Did another experiment today on a 2.5 hour ride. Again I was just focused on water loss (not electrolytes - a different question). And I DON'T CARE how much water bottles weigh, BTW (not at all the point).

Me loaded up (including two full 22 oz. water bottles, shoes, helmet, clothes, etc) was 165.2 pounds. Me after the ride with all the same stuff (except one water bottle was empty) was 154.3 pounds. So 4 pounds/hour water loss rate (high 80's, not humid by south eastern US standards) is a decent planning assumption here it would seem.

So assume the following.

• 5.5 hour century -> 22 pounds of water
• Pre-hydrate 2 pounds (really don't know what is reasonable here)
• Consume a 22 oz water bottle every 45 minutes (for 5 hours - the water taken in the last 30 minutes will really only help recovery). This is at the edge of how much water your body can absorb during exercise, from what I understand.

The above seems to me to be reasonable (validity of the assumptions plus do-ability of the hydration, assuming some pretty good support on the route). And this yields a net loss of around 10.5 pounds which is a little under 7% body weight and this is a total NET water loss in the range of what I have tolerated in the past, including today. I could consume more water, but I'm not sure that I could absorb it (from what I know).

So I guess that this can be done, but I will have to train myself to consume this much fluid. I haven't done anything in a while over 3 hours and even those rides have typically ended at dusk with lower temps.

Electrolytes - a different question and it is my experience that the content of your sweat changes dramatically with heat training.

FWIW.

dave