Most race car drivers do not wear diapers while racing because most race car drivers take salt tablets which prevent dehydration and so they don't need to drink more liquids to make them need to urinate as often.
The heat also causes the race car drivers to sweat enough that they don't need to urinate as much and can usually wait until the race is over to use the restroom.
There is an exception though as I have a friend that's a race car driver and he does wear diapers but not because of racing per say he wears the diapers because deals with slight incontinence and leaks urine so he wears the diapers to keep his pants dry.
He doesn't wear the diapers all the time during the day because most times he can make it to the toilet in time but not when he's in a race car or just driving around in general.
So some other race car drivers may wear diapers while racing if they're incontinent however most race car drivers don't wear diapers during racing.