptoms at autocross if pressure is too high?

I've found this to be a good read on the topic. http://www.autocross.us/forums/lofiversion/index.php/t46.html

For my FWD Nissan, I run 36f/32r for the street and bump the fronts up to 38 for driving events with street tires, leaving the rears at 32. With r-comps I run 32f/26r, track only, of course. If it's really cold or wet, I'll take the pressures down 5-6 psi, all the way around.

The symptoms of too high a pressure will be loss of grip/traction, which is the opposite of what you want. Unfortunately, under inflation causes the same symtom with the addition of possible tire roll under. The tricky part is to find the sweet spot some where in between. What makes that even more complicated is the variables that get thrown into the mix. I.e. air/track temps, weather, type of tire, tire model/manufacturer, your suspension setup/tuning or lack there of, driving style. It's a moving target, in other words. About the only real way to dial in the optimum for you, is by trial and error.

[Vytenis]

Thanks

[betegh9]

V,
Another way to get proper tire pressure, is to chalk the side walls of the tire, make a run and see how far up the sidewall the tire has been scrubbed. Most tires have a tire wear mark indicator or arrow. If you reach that spot, great. if you rubbed too high on the sidewall, the tire is rolling over to the sidewall and therefore the pressure is too LOW. If you are scrubbing just on the flat part of the tread, you have too much pressure. On cold days, tires will be cold and traction will be NFG, so you want to run as low a pressure as possible to scrub some heat into them. on hot Summer days, the tire will oncrease in pressure all by itself, so you want to check pressures after every run, and adjust according to the behavior of the car and how far you are scrubbing up the sidewall.

after about 5 years of AXing, you might go to an event and know what is the right pressure......that is if you do not change tire manufacturers. Unfortunately, if you WANT TO WIN, you have to show up with the BEST tires possible, and every year, manufacturers are making better and faster tires. Today, the best AX tires will run about $1200.00 for a Porsche GT-3 or 997, and will last about 50 AX runs (6 events). That's $25 bucks per run plus the entry fee. Older models that use smaller tires will cost a bit less.
In America......if you want to have fun, and win, it costs $$$$.

Happy motoring!