Rear Spring Rate

[66shortwide]

Anybody have a suggestion on rear spring rate for a 66 shortwide? I'm running c4 corvette front and rear suspension and am ready to buy my rear coilovers. Gas tank is behind the axle, battery behind the cab, motor set back 12" if that helps any. I was given a suggestion of 400 lb, but that seemed a little heavy - any ideas?

[robnolimit]

The IRS geometry adds leverage to the spring, appx 30%. If the back of the truck weighs 1400lbs, thats 700 per side. Hoping that you use a 5" stroke shock and a 12" spring, you will have appx 3 1/2" of static spring compression at Ride Height. 700 div. by 3.5 = 200 lbs/in, x 1.3 (for the 30% leverage) = 260. If using a 4" dtroke shock and 10" spring, add another 20% = 312 (use 300)

[Tony@AirRideTech]

Rob is right on.... keep in mind though he kind of gave you a formula... dont take those rates for instance and try it on something else. Keep in mind, if you get funky with your mountinging pick up points that adds leverage as well... if you shorten up the shock that changes things as well..... One of your best bets would be to simply order your coil overs through someone like Rob, give him all of your info and between my data and Robs knowledge we can get you extremely close without weighing it up... ultimately weighing it and measureing it up ourselves would give you best case outcome but Rob's pretty sharp

[66shortwide]

thanks guys - that was exactly the info I needed.