Basic newbie autocross question, Tire pressure Options

[jd66921]

Hi,

I recently started autocrossing my 914. I enjoy it a lot! The car is not really set
up for autcrossing, no sway bars, standard alignment, etc, but it is still fun to see
what I can do.

The tires I am running are Kuhmo street tires. I know they are not optimal,
but I am not ready to upgrade.

The issue is trying to optimize tire pressure. I know the 914 is a very light
car and therefore may not need a lot of pressure. I ran them originally at 35 psi.
That seemed okay. I ran them up to 40 psi, and while fun to slide around, it was
way too much! I am now running 32 psi, and I don't know if I should go lower or
not.

How does the pressure vs cornering curve go? I would think the cornering force
would increase with tire pressure up to a point, and then tail off. Any ideas what
the range should be? 25-35 psi? Higher? Lower?

I'm just looking for general guidelines. Tires are 195/50's on 5.5 inch fronts and
6 inch rears at the moment.

Thanks,

Jeff

PS: Autocross video

[Racer]

Stock pressure, under "heavy load" is 29F/R. In my old 914, I ran 30/32 or 30/30 F/R depending on course layout.

You might start by "chalking" the tire. Mark where the Tread meets the shoulder. If after the run all the chalk is worn off, add pressure. If its all still there, lower pressure. You should have some type of wear mark on the tire to help show how much "rollover" the tire is doing.

Realize too that pressures will change a bit with temp. Once you find a pressure that works for you, you may need to "add some" in the cold morning but let some out as your runs progress.

Hope this helps!