Hey gang, I know this is a little bit of a reach, but I purchased these Cooper Challenge coilovers, and while the dampers are GREAT, the spring rates are just too high for autocross. I want to order some replacement coils, but the numbers are worn away so I don't know what diameter and length I need. Can anybody tell from the picture or give me a direction to go finding out?

 

Blue springs may be Hyperco's, if so, older Hyperco's had the spring rates engraved on the flat area at the end of the spring. The red-ish springs may be Eibach's. I suggest you take all the springs off and measure their uncompressed free length, inside diameter and use a caliper to measure their wire diameter, then call both companies and give them the info and they may be able to give you the spring rates. Springs are probably 60 mm ID or 2.5 inch.

What tires do you think you will be autocrossing on because to some extent that will determine what spring rates you will want?

In STX class I prefer to run softer springs than some other people, apx 285 to 350 lbs in front and 342 to 400 in the rear. What spring lengths you will want will also be determined to so extent by the rate you run. Lengths in the rear are less critical than the front, where tire clearance between the spring perch and tire may be an issue. For length in rear you will most likely want something between 140 mm (400 or higher rate) and 8 inches (285 or Softer) I prefer something in the 170 mm to 7 inch, in the rear.

Most people, it seems, prefer 6 inch springs in front. I would only recommend that length if you are using at least a 400 lb spring. If you have 60 mm ID springs you may want to to get 170 mm length. If you have short stack tender springs and using 350 to 285 lb springs you may be able to run a spring as long as 7 inches, without creating much of a tire clearance issue.

Spring rates should be matched to the shocks as well, so find out what rates they were designed for or get them re-valved.

 

It is also possible all the red springs are H&R and the tenders on the rear, to be a short stack.

 

Thanks for the info! I plan on pulling one front and one rear off the car this weekend to disassemble and take measurements. The car runs in STX right now, and the past two seasons I've been on Bridgestones, but I think next season I may switch to the BF Goodrich. Home autocross is with WDCR at Fedex- looking at your profile, I'm gonna guess we know each other.. LOL