Shimano

Dura-Ace 9100 C24 Carbon Laminate Road Wheelset - Clincher

When Shimano first released its Dura-Ace carbon laminated clincher, we swore we could hear palpable sighs of relief from cycling forums, group rides, and tech geeks thumbing through the glossies. Some we're sure exercised healthy skepticism, as the first round of carbon clinchers had done a good job at inspiring fear rather than confidence, but as time went on, it became clear that, by combining the lightweight of carbon with the reliability of alloy, Shimano had somehow conjured a wheel that rose above the hindrances its ancestors had faced. The Dura-Ace 9100 C24 Carbon Laminated Clincher Wheelset continues the legacy its landmark predecessor established, updated to modern standards and remaining every bit as strong a member of the carbon clincher category as it was when it was first introduced.

The C24 may be the least changed member of the Dura-Ace 9100 line, with the only change coming in the form of wider flange spacing, which further increases the wheels' torsional and lateral rigidity by improving the spoke bracing angle. The previous C24 hubs were already relatively wide because of Shimano's angular contact bearings. The bearings' shape allows them to be pushed as far outboard as possible, making the hub a wider platform for the spokes to stand on and making the additional width even more impressive. Notably, and despite the increased drive stiffness, the improved spoke angle has no impact on the rim's engineered radial flex, which means the C24 still takes the edge off of harsh bumps.

The rim's construction, which is ultimately responsible for the wheelset's devoted following, remains the same. It involves an alloy body that's extruded and machined to thin the walls down to an almost two-dimensional 0.6mm wall thickness—about half of the typical alloy rim wall thickness of 1 to 1.3mm. This obviously reduces weight to a minimum, but it also does mean the overall structure is less sound, so Shimano buttresses the rim with a jealously guarded carbon laminate process. The only information that the Japanese brand is willing to divulge about this process is that phosphoric acid is used to anodize the alloy, and then variable carbon layers are fused to it in order to boost its structural integrity without undoing the weight gains made during the milling process.

The result is a lightweight rim that's as durable and radially comfortable as alloy but still manages to approach the weight and drive stiffness of carbon. It's also still got an alloy brake track and doesn't sacrifice stopping power in pursuit of weight reduction and also doesn't carry the risk of being distorted by internal pressure from the tube when it heats up during long, hot descents. And though the benefits of safe, confident braking are obvious, the long, hot climbs leading into those descents are where the C24 wheels really shine.

The lightweight rims mean that the wheel's mass is centered at the, well, center, not the circumference, so the amount of inertial resistance you'll be fighting with each revolution of the rim is decreased. Shimano calls this construction philosophy the Accelerating Speed Concept; we call it a wheelset spins up faster and requires less engine power to pin it and hold it. It also means that, on those long climbs mentioned above where inertial resistance doesn't give way to momentum after you've spun them up, each wheel rotation also requires less engine power. Less power means less fatigue means easier climbing.

The front and rear rims' asymmetrical depths continue to play to each other's positioning strengths: the 21mm front is slightly more stable as it combats greater exposure to crosswinds; the 23mm rear is slightly more aerodynamic because it's in a more sheltered position—though of course neither rim can match the aerodynamic benefits of a mid-depth carbon rim. That's also not the C24's job, and those same carbon rims can only dream of the comfort and confident braking enjoyed by the lower profile alloy rims.

Shimano once again incorporates 16 radial-laced spokes on the front wheel, and 20 two-cross spokes in the rear. The spoke holes in the rim are offset, which is meant to accommodate for and counter the asymmetric force of the drivetrain. For further efficiency, the C24 wheelset uses ultra-stiff, oversized A7075 alloy axles, and a lightweight titanium freehub body.