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HighRev ...I hope you do not mind ...I am going to add my thoughts to what you started ...
Suspension Travel
When you lower a car via lowering springs you are doing a number of things
Shorten the suspension travel (As above) … less travel means the suspension has less movement to absorb the changes in the road surface …ie potholes … you are much more likely to bottom out and hit something important (like an oil-pan).
You MUST have higher spring rates to keep the car within the new suspension travel range. Why … Well the OE springs are designed with a specific spring rates and a specific spring compression (travel) Remember that spring rates are a measure of a springs length compressed by the amount of force(weight) … ie 200 lb/in springs will compress 1” for every 200# applied to them.
If the Stock suspension has for example 6” of total travel, and you lower the car by 2” you have reduced the overall travel by 33% to 4”. So what you say, well the weight of the car has not changed … and if the spring rates are similar to stock, the car will NEED the same amount of suspension travel as OE (6”) but you are only giving it 4” (lowering springs) …so now you will be using all the springs travel AND the car suspension will be spending a lot of time on the bump-stops rather then being supported by the Springs. Related to this, when you shorten the travel you also shorten the distance the shock has to damp the oscillations, so it has to work “harder” with an shorter distance and time.
Bump Stops
-Bump stops are springs … when the suspension runs out of travel it compresses to the point where the car is actually running on the bump stops. Since the bump-stops are actually elastomer springs with a high spring rate, your car “suddenly” goes from one spring rates (springs) to a much higher spring rate (bump-stops) causing the handling to become inconsistent and difficult to control. You car can and will suddenly go from under-steer to over-steer (or vis-versa) mid-corner as you load the suspension up and compresses the springs to the point where you are sitting on the bump-stops. Related to this, you shocks valveing are designed (hopefully) to properly damp or control the oscillations of the springs (based on the spring rate) … when you are running on the much higher rate bump-stops the shock have NO chance in damping them, adding to the instability of the suspension system at the limit (where you need the most stability)
Changing the frequency of the system
-As you increase the spring rates you also increase the frequency at which the suspension operates … The definition of frequency is “cycles per second”. Low spring rates provide long slow motions, high spring rates provide shorter, faster motions. This increase in speed and frequency obviously increases the “work” the shock has to do to damp the motions of the springs. When the car is riding on the bump-stops, the spring rates go up HUGE, thus the work the shock has to do is substantially increased. The Valving of the shock is not only designed for the specific spring rates but also the frequency that the suspension operates at … the valves and orifices are designed to flow a specific volume of fluid at a specific rate … the high frequency motion is beyond the high-speed damping ability of the shock, and as a result it cannot damp these higher rates and the highly increased flow rates wear out the shock WAY faster than normal.
It is my theory that the average lowering spring wears out shocks because it spends so much time on the (high-rate)bump-stops thus speeding up the wear on the shock.
Bottom line … lowering springs do not work well and actually negatively effect suspension performance for the following reasons
-Decrease suspension travel without compensating (with increased spring rates) for this loss in travel
-Allow the suspension to spend WAY more time then it should on the bump-stops … causing instability and wear
-Run beyond the shocks ability to damp the springs rates and motion frequency, and increase the wear on the shocks.
Any changes to the suspension must be systematic ... you need to create a complementary series of components that work well together.
-Spring rates matched to the ride-height and weight transfer charateristic you require
-Bump-stop travel and rates matched to the above
-Shock valving and travel matched to the above
Moose
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