Carbon rim query

What’s the advantage over aluminium? Do they last longer? Do they not crack at the spoke holes like aluminium ones do? Are the dimensions as good as aluminium rims?

MikeDee, via the Cycling UK Forum

Where bicycle wheel rims are concerned, the advantage of carbon fibre over aluminium lies in the former’s much greater stiffness for its weight. This makes it possible to build deep-section aerodynamic rims without the significant weight penalty of an aluminium rim with the same aerodynamic profile. The answers to your other questions depend on the manufacturer but, in general, carbon fibre rims are durable and manufactured to the same dimensional standards as their aluminium equivalents.

However, carbon fibre rims provide a less effective braking surface than aluminium and generally require blocks with a carbon-specific compound, if used with rim brakes. Heat can build up in the material on long, twisty descents and lead to tyre blow-off. Problems with braking on carbon-fibre rims are arguably the primary driver for the promotion of disc brakes on performance road bikes.

Richard Hallett

​​Cycle’s Technical Editor