Timo, don't want to make light of something that can be a safety issue, but this is one of those things that you just have to deal with in IT unfortunately (or fortunately). If the car can't be lowered past a certain point without risk of failure, then that is a performance limitation (in order to avoid a safety one).

For example, on my side, I have to do a number of things to minimize my brake problems. I have to use a less aggressive pad (with corresponding less stopping power) to minimize heat. I'm going to have to run 15" wheels to get better cooling, even though 13"s are better for gearing at most tracks. I have to run SRF fluid, even though it is expensive. And, I have to manage the brakes during a race. I get 3-4 laps of hard stopping power (hopefully enough to open up a decent gap to the next car) before I have to take it easy on the brakes.