The Benefits of a Carbon Fiber Tire

Brian: I've heard of people getting a tire that actually adds resistance so that you're going slower while pushing higher watts. Why do pro Xterra racers prefer hydrating with bottles mounted in their bike frames instead of using a hydration vest or a camelback with bottles? It seems like you would need to be strategic about timing when you take a drink and as with the camelback, you remove the variable from the equation.