Originally Posted by
MONGO!
The main advantage is weight. Carbon is light, so you can make the rim deeper and more aerodynamic while keeping weight down.
This is basically the answer. The thing that makes "Carbon" wheels fast is NOT the carbon but the fact they have deep sections of 40mm or even 60mm. This makes them more aerodynamic but a wheel rim this deep in aluminium would be very heavy. Now while these very deep carbon rims still aren't that light they are lighter than if they were made with aluminium so they are a much better proposition for an all round wheel.
Anthony