Rather than use the wider is better design that seems to be all the rage, Shimano put the Dura Ace 9000 C24 Carbon Road Wheelset to wind tunnel testing. The result: the 21mm front and 23mm rear rim depths, coupled with a rim width of a narrow 20. 8mm were found to not only create a smoother airflow, they also increased stability in a crosswind. Additionally, compared with its closest relation, the C24 WH 7900, the C24 WH 9000 features greater rigidity and vertical compliance for a comfortable ride. While the wheels are a high modulus carbon fiber, the braking track is aluminum for reliability. A lightweight, aerodynamic wheel is useless if it doesn't accelerate quickly. For this reason, Shimano ensured that the bulk of the rims' weight is at the center. Shimano used a specifically designed bearing that is able to be pushed to the outside of the hub. The hubs also feature wide flanges for torsional and lateral rigidity, A7075 alloy axles, and a titanium freehub body. Sixteen radial laced spokes are used on the front wheel and 20 double cross on the rear.