He all, I'm trying out different spring rates on my STR setup. I have two friends that are kindly letting me borrow their extra spring sets but there's a small difference in the rear set. I currently run Moton Club sports with Hyperco springs, 2.25" inner diameter on all 4 corners with Eibach helper springs. The current rear set is 700 lbs with a length of 7". The spring set I'm borrowing is a pair of Eibach, 2.25" ID, 550 lbs at a 6" length. I'm wanting to know around what length and spring rate would the coil springs start to bind against each other. I figured the lower I go in spring rate the more important free spring length becomes in regards to not binding. Should it be okay testing the 6" spring with a 550 lbs rate on Moton club sports?

As for reference I'm currently running 6" springs in the front at 850 lbs. I will be reducing the front springs down to 750 lbs but keeping the 6" length as any longer and the lower perch would hit the upper control arm.

 

It's going to be different per brand but you can use this for a reference.

http://eibach.com/eibach/img/ers-catalog-2004.pdf

 

Awesome, thanks for the catalog link. I found the numbers I needed and it looks like I'll be fine. For those viewing down the road the Eibach sheet says to look at the "Sc" measurement for deflection/travel available until the spring binds.

length.ID.rate
0700.225.0700 :: 3.53 inches deflection
0600.225.0550 :: 3.38 inches deflection

0.15 inches (~ 4mm) of less travel going from 750 lbs to 550 lbs and 7" to 6" free length.

 

After realizing the 4mm difference isn't the real comparison I needed I calculated the force it takes to reach binding on each spring.

Force = k * (D_standing - D_deflected)

length.ID.rate
0700.225.0700 :: 3.53 inches deflection
0600.225.0550 :: 3.38 inches deflection

700 lbs/in * (3.53 in) = 2471 lbs
550 lbs/in * (3.38 in) = 1859 lbs

0700.225.0550 :: 3.65 inches deflection
550 lbs/in * (3.65 in) = 2007.5 lbs (for a 550 lbs, 7" spring)