Since installing the 1.20 update (v1.20.155766), when ever you depress the brake (l-trigger) the engine revs (RPM) drop to idle & the wheel spin / traction loss icon/alert appears.

Hitting the accelerator (r-trigger), brings the revs (RPM) back up to normal.

Additionally, if you red line the revs the engine now makes a weird gear grinding sound (which sounds nothing like an over revved engine) - maybe this was intentional?