[Tony Curcio]

[QUOTE=
Do you have any input on the original question - does the cal tracs change the effective Instant Center of a leaf spring suspension?[/QUOTE]

CalTracs most definitely change the instant center. The rear attachment point (the one directly under the axle tube), is much lower so that the angle is more acute through the the front attachment point (the one below the spring-eye), in other words, pointing upward.

I have to agree with what Dinsdale said. In back to back testing on two different cars, we found the lower hole on the front mount resulted in less separation between body and wheels, as you would expect from a lower Instant Center. The resulting hit was softer, and that enabled the cars to hook on hot tracks. In better conditions, the upper front hole sometimes resulted in better 60 foot times, but it was not nearly as consistent. These were both automatics.

But what really made it work was finding the right shock setting. Controlling the rate of separation, as you already mentioned, is key, and ADJUSTABLE SHOCKS CAN POINT YOU IN THE RIGHT DIRECTION WITHOUT SPENDING MONEY. Don't assume that it's a harder hit that you need. Try going both directions with the shocks. If a stiffer shock (when extended) improves your 60 foot, then you'll know the IC needs to be lower. If a looser extending shock helps, a higher IC. It's also possible that the shock adjustments alone will be enough.