gkmccready

Anybody happen to know how much preload is typical in the stock C6 Z06 or Z51 springs at various ride heights?

Aaron Pfadt

Glen,

If by pre-load, you mean load in the spring at full droop, it is relatively low on a C6Z and C6Z51. They are different (due to different spring rates and factory ride heights) but I can tell you from having pulled a bunch of control arms off of stock sprung car, the load is pretty low. I generally release the load by pulling the upper control arm with a screw jack under the lower ball joint and then release the load by letting the suspension droop all the way out.

If you mean load at ride height, I can calculate that pretty well. If the corner weight is 850 (ballpark) the MR is roughly .4, the load in the spring is about 2100 lbs. That is independent of ride height. From there you can back calculate how much compression the spring sees by using the spring rate (530 lb/in for the C6Z) to calculate that the spring compression is just under 4 inches from it's uncompressed state. That is not completely accurate because the leaf springs are not completely linear in their rate, but it gives you an idea.

If the spring is lighter (ie from a base car), the amount of compression will be larger to achieve the 2100 lbs and therefore the pre-load at droop will be higher. The heavier the spring, the less pre-load you will have at droop to achieve the same ride height.

-Aaron

gkmccready

Thanks Aaron. That's pretty much exactly what I was looking for. Preload to me is how much load is left in the spring at full droop. I completely agree that the load in the spring is the same at ride height regardless of preload, assuming preload is less than the typical load a ride height, etc, etc. I'm still thinking of how droop/bump travel changes with ride height, and ride height is set my spring preload...

BTW, another thread here had the front MR for the leaf at .55 and the rear at .5 ... you're saying it's .4? I've also seen different MRs reported for front/rear coilovers. If the rain goes away I should measure it while the car is on jack stands...