A good rule of thumb is that most cars can be lowered about 1.5 inches without complications. Beyond that, changes in a severely lowered car's suspension may negatively affect ride quality, tire wear and increase the risk of "bottoming."
Increased spring rates are required to control vehicle movement with reduced suspension travel. Eibach and H&R usually provide the required higher spring rates using progressive rate springs that minimize the effect on ride quality. However, the lower you go the higher the spring rate required!
Vehicles must always be realigned when lowered. Severely lowered vehicles often experience difficulty in achieving adequate wheel alignment without the use of aftermarket suspension adjusters.
Reduced suspension travel increases the risk of bottoming. While bump stops help prevent bottoming damage, removing or modifying them should only be done if instructed to do so by the spring manufacturer.
Orders
