[JayG]

Originally Posted by SCCA_AX

I wouldn't sweat it too much, the RE-71R is pretty pressure agnostic. Start at 35-37 square. Too much pressure (40+) and they get a little too sharp / antsy. Too little pressure and they just burn off the shoulders quicker, but aren't really any faster or slower.

If you go further down the STR rabbit hole and start running lots of camber you can probably start dropping down to the low 30s, especially in the front, and see time gains. Gotta test though.

FYI, if the tires are brand new, they tend to take an event or two to really hit full grip. Street miles don't speed up this process. Then they're pretty consistent until the tread is almost gone, as long as you don't cook 'em at a track day.

Good luck.

Originally Posted by Anker

35-37 is way too high pressure to start with. Start with 34, do a run or two and watch whether the wear mark comes down to the small triangles on the sidewalls just inside the treads. If not, drop the pressure by 1 PSI and repeat. As the tire heats up after each run you will have to let out air to keep it at your desired pressure. Same pressure on all 4 tires.

If the track is hot (sunny and over 70 degree air temperature) the RE71-R will get greasy after 3-4 runs. You will need to get a garden sprayer with water and spray the tires to keep the temperature down.

If you really want to do it properly get a tire pyrometer and measure the tread temperature at the middle and each side of the tread immediately after each run. You want to temperature to be as even as possible across the tire. If the center is warmer than the outside edge your pressure is too high. Because of the limited camber of the Boxster suspension you will not be able to get the inside and outside temperatures to be the same. The outside will always be warmer.

Since this is your first autocross you will not be driving the car nearly as hard as experienced autocrossers, so don't let the pressure get under 30 PSI, even if the wear mark doesn't get down to the triangles.

Turning performance will improve if you change toe-in to 0 in front and maximize front end camber, but not more than a couple of degrees. On a stock suspension you will not even be able to achieve 1 degree camber.

Don't forget to add pressure to the tires before you drive home!

Have fun!

34 May even be too high to start
I typically would run 30-32 hot. So cold around 28