Thus, if the maximum wheel load is 800 kg, the maximum wheel rate is 20 kg/mm, or approximately 200 N/mm. It works out, assuming linearity, that the travel between the maximum load and 1.4 times the maximum load is 16mm. In reality, the load/deflection curve is highly progressive as it approaches the end of its travel, so the actual travel is greater.
Many times, european car staffers have driven cars fitted with coilovers, some H&R coilovers, that were lowered too far, with the spring perches simply screwed down to the bottom of the threads on the body. Discussions with some other technicians suggested the dampers were damaged from frequent bottoming out, but Walter Wirtz said this was not the case. Proper bump stop design in any suspension will prevent damper damage due to bottoming. Over-lowered coilover cars ride and handle poorly, behaving as if badly underdamped, because they are riding on the bump stop. He gave one counterexample of an underengineered Fiat economy car, in which the factory damper bottomed out internally before the bump stop limited travel.
In an H&R coilover system, the dampers cannot control the highly progressive rate that results when the bump stop is used as the working spring. The bump stop H&R uses inside its coilovers has a free length of 70mm and compresses to a minimum length of 28mm when constrained by the damper housing and shaft. That leaves 42mm of compression until the damper effectively goes solid, the first 15mm of which are not stiff. Basically, there is only about an inch between starting to increase the spring rate and going solid. The results are a feeling of the suspension being underdamped and frequent bottoming if the coilover is set too low.
On the other end of the spectrum, maximum ride height with coilovers is constrained by the requirement of limiting travel with the bump stop before coil bind occurs. (Coil bind is the point of full compression at which the spring's coils run into each other, making the spring effectively a solid block of metal.) Threads are usually present on the damper body beyond the allowable adjustment range, allowing the same damper tube part number to be used for a variety of purposes, such as racing. TV documents state the maximum and minimum allowable height adjustment, measured to a point on the damper body.
Furthermore, TV certification on other items, such as a wheel for example, includes fit contstraints such as maximum lowering. If a car is fitted with coilovers that exceed that lowering, the car will not pass its TV inspection with that wheel. However, the TV documents are in German, for German cars. U.S.-specification cars are often slightly different, so installers should follow the U.S. recommendations for lowering. H&R Springs' U.S. tech lines are there to be helpful and answer even the simplest question.