Monoposto Racing Forum

I got a box full of coil springs assorted, but have had the markings removed, so not sure what their ratings are. Anyone got a spring tester that can test the rates for me?

You should be able to work it out close enough with a tape measure and a set of bathroom scales.

You can calculate the rate with a fair degree of accuracy (at least it'll tell you the nominal rate).

You need the wire diameter (without the powder coating if possible), the outer diameter of the spring, the free length of the spring, and the number of ACTIVE coils*. We can probably assume they are all a fairly standard spring steel, so 'normal' values for Young's Modulus etc can be used.

* the number of active coils is the number of coils that are not coil bound. Often the ends of springs are wound at a tighter pitch and then ground off, so it's usual for between 1.5 and 3 coils to be less than 100% effective compared to the main working area.


If not, then I'm sure someone will have a spring tester. A damper specialist will probably have one, and I've used Shaun Pickering quite happily over the years - 07811 108123

Andrew - if these are typical Formula Renault springs, then rates of around 900lb/in are likely. So a person standing on it would only compress it about 5mm at the most, and it's quite hard to measure whilsting standing on it!!!

I made a test rig using the bathroom scales and a lever (only for 4/500lb springs), it sort of worked but lets just say that set of scales was no longer required in the bathroom after that!

Note - working out wheel rates, spring rates, roll stiffness and the like using Mr Staniforth's maths doesn't work properly for monoshock cars, as they behave rather differently.

Got it all sorted... thanks for the tips.