at the hottest races they can lose up to 10 lbs. in nascar. i can remember kyle busch having salt on his firesuit from evaporated sweat a year or two back. but on average they lose about 3-6lbs.
idk about f1 though my guess is that it would not be as bad because of the fresh air moving around due to the open cockpit
I'm not certain on Formula 1, but I've heard it isn't anything for a NASCAR driver to lose at least 10 lbs in a single race. They sweat like crazy in those fire suits that's why it's so important for them to stay well hydrated and cool.
