Im looking at buying some BC Racing Coilovers and I want to switch the spring rate to something for street/drag, that'll keep my back end from equating so hard and causing front wheelspin. Anyone have spring rate information for this?

 

Squatting is not the cause of front wheel-spin. Lousy shocks and a center diff that isn't locking hard enough are your problems.

 

Why would it not lock hard enough?

 

If you are spinning both fronts, then your center is not staying locked, so it isn't locking hard enough. However, if I misunderstood the question and you're spinning just one front, then you need to either fix the suspension or swap the front helical for a clutch-pack. But even if it is the suspension that's to blame, raising the rear rates is probably not the answer; shocks make more of a difference.

 

Both front tires are spinning when I 2 step launch

 

Center diff, then. What mode do you have it in?

Of course, some folks might say that an X with a hard-locking center is an X about to eat its transfer case, so a better suspension is still a good idea. My main point was simply that preventing the rear from squatting isn't the key as it won't do much for front grip. Better front shocks is the answer.

 

you actually want the rear to squat and softer rear shocks help with "wheel hop"

the front tire spin could be front diff related as IOWA999 mentioned

 

You'd be better off contacting STM about the D2/custom swift spring combo I have for my X. It's setup specifically for drag racing.

 

Is there no limit to your knowledge?

 

I half agree. I agree that you want some squat, for two reasons. First, if the suspension isn't helping to absorb the shock of the initial launch, then tires are more likely to break free. Second, to the extent that the rear squats more than the front rises, you are lowering the CG and transferring less weight to the rear. In a dream world, you transfer only enough weight to get the weight distribution near 50/50; any more and now the front end is too light; any less and rears might now break free. Of course, how much weight is transferred depends on acceleration and CG height, the first of which you are doing all that you can to maximize. So, if you transferring too much weight to the rear (which is very likely), then the most that you can do in this area is lower the CG (or shift it forward).

As to the driveline and tire-spin, the first question to ask (even if I waited until a second or third post to do so) is whether one or both front tires are spinning. If it's only one, the front diff isn't doing its job, so you consider getting something that locks harder than a helical. If both are spinning, then you look at the center diff, instead, since it's the center that is allowing the front wheels to turn faster than the rears.

The first fix might be as simple as changing S-AWC mode. You also might get a better program for drag-racing, as in one that locks the center harder than the OE program's maximum. Another trick here is to get what some call the Tommi Mak pressure switch for the ACD/AYC pump, which gets the pump to store a higher pressure, such that the same solenoid duty cycle ends up producing more lock.

Another cheap first test would be to dump the KYBs and pick up the suspension off an MR. Billies pwn.

 

Good info here!