Coil Spring Rate calculator

[chiefyo]

http://www.reliablespring.co.uk/calculator.htm
Hello I came across this and found it useful.

[S2Andy]

Out of interest I used the calculator to test my original front springs using the corresponding original fixed seat Koni dampers.
Spring thickness 12.5mm, outside dia 84mm, No of usable coils 13, Free length 282mm, damper length 255mm.(all measured using a digital caliper)
This gives an original spring rate of 300lb/inch which is appreciably less than most people are using now, and a preload of 310 lbs.
I bought some aftermarket 300lb/inch springs which were far too soft and I am using 350lb/inch springs currently.

[chiefyo]

Hello Andy interestingly I found this calculator to do exactly as you have - that is calculate the original spring rate fitted to Konis, and I came out with the same as yourself 300 lb. Yet as you point out when replacing everyone goes above this figure interesting !!!

[Ragtop]

My original springs are variable rate (progressive), ie start soft and get firmer when compressed - aren't yours the same? And if so, how are you calculating the spring rate?

Graham

[S2Andy]

No, my springs are uniformly wound and wire diameter is constant. 1990 car, so perhaps variable rate came later.