I am needing help figuring up which custom spring height I need. I am going with this company ... http://www.bluecoilspring.com/

Current setup (stock v6)
Front, 420lb, free height of approx 15.16, approx compressed 11.00

Rear, 107lb, free height of approx 15.42, approx compressed 10.25

Wanting to go to
Front, 700lb, I can get free heights of 8,9.5,11,12 (11/12 are unpainted )

Rear, 175lb, I can get free heights of 8,10.5,13,15.

I am wanting the car to be lowered approx 1.25-1.375 from stock with the stiffer spring rates.
Can someone tell me which springs heights I need, or show me a formula so I can figure up what I need.

 

Hi Jay,

1st off, spring rates are measured at 1" compression- so...

If your stock spring is 15" tall, then it will be 420lbs @ 14" height if that 420 is correct. You are then compressed to 11" at ride height.

Figuring the rate needed is a crap shoot but I can get you close. Base on the distance of the wheel centerline from the pivot point (A-arm bushings) wanting to drop another aprox 1 1/4"-and the spring location being aprox half that distance away makes aprox 1/2 the drop (5/8" lower compressed)

Now- the 700lb is offered in 11" and 12" standing height (not compressed. The rate is almost double so you will compress almost half the distance of the stockers (again based if the 420 is correct- I question this because I am not certain myself and only have your info to base this on). Stock 420 compresses 4" to ride height, thus 700 should compress aprox 1 1/2 to ride height (erring on the cautious side) + another 5/8" for drop leaves you with aprox 2 1/8" compressed height needed.

Now go backwards from the diesired ride height of 1 1/4" lower than stock or 11'- 5/8" and you have 10 3/8" compressed height. Then add the compress value above (2 1/8") to the 10 3/8" and you total 12 1/2" standing height- "This is conservative AND based on close but aprox distances".

I would definately go to the 12" standing height 700lb'ers and be willing to trim to fit if needed for ride height rather than getting the 11's and being too short- my guess is they will compress at least if not more than 1 1/2" and leave you too low.

Again its a crap shoot, so best to err on the taller side and trim to fit. Trimming will only increase rate aprox 10-50 lbs at that rate of spring.

Good luck. (the editor of this post assumes no responsibility )

Edit: my front springs are aprox 800lbs and compress aprox 1 1/2" with the car lowered 2" and are compressed about 10" at ride height-NOTE: I DON'T RUN ISOLATORS THOUGH.

 

Why not something like the Ground Control weight jacker kit? A variety of spring rates plus pretty much an unlimited choice in ride height (unless you slizzam it r!cer style ).

Pat

 

Thanks v6toy, I am going to read this when I am more awake. But your figures make more sense then what I was coming up with.

slow350. Reason I dont want Ground Control weight jacker kit is because the class I want to run in, added weight, labor/hacking to install, cost of install, cost of kit (I'm on tight budget), daily driver, and I never plan to change my ride height after its in. But thanks for the suggestion, if it was strickly autocross and had a more forgiving budget, I would look into it.