It's the biggest question Daytona 500 champ Jimmie Johnson -- and every other NASCAR driver -- faces during a grueling 3-4 hour race ... HOW DO YOU GO TO THE BATHROOM??? And JJ actually gave us an answer.
Jimmie -- who was out in NYC yesterday -- told TMZ, "Some guys just go." Yes, in their pants.
But the 5-time Sprint Cup champ adamantly denied ever wetting himself, adding ... "I never have. Of course I wouldn't do that."
SURE YOU WOULDN'T.