Originally Posted by Fat Boy

Noakes basic hydration premise is 'drink to thirst'. Now I think on a bike there is a cooling issue that runners don't deal with, which is that the increased air speed makes for more effective cooling due to perspiration evaporation. A cooler rider is probably going to be a faster one. Also because of the higher evaporation rate, maybe we can get excessively dehydrated more easily. In either case, it seems to make sense to just spray water on yourself rather than drink it to facilitate sweating.

Noakes doesn't worry about dehydration. He says that if you get 'too' dehydrated, you'll just slow down (no big deal to him - a marathon runner). For a bike racer, if you slow down, your day is done. He does note that the faster marathon runners are the ones that are the most dehydrated at the finish. I think this may have something to do with the lack of slowing in feed zones, but it also has something to do with the fact that the fastest runners will have the highest sweat rates (due to greater energy output).

I used to drink a lot on the bike (much more than thirst). I never got myself into a problem with drinking too much, but after a ride/race I might spend the rest of the day hitting the head while my body shed all the water I'd drank. After reading Noakes' thoughts, I drink less. I don't restrict fluids, but just drink to thirst. If it's hot, I drink more, if it's cool I drink less. I have yet to find any real down side on the performance end.