The shimano dura ace c40 carbon clincher wheel featuring a 35 mm deep carbon rim with alloy braking track the depth of the rim adds aerodynamic properties to the wheelset making riders faster over the line whilst the alloy braking track allows assured braking in all conditions the c40 combines this with a 20 mm rim width allowing riders to choose wider tyres using a wider tyre 25c creates a greater contact patch with the ground and allows for a more linear bond between tyre and rim giv