Originally Posted by Ant Man
Which M3 springs are you refering to? Eibachs lower the front by 20mm and therefore double the drop of the Edition models.
The purpose of the springs is to hold the car up at the required ride height, allow sufficient movement above and below this point, resisting excessive body roll and allow the wheels to follow the road surface. Spring travel is thus a very important part and the if there is not enough travel, the spring bottoms out. Effectively that corner of the car ceases to have suspension.
If this happened when cornering or braking hard it could be very dangerous.
The M3 front suspension has 0.5" of travel before hitting the bump stop. The bump stop has been dyno'd and acts progressively over the first 1" of compression. It's resistance then shoots up at which point it is not acting like a spring.
The front M3 springs are rated at 160lbs, meaning it takes 160lbs of force to compress the spring by one inch. With two adults in the car you are already eating into the available spring travel.
So with the Eibachs you are already riding on the bump stops, yes the springs are stiffer by ~22% but only at the maximum compression (as they are progressive) and this will potentially create a worse handling car.
Below are the threads to read
+1, there's simply no escaping that the car's dampers will wear out faster with aftermarket springs of any kind. Eibachs being the least intrusive of the bunch due to its more conservative drop.
Also, keep in mind the car's dynamics change slightly with springs that inherently "rake" the car forward to compensate for the front fender gap. This could be avoided with a sleeve kit from KW or GC.