Formula 94 LT1

I am wondering in what years and exactly how the geometry was changed front and rear. So far all I can deduce is there was some sort of front control arm length change and a little less anti squat in the back in the later years. I would like a little more detail. Thanks

Solofast

The 17 inch cars went to "Zero scrub" radius front geometry. That is, they lengthened the lower arm to get the kingpin angle such that the steering axis went thru the center of the tire. They changed the upright and upper control arm too, but this was more to get the entire geometry package to work. This lowered the steering effort during hard conrnering, and made for less "kickback" in the steering.

It also, unfortunately increased the loss of camber at high steering angles and for this reason the earlier geometry is considered better for low speed, high steer angles, like you find in autocross.

In the rear, the tweaks were more subtle, less antisquat (different bolt hole height in the rear trailing arm bracket), and a different mount for the lower control arm bracket, and of course slightly different parts so that "mixing and matching" of the lower control arm brackets in the back will leave you with a poorer bump steer curve. Some have exchanged the trailing arm brackets to improve antisquat on earlier cars, but that's pretty much it.

Formula 94 LT1

What about the rear roll center? I heard somewhere that it was a little too high on the earlier cars and caused jacking in some cases. Also what programs are out there to simulate these setups for our cars?

Solofast

Yes, the rear roll center is lowered in the later cars, but I forget how much. As I recall it is some, but not enough to make a big difference. We had the parts and put in a complete 96 rear suspension on our 84 BSP car.. Hard to tell if it made much difference, and not sure either how much it shifts when the car is lowered...

We had an "in" and had our analysis done inside GM, so we never had a need to buy an analysis program..

Formula 94 LT1

Awesome info thank you. BTW were mounting points on the 84 different than the 96 or were the parts themselves the only difference?

ZR1 MK

[QUOTE=Solofast;1559015142]they lengthened the lower arm to get the kingpin angle such that the steering axis went thru the center of the tire. They changed the upright and upper control arm too, but this was more to get the entire geometry package to work. QUOTE]
Do you know the kingpin angle of the early and late suspension?

Formula 94 LT1

I was talking more about the rear pick up points and components.

Solofast

All of the 96 parts, as a package, bolted in. That was the only way it is legal in BSP. You aren't allowed to make modifications to allow updating and backdating. You could mix and match some of the parts, but the results were not good. For instance if you put the later lower bracket on the earlier cars, it all bolts in, but you end up (assuming you were lowered like a BSP car) right on the peak of the toe curve. That is, any movement up or down, resulted in more toe out. To live with that you would have had to put in a lot of static toe in and that would have made turn-in sluggish.

No, I don't know the difference in kingpin angles between the two. That would be interesting to know, since then you could calculate the difference in camber loss with steering angle. Bet you would be surprised how much it is.

DREGSZ

Zero Scrub came in in 1988, mid year I believe but not certain

BrianCunningham

Rear knuckle is different in the 96's.