carbon mountain bike rim
Weight
Bonded carbon parts are typically lighter weight than aluminum. Carbon cranksets tend to weigh between 700 and 800 grams (24 to 28 ounces). That is less than two pounds for both crank arms and the full set of chainrings. Aluminum cranksets, however, tend to weigh between 900 and 1000 grams (about two pounds). While the difference between 28 ounces and 35 ounces might not sound like very much, that is a 20% weight difference. Every time you pedal, you will be using 20% more energy. On a long ride or up a steep hill, that difference could quickly become exhausting.
Durability
Where aluminum falls behind bonded carbon in weight, it is the definite winner when it comes to durability.
Aluminum arms tend to be stiffer than carbon fiber because they tend to have a larger construction. Stiffer cranks are often preferable, especially for anyone who wants to sprint. This is because more of your kinetic energy is delivered to the wheels, and less is lost due to the arms flexing. The metal is also more durable because it is one solid construction as opposed to a blend of fibers such as carbon.
