General info for an uneducated AX'r, Primarily tire pressure Options

[jd66921]

Hi,

I've been doing AX's for a little more than a year.

Currently I'm driving Howard's old car "Suzi". She's a pretty much
stock 914 2.0l. She's been lightened a little. She has fiberglass hood and
bumpers. All her heat and ventilation has been removed. Weight is 2050 lbs

The engine is a stock 2 l as far as I know, and has an unmolested MPS.
The transmission is stock.

I do not know what kind of shocks are on her. The rears are yellow and do not
seem to have any adjustments. The rear springs seem fairly soft to me? There
are sway bars front and rear, I do not know what size they are. The fronts are
adjustable with a number of holes in the horizontal arms. They are set to the center.

I typically run about 10-12 seconds behind Corvettes, A Birkin, and a well
setup Mustang Cobra. I am typically 3-4 seconds behind set up Miata's,etc.
This is on courses that I would generally say favors the high powered cars.
Generally, the courses are two 180's at each end, fast stuff down the middle,
and most of the courses I can take flat out or with minimal lifting., except for the
real corners, of course.

Wheels are 5.5 inch Fuchs, with Falken Azeni RT-615's.

My big questions is: I am now running 25 psi front and rear in the tires.
Is that in the right ballpark? Should I go higher/lower, and why? The car
feels good most of the time, with a little bit of mostly controllable oversteer. I
can get some wheel spin off the line, and a little on right hand sweepers.

What will changes to the front swaybar make? I've never understood them! I
would prefer an answer like "increasing the front rate will increase grip" instead of
"decrease over steer".

Anyway, I seem to have reached the limit of my improvements without help, so
I 'd like any help I can get!!

Thanks,

Jeff




My first question is

[Richard Casto]

I have autocrossed with the Faklen on my Civic. I would agree on the tire pressures mentioned here (high 30's or close to 40 as a starting point). Tires will have optimal grip within a range. Go higher or lower and you will loose grip. Lower than optimal typically result in a more predictable loss of grip when it goes away. Higher than optimal may result in a quicker loss of grip. Depending upon your car setup, driving style and how good you are factors into deciding what direction you want to go with respect to purposely using too high or low pressure in a tire.

For me with the Civic I would typically run higher pressures in the front (close to 40) and lower pressure in the rear (low 30's). I used lower than optimal in the rear to both reduce rear grip relative to the front (to help rotation) and to help create a predictable loss of grip (to allow me to catch the car when it would try to snap oversteer).

Your setup for the 914 will be different because it's not a front wheel drive car, but non optimal pressure should have the same general affect on a per tire basis. Again, don't use front wheel drive setup on a rear wheel drive car. I would also agree that any dramatic off course you had previously is not due to tire pressure issues.