Close Call on a Wet Mountain Pass

Was driving my RWD coupe down a twisty mountain road after some rain, pushing it a bit in the corners. Came into a left-hander a little too hot, felt the rear start to step out. Instinctively caught it with a quick countersteer and a light throttle lift heart was pounding! What’s your closest save, and how do you stay calm when the car gets loose? Any tips for handling those unexpected slides?