The Rotor 3D crankset has been one of RCUK’s most-wanted components of the year, promising as it does both massive stiffness and minimal weight alongside rugged styling straight from the advanced CNC machinist’s manual.
Well, an example is now installed on the editorial Omega and has covered some 100 miles since installation. It comprises 175mm crankarms fitted with a 110mm BCD Compact spider and has taken the place of a SRAM Rival 2009 model crankset. I fitted the SRAM chainrings and installed Token Tiramic external bottom bracket bearings compatible with Shimano’s Hollowtech II axle standard, which the Rotor crankset matches.
Weight of the 3D cranks with axle and spider is around 5g lighter than the Rival equivalent, which it should be noted also has hollow crankarms. The Rotor arms are triple drilled, hence the 3D name, but have a much more substantial cross-section and overall appearance.
Fitment follows much the same process as that for any Shimano Hollowtech II crankset, since the axle is part of the right-hand crank rather than the left hander as with Rotor’s Agilis design. First, however, the left-hand 3D crank must be separated from the axle, to which it is fitted for packaging.
Even with the end cap removed this can’t be done by simply pulling at the crank. Rotor’s machining is done to such exact tolerances that the crank is effectively an interference fit on the axle when the clamp bolt is slack. The trick is to undo said bolt by just enough to spread the ‘ears’ of the crank so it can be slid off.
This works because the crank is fitted with a large example of Rotor’s Dual Thread Technology screw system, which employs two thread pitches on the same screw. One is coarse and one fine so they travel along the thread axis at differing rates as the screw is turned. This provides an exceptionally secure tightening effect but also means that, in this case, the screw pushes the ears apart when undone. Taken far enough this would damage the material of the crank, so the screw may be undone a maximum of 1.5 turns out from tightened. Obviously it cannot be removed completely by the owner.
Once the crank has been removed, the remainder of the process is straightforward up to the point where the end cap is lightly tightened prior to clamping the crank. A torque setting of 1Nm is advised, which in practice means very little. There in an O ring between each crank and its bearing and the torque is just enough to compress these lightly. Only once the crank is tightened onto the axle – to a low 7 – 8 Nm thanks to the DTT thread – may the end cap in turn be nipped up for security.
As with any Rotor component, the unconventional thinking and advanced engineering involved mean that strict adherence to the instruction leaflet is vital. The ‘tread’ or ‘Q’ factor – the width of the pedal centres – is about 1mm narrower than with the Rival cranks, which may be down to the width of the Token bearings. The front mech needed minimal adjustment to work with the new chainline.
So, to the ride. Unsurprisingly, given that the mighty Thor Hushovd rode them to win the 2009 Tour de France green jersey, the cranks are tree-trunk stiff. Tread on the pedals out of the saddle and transmission response is as instant as the frame’s rear end will allow. That of the Omega is somewhat noodly. Indeed, now that the 3D cranks are in place, the whole bike feels comparatively flexy where it chimed nicely with the Rival pair.
In fact, the immediate impression is not merely of stiffness but of precision. So little deflection is evident that there is a crispness to the pedals lacking with any other cranks I have ridden. That this is so is hardly surprising given the sturdy exterior dimensions of the crank arms, which fit with best practice for torque transmission by being of constant section along their length. Torque, or twisting, is the main mode of deflection for a crank arm and these don’t deflect very much.
So, initial riding and spannering impressions are highly favorable and, with a choice of 170m, 172.5mm and 175mm arm lengths and with standard 130mm BCD or compact 110mm BCD spider options, the 3D crankset offers considerable versatility.
Rotor 3D Road crankset £245.00 (cranks, axle, spider)
