Original Equipment Manufacturer. Three good words to live by when you’re taking care of your car. Choosing OEM parts mean the replacement parts will live up to the design specifications of the designers and engineers that created the car (barring significant recalls and known defects). And those people have gone through A LOT of rigor to ensure all components of the car comes together and performs well. For instance, take a look at this video of a front suspension test rig.
The rig was used to torture the front suspension of an E39 BMW M5. Judging from the noises, squeals, and massive tire deformation, the test rig was putting the M5 through some serious acceleration and deceleration tests, while being loaded in all sorts of ways. This relatively compact rig allows the engineers to abuse the front suspension design before a prototype hits the streets. Chances are these tests would be run for several hundreds of hours, so they can pick up on any flaws and signs of wear.
So when you’re thinking about modding your suspension with some cheap springs or coilovers, you should wonder whether they’ve put those components to the test. And if you want to slam your car to the ground, you better know what you’re giving up.