Well known for their elliptical Q-Ring chainrings, Rotor also make a range of lightweight cranks to match. The 3D cranks have been designed with input from the Cervélo TestTeam, including sprinter Thor Hushovd, and feature triple-hollowed aluminium arms.
To create the hollowed structure, Rotor have bored out three holes along the length of the crank, using CNC machining, before machining the external surfaces to further reduce weight, a method they call the ‘Trinity Drilling System’.
A replaceable and heavily machined chainring spider (available in compact or standard chainring sizes) is attached to the driveside crank, and the 24mm axle is compatible with Shimano’s external bottom brackets as well as Rotor’s own SABB (self aligning) unit.
Out on the road power transfer was very good, but we did ﬁnd our chainrings – Ultegra and Rotor Q-Rings – ﬂexed more than with other race inspired cranks when the chainline wasn’t perfectly straight. Our testing showed the chainring spider was to blame, and for the slightly delayed shifting that came with it.
For riders whose usual routes involve frequent shifting between rings, the delayed response may begin to grate after a while, but in all other respects the 3Ds performed very well.
Fitting was very easy, with the unique Dual Thread Technology (DTT) ﬁxing bolt clamping the non-driveside crank to the axle by using two different pitched threads on a single bolt.
It’s important to follow Rotor’s instructions as the DTT bolt works in a slightly different way from standard ﬁxing bolts, but the upshot of this small change in procedure is that the clamp area is less heavily stressed by clamping and so can be more heavily machined for reduced weight.
We tested the titanium-axled version which weighs 497g, placing it squarely in the lightweight class. The precisely etched graphics and black and red colour scheme look great too.
For £150 less you can buy the steel axled version which adds just 34g to the total weight. Good power transfer and light weight are both positives but we’d like to see Rotor stiffen the chainring spider to make these real winners.