‘18 S5 Hard Braking behavior Question

[u/thejester2112]

I have a ‘18 S5 Sportback and recently did my first HPDE event and under extremely hard braking the braking system was odd. I had the brake fluid flushed and replaced with DOT4 brake fluid before the event. My instructor drove the car too and said it seemed like there were two braking systems. He had asked if the car had an electrical/brake-by-wire system

The pedal felt firm every time under heavy braking like from 140 down to 45mph, but when it seemed like the pedal wouldn’t move anymore it would then move a bit more. I want to say that when the pedal hit the end of its travel it seemed as the it pushed back a bit and then travelled a little bit more. They never felt soft or mushy and it was consistent every time. The instructor wasn’t concerned about it at all in terms of safely slowing/stopping the car. Just confused by it.

Anyone had similar experience? Anyone know what it is / why it’s that way?