Coil Over Question

I have some QA1 coil overs that need stiffer springs, they have 2 1/2" ID springs, will 2 5/8" ID springs also fit?

It would give me a better chance at finding used springs.

I have 12' 200# springs and want about 250#

 

I wouldn't use them that way. They need to properly center on the collars. Have you weighed the car to see what springs you need? New coils are cheap and you will get very close to the right spring with some easy math.
Assuming the shocks were installed at the right height, you can weigh that end of the car and use that to calculate the right spring rate to compress the 12" springs down to ride height. Remember that you use half the weight on that end of the car.
If the rear axle weight is 900 lbs, deduct the weight of the axle (maybe 200 lbs) and divide that in half for the weight over one wheel. So, 350 lbs each wheel. If you need 1.5" compression from the 12" spring height, (to get a 10.5" ride height on the spring) it would require a 230 lb spring. (230 lbs for 1", + 115 lbs for .5" = 345 lbs wheel weight). Just divide wheel weight by the inches you want to compress the spring. 350/1.5 = 233

 

Scotty, thanks for the info. When I bought the springs I called Speedway and got similar advise. The car has IRS, I don't know if that threw the math off. The car sits about right now, but it's at max adjustment. Maybe it's a little low for regular driving.

 

Ideally you would corner weight the car with the springs off and get accurate weights.

Also, if you were to look at (gasp) Honda boards, you could probably find 2.5" springs easier. I know my Prelude stock springs are 2.5", 14". Fronts are progressive though. I can check the board I know if you want.

 

You can also get the springs straight from the QA1 website. The IRS shouldn't have messed up the math. You really need real world weight, meaning gas, passengers, all expected equipment and a cooler full of beer. It often takes a couple of tries. if you no your current rate and can measure the length of the spring at ride height, you can backward math the current weight and required spring, too.