the car in my avator gave me fits on the spring rates--springs weren't what they were supposed to be--finally bought every spring in the chicago area ( about 30) and worked my way thru them--only took about 4 changes to get the car where it wanted to be---

also found the same issues with a late model dirt car I was involved with--several springs before the car is rite but then you can make changes and get preditabal results.

so when i built my last race car, I mounted the coil over exactly above the rear axle so the spring rate is the spring rate--not something multiplied or divided by some factor --