Technical Coil over spring rate ?

I’ve recently bought this car that’s been together for years now and driven so some much needed maintenance is in order , I’ve done a bunch so far and I’ve read and watched videos on how to figure out spring rates but my question is for anyone using the QA1 rear coil overs what is a good spring rate for the rear of my 46 ford sedan, they are already in there now they don’t ride bad but the shocks are blow and need replacing and I’m debating in changing springs since they seem to sage too much with a load in the car . I haven’t pulled the old ones out yet to look for a part number to see what rate the springs are but anyone with some first hand experience would be much appropriated. Here’s a picture of my car and the type of setup that’s in the back now


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Easy way to get the right springs is to weigh the rear of the car to get an idea of what spring rate to use. Need to subtract the weight of the rear end and tires to be real accurate. I just weighed the whole total rear and got close enough to keep me happy. I went from 250 pound springs to 150 pounders for my QA1s.

 

It's a bit more involved than that ^^^^^ but it is stepping in the right direction.
You need to disconnect the springs [eg; shackles] and weigh the rear end. That way you know the sprung weight.
Then you need to know the motion ratio of the coilover springs [this is the angle they're mounted at]
And most importantly .........the spring load for comfort etc.

eg: a car with 1800lbs rear sprung weight [45o per spring] usually has a spring stiffness of about 90-100 lbs/in. So the suspension will settle 4-1/2" to 5" with the weight on it [less if the coils are preloaded]

Spring load is the shape of the arch in leafs ,or free length in coils .

 

3quarter32 is on the right track about getting the right springs ... but also figure in the angle of the shocks ...theres correction tables available that give the mathmatics for calculating spring rate based on mounting angle...basically the more the angle ( from vertical ) the heavier the spring must be ..
Stan

 

you could also consider switching to parallel leaf spring kit with lowering springs

 

I guess I worded my question all wrong I was wondering if anyone has used this setup on a 41-48 ford or something similar and what what coil spring did you use


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