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

[jd66921]

Thanks for the replies!!

I ran 32/32 psi this week. The car seemed good, although not fast (need more
power!). It rotated well. If I kept my foot in it, I could get the rear to slide around
nicely. The hardest part is to keep my foot in it! Wear seems to be fine. I chalked
the tires and there was wear down through the treaded area but not beyond that, so
I guess I'm okay.

I wonder if I should drop the pressure more. In general, would grip increase or
decrease? I expect the curve should be bell shaped, pressure vs grip. I wish I
knew where the peak point is!!

Thanks!

Jeff