Kyle Busch says other drivers "piss themselves" all the time during races ... but despite his best efforts, he can't join NASCAR's #1 club.
We got Kyle and his smokin' hot wife, Samantha, out at Craig's ... and the conversation quickly turned to racing's dirty little secret -- peeing in the cockpit!
Busch told TMZ Sports he's "tried like hell" to pull the trigger -- races are 3 HOURS long -- but he can't bring himself to go full R. Kelly on the track.
But KB says some guys got no problem taking a leak mid-race ... and even claims one of his teammates broke the seal BEFORE his race started!
Yeah ... Samantha's face says it all.