by Ishiftem » Mon Nov 09, 2009 1:04 am
Here is the deal with the rack dimensions. I have been running simulations on the computer, and the rack length is the LEAST important part of this equation for "zero" bump steer. The greatest factor by far is the inner and outer pivots. Leaving the height of the inner and outer pivots, the rack length is almost inconsequential. The difference between a 20" rack and a 23" inch is about 8/100 of an inch at 3 inches of dive. Lowering the outer pivot is the key. At it's stock height, with a 22 inch rack, the change in toe at 3 inches of dive is almost a Half inch. That's significant. Lowering it 1/2 inch brings toe change to .05 inches. That's nothing. So to make a long story short, Go with whatever rack in the 20 to 23 inch range works best for you(budget,availability, etc.) Install it so the the pivot heights are the same as stock. Then go get a bump steer kit from Sphon or where ever, and lower the outer pivot 1/2 inch. This will get you so close it will scare you. Make final adjustments on the car with the bump steer kit to achieve zero bump steer. This is with stock vega spindles. That's it folks, nothing to it. Figuring different spindle heights or adjusting ackerman is much more complicated. I'll need more time on that.
P.S. You could even go shorter on the rack. I wouldn't go longer tho. Also the stock crap if your interested toes out .43 inches at three inches of dive. Way to go GM
Any one can restore a car but, it takes a real man to cut one up.