Second Gen car with SPL rear lower control arms

[grippgoat]

Question for the 2nd gen owners with SPL arms on the rear. What shock mount hole are you using? Are you using a shock setup for a second gen car, or a first gen car?

Wall of Text:
I'm asking because none of the shock holes actually match the position of the hole on the stock second gen arms.

The stock arm is 450mm from the inner pivot to the outer pivot, and the shock hole is at 360mm from the inner pivot.

With the SPL arm set to 450mm, the shock mount holes are at (measurements are probably +/- a 1-2mm) 323mm, 345mm, and 368mm.

The motion ratio calcs for 323, 345, 360, and 368 (just hole position, not taking shock angle into account) are 0.72, 0.77, 0.80, and 0.82. That's 450/x.

I have written down that the 1st gen motion ratio is 0.76, which I think came from the Racecomp article on 2nd gen suspension changes. I don't actually know what the measurements on the first gen arms are.

But anyway, I'm pretty sure the holes in the SPL arms are designed to match 1st gen cars.

The differences in motion ratios might look small, but motion ratio gets squared in the calculation going from spring rate to wheel rate. The reason is because both the lever arm and the displacement of the spring change with motion ratio. I think it's similar with shocks, in that the leverage of the damping force and shaft movement / speed for a given wheel movement are both changed. Although I don't know if shocks care about wheels as much as they care about springs. :/

Anyway, I installed SPL arms, which I did very shortly after buying the car, before I really had much time getting to know the suspension setup. I have Karcepts MCS 2wnr, ordered by the previous owner for a 2nd gen car. I don't actually know if the valving is actually different from 1st gen. But they have always felt a bit off in the rear. Like under-damped in higher speed when the ride felt ok for the street, and if I turned the shocks up to control bigger body motions better, the ride got very harsh quickly, like low speed was too high. And also the compression clicks have always felt too sensitive. I tried a short stint on the outer holes, which felt like damping might be going in the right direction, but I had to turn compression down to 0 to get it streetable. I didn't unfortunately have softer springs to try and keep the wheel rate the same.

Maybe I'm over-analyzing. But I'm strongly considering changing my shock setup, and thinking about whether I'd be better off with a setup intended for first gen, because of the lower arms.

Thoughts?

-Mike