The depth of these full-carbon C40 wheels makes them an ideal choice for a rider who needs a lightweight and stiff wheelset for repeated sharp attacks on steep cols and bergs as well as nabbing a sprint in a small select group at the end of a 5-hour slugfest. Its depth offers increased lateral rigidity and gives it enough aero benefit to help that attack stick if that's 30k from the line or a late-race surprise inside the flame rouge. Shimano offers a deeper wheel at 60mm for even more aero benefit, but for most riders, we feel this wheelset, at 37mm deep, add enough of an aero benefit without losing stability in windy conditions.

Shimano engineers considered both frontal and crosswind forces when developing the rim's profile. Through prototype testing, both in the wind tunnel and on the road yielded a wide rim shape with a deep tire bed as the best performer across a wider range of conditions. This shape, known as D2, reduced drag better than previous versions and competitor's profiles at yaw angles ranging from 0 to 15-degrees. An added bonus of the rim's profile is its improved vertical compliance for increased control and comfort over rougher roads. Helping bolster the aero benefits, even more, Shimano uses bladed spokes and places the spoke nipples internally which makes truing the wheels a little more tricky, but given these wheels' track record on the WorldTour circuit, we don't see ourselves having to do that very often, if at all.