By John Stevenson and James Huang
Component manufacturer Shimano has officially announced details of the crank and front derailleur for its new XTR mountain bike group. Some details of the new parts leaked earlier this year, but the announcement reveals new information including a change in the attachment of the left hand crank to the axle.
The cranks has several significant new features. To save weight, the pinch bolts that held the left hand crank in place in the previous Hollowtech II design are gone. According to Shimano's Devin Walton the change is intended to "create a lighter interface without all of the extra metal that was designed just to handle the stresses of the opposing pinch bolts, let alone the pedaling forces."
However, one advantage of the old design was that it allowed bearing pre-load to be set by lightly tightening the preload nut in the end of the crank, in a similar manner to the way the bearing in a threadless headset is adjusted. The new design separates crank attachment and bearing preload.
"Once the crank arm is fixed to the spindle with the end bolt, the adjustable lockring behind the arm adjusts out the play and actually provides for more precise bearing adjustment than the threadless headset-like set up," Devin told Cyclingnews when we asked for clarification of the new design.
According to Biketesting.com, a third-party test lab, eliminating the pinch bolt setup should also increase the rigidity of the non-drive crankarm relative to Shimano's existing setup.
Read the entire article over in the Tech News section.