To determine your spring rates, Remove springs from your struts then set the car at the desired ride height using a trolley jack. Lower the car and check the amount of available travel before fouling occurs or end of travel is reached. Write down the bump travel. Raise the car fully till the arms are at full droop and measure the total suspension travel.
Belgian Roadster The front corner weights on your car should be approx 250 kgs (550 lbs). Designing the suspension for a maximum load of 2.5G's for club/road use The maximum load is 550 *2.5=1375 lbs.
Divide this maximum load by the amount of travel available and you get the rate in lbs/inch that will provide the load on the springs to fully limit travel with 2.5 G's.
If your car has 4" travel then 1375/4" = 345 lb/inch springs.
For 6" travel 1375/6" = 229 lb/inch springs.
This gives the spring rate to use.
The length of the spring to use depends on the position of the spring platform and is a secondary consideration after the necessary rate has been determined. The spring must remain captive on both platforms at full droop. This can be adjusted by limiting droop travel or fitting tender springs if only short springs are available in the required rate.
If using premium quality shocks the valving rates are determined by the spring rate and the corner weight and usually do not require further adjustment for normal use. On race cars the adjustemt is needed to take account of varying race conditions such as wet tracks.
For other brands that have double adjustable functions you must select a shock that has a suitable range of adjustment in both the bump and rebound for that application. Often adjustables ( and some double adjustables) sold over the counter are not suitable for the application. At best some single adjustables have pathetic low, intermediate or high shaft velocity valving and are not much more than jazzed up tap valves. In shocks you usually get what you pay for.
The shock stroke should exceed the total suspension travel. Droop can be limited by fitting internal bump stops in the shocks if required.
My 2 cents worth
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