Working out how long coil over shock springs should be.
Discussion
Hi guys, I am thinking of buying some replacement front coil over shocks for my TVR 350i, this currently has the cortina type set up with massive diameter springs, Spax do a direct replacement coil over unit (G2011) but have no idea what length the springs shoud be, has anyone got a clue how to work this out? is it as simple as adjusting the spring seat halfway up, open the shock to full length then measure between the spring seat and the top spring retainer?
Any help would be most appreciated.
All the best
Jon
Any help would be most appreciated.
All the best
Jon
Others might have a different approach, but since nobody else has responded, this is how I've always done it:
The normal objective would for the springs to have the minimum possible preload when fitted at the correct ride height.
To achieve this, you need to measure the corner weights and suspension leverages, so that you can work out (from the spring rate) how much the spring will compress under the vehicle's static weight.
You then need to measure the distance between the top retainer and the spring seat in its middle position when the vehicle is sitting at its normal static ride height, add this to the amount the spring will compress under the cars's static weight and you have your 'ideal' spring length.
Of course, you can't normally buy springs measured to the nearest millimetre, so round up to the next available length.
The final check is then to make sure that the free length of the spring that you've calculated will be sufficient that there will still be some small amount of preload (ie. it won't be rattling around free) when the damper is at full extension. With stiffer springs, this isn't always so, in which case I'd tend to go for a longer spring and move the spring seat down, rather than the 'bodge' solution of fitting helper springs.
The normal objective would for the springs to have the minimum possible preload when fitted at the correct ride height.
To achieve this, you need to measure the corner weights and suspension leverages, so that you can work out (from the spring rate) how much the spring will compress under the vehicle's static weight.
You then need to measure the distance between the top retainer and the spring seat in its middle position when the vehicle is sitting at its normal static ride height, add this to the amount the spring will compress under the cars's static weight and you have your 'ideal' spring length.
Of course, you can't normally buy springs measured to the nearest millimetre, so round up to the next available length.
The final check is then to make sure that the free length of the spring that you've calculated will be sufficient that there will still be some small amount of preload (ie. it won't be rattling around free) when the damper is at full extension. With stiffer springs, this isn't always so, in which case I'd tend to go for a longer spring and move the spring seat down, rather than the 'bodge' solution of fitting helper springs.
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