BASICS
Before we look at how and why we set up a suspension system, let’s remind ourselves of the absolute fundamentals. We need suspension to cushion out bumps and to prevent wheels leaving the ground every time the vehicle hits a bump or dip in the road. If suspension settings are too stiff neither of these requirements are satisfied (most of us have seen Fl cars balancing on three wheels when they get a puncture - their suspension is very stiff), whilst if the settings are too soft we need a lot of suspension movement (and corresponding ground clearance) to stop the axles bottoming out on their bump stops. Body roll also becomes a problem.
Ignoring the intricacies of geometry for the moment, what the suspension sees when it hits a bump is a vertical acceleration directly proportional to the size of the bump and the speed at which the car hits it (large bump at high speed = large acceleration). The spring’s job is to absorb that acceleration by turning it into potential energy. It does this by compressing, then as the acceleration is reduced or removed it extends back to its normal length and thereby releases that stored energy by restoring the vehicle to its normal ride height. The shock absorber’s job is to slow the whole process and stop the car oscillating up and down.

COMPROMISES
Our suspension must therefore compromise between:
1. too soft or too hard.
2. Not enough or too much roll resistance.
3. Overall suspension characteristics.
Our Fl car analogy can he further extended by comparing it with a mid-’60s American sponge wagon. Both represent no-compromise approaches to two opposed requirements. The job of the suspension on the Fl car is to make the car corner as quickly as possible and at the same time restrict the change in height between the underside of the car and the road surface for optimum ground effect. Because suspension travel is restricted so much the spring rates are extremely high in order to prevent bottoming out as much as possible. Why does this matter if driver comfort is of no consequence?
Simple, every action has an equal and opposite reaction. If the suspension hits the stops hard the car will leap off the ground and if that bump happens to be on a corner, the next time the wheels contact terra firma the car might already be in the scenery. The uncomfortable ride that results from the above is in direct contrast to the Chevy cruising down to the local burger bar. Its marshmallow suspension settings can be viewed as follows:
1. Plenty of travel to absorb large bumps without transferring energy through to the passengers.
2. Soft springs allowable because of large amount of travel.
3. Plenty of ground clearance to give full rein to the suspension.
4. Soft acting shock absorbers to prevent artificially hardening up the springs.
5. The anti-roll bars must be equally soft to prevent the independent suspension units tying together too much, hence -
6. Body roll when cornering.
7. Pitching occurs over transverse ridges or when coming to a sudden stop.
We don’t need to use our imagination very much to realise that the suspension settings in the two cars give one that corners on rails but is damned uncomfortable and one that glides along is if it were airborne but responds badly to changes in direction

.

To support the weight of the car the spring must compress:

750x2 3.75”
400

We have therefore exceeded the safe stress of the spring before the car has even started to roll.
The accepted remedy as our over stressed spring begins to settle (permanently compress) is to fit ever stiffer springs. This is all very well if you want stiff suspension with minimum travel but if you don’t, what next?