Cal Club Autocross Forums

Short question - How do I remove Corner - entry Push?

94 Base, Koni Yellow Race, 700 Front, 375 Rear, Racing Beat Hollow front, No bar rear, Toyo R1R 225/45 shaved to 5/32, Max front caster.

Starting from the beginning - The car had corner-entry under steer to snap corner exit over steer. I started with
Front = 2.8 camber, max caster, 1/8 toe-out, 4 inch ride height. Tire pressure 35 psi
Rear = 3.5 -4 camber, 0 toe, 3 - 3.5 inch ride height. 375 lb/in spring, Tire pressure 35 psi
This was my first setup and I was way off.

So, I focused on the rear end to correct the corner-exit over steer. Two weeks ago, following setup-up confirmed that the rear end is really close. In addition, I played around with tire pressure. I started with 30 psi, and ended with 24 psi. The thinking for the lower psi is the lower sidewall and the squareness of the Toyo R1R.
Front = 2.8 camber, max caster, 1/8 toe-out, 3.5 - 4 inch ride height. Tire pressure 24 psi
Rear = 1.6 camber, 1/8 Toe-in, 4 - 4.5 inch ride height, Tire pressure 24 psi

The car was finally coming together. Able to keep on the power starting from the apex. My times were improving and was up there with Steve Bradford. Him and I both drove the car and we both felt the car was still pushing on corner - entry.

So after that weekend, and looking at the tires, I concluded to drop the front camber. So I used the following setup this past weekend.
Front = 2.1 camber, max caster, 1/4 toe-out, 3.5 - 4 inch ride height, Tire pressure 26 psi
Rear = 1.6 camber, 1/8 Toe-in, 4 - 4.5 inch ride height, Tire pressure 24 psi

Comparing the last two events, the last setup felt the most balanced, indicating I'm going the correct direction. In addition, it was the fastest I have been in the car. But still has corner-entry under steer, with a slight, very slight feel of push on exit. This is to be expected on concrete, which last weekend was. One might say that the setup is great for asphalt, but these pictures of the tires are really concerning. The right side is worse, and the front is horrible. it is quite clear that the outside of the tire is worn the most, but not the edge. I'm concluding not enough camber, but it could be not enough tire pressure, or something else.

Left Front
Right Front
Left Rear
Right Rear
Right Front Closeup


Any advise would be greatly appreciated.

Kraig Klippel wrote:Short question - How do I remove Corner - entry Push?

Quick answers are:
Lower the front end
Reduce front roll stiffness
Increase front track

I don't understand your ride height measurements. Normally for the front of a Miata you are in the 12" range.

not enough info to solve your problem.

too many variables changed between setups, no tire temp data, no quantitative car performance data. ...sorry.

Max Hayter wrote:I don't understand your ride height measurements. Normally for the front of a Miata you are in the 12" range.

Sounds like he is going off the bottom of the pinch weld. Regardless, I think Katy is better qualified than you to give STS Miata advice. }:)

General rule of thumb says that if the car is balanced in steady-state cornering but you are seeing effects in corner entry and exit, you'll want to look at shock settings. Make *sure* you're not hitting the bump stops, becuase they throws everything else out the window.

Jason Isley BS RX8 wrote:Regardless, I think Katy is better qualified than you to give STS Miata advice. }:)

:unimpressed:

Center of wheel to inner fender lip vs. rail to ground?

Could your front pressures be a bit low?

We've gone to zero front toe, our SST Miata has great turn in. We're at around 12.5" in front and 12.75" in the rear. Maxed out camber. 3 mm rear toe-in.

500/300 springs with cut down bump stops on Penske DA

Dunlop Z1's 36/33 ... going to start trying to lower the pressures. Unfortunately we're on 195/55/15's.

Mako Koiwai wrote: Unfortunately we're on 195/50/15's.

Do you mean 55?

When I was first setting up my car, I found there were substantial balance changes with alignment (specifically the front/rear toe settings). You might want to try a systematic set of experiments at a practice sometime. The front is
especially easy since you can adjust toe at a tie-rod end. As Marshall implied, the difference in tire temps taken at 3 places across the tread is a very powerful setup measurement. You want the whole width of the contact patch to be working for you.

Since I was trying to learn to drive the car at the same time as doing my setup, I found it very useful to get inputs from other drivers. There are lots of folks around Cal club who have experience with miatae. Get them to drive your car at a practice and then ask them "what do you thing of the setup?" If several folks give you similar comments, you know you have an issue.

I figure that just because *I* make the car push on corner entry, it doesn't mean that *the car* has a corner entry push. ( It's taken me a while to learn how to "plant the nose" with braking so I've got the best grip at turn in. )

steve

To much front toe-out will cause corner exit understeer and bad tire wear. A properly set up car should have a touch of push on entry be neutral through the turn and have exit oversteer.