The recreational cyclist could certainly get away with riding one bicycle both up and down hills, but that wouldn't satisfy the bike addict's needs. Downhill bikes are designed specifically with frame stiffness, brakes, suspension, and weight in mind. A downhill bike is meant to increase the handling and speed potential. The amount of hardware required to accomplish that makes the bike extremely heavy in comparison with a cross-country bike, which needs to be efficient. The average weight of a cross-country bike is 25 pounds. A downhill bike can weigh up to 45 pounds. In theory, you could ride it uphill. Unless the neighborhood pit bull was chasing you, would you really want to?

--Cyrus Krohn