I rode from SF to the Mt Tam eastern peak viewpoint and back yesterday, 56mi 5000 ft in 4.5 hours including stops. Temps were in the low-mid 70s and I drank three 28oz bottles with highly dilute cytomax. If temps were in the mid-high 80s I would have gone through a fourth bottle in the same ride, ridden slower, and used less dilute cytomax. I use a Profile Designs Aqua Rack. While I typically carry a backpack with clothes, food, a spare tire, lights, etc on a ride like this, I like to put heavy items like water bottles on the frame rather than on my back.