I would disagree with sailor. I have had a carbon bike and recently moved to an all aluminum bicycle. The all aluminum bicycle was lighter than the carbon. Same size bicycle. Aluminum is a comfortable ride especially if you have a carbon post, stem and handlebar. Also if you want maximum output with pedaling go aluminum. At my LBS a science major did the stiffness of carbon and aluminum. You lose power when you pedal with aluminum because that's exactly what it does... It takes up vibration so it naturally takes up your power. I say aluminum but ride both. My 2 cents.