Crank arms
Crank arms sold without a chainring, to build your own crankset: carbon or aluminium, SRAM DUB or Shimano 24 mm spindle. Choose the length first, then what goes on the front, chainring or power meter.
Length sets your position
Crank length is as much a position adjustment as a choice of equipment. The Cybrei GP-3 crank arms come in eleven lengths, from 150 to 175 mm in 2.5 mm steps. Going from 172.5 to 165 mm puts the foot 7.5 mm lower at top dead centre: the hip opens, and the knee comes up less. Leverage drops by about 4%, which you get back by spinning at 94 rpm instead of 90.
The interface decides what goes on the front
The Cybrei crank arms use the Easton Cinch interface: they take a 110 × 4 spider for a double chainring, a direct mount chainring or a power meter spider. The Stone DUB 8-bolt crank arms take 8-bolt chainrings, spiders and power meters, never 3-bolt ones. Chainrings are then chosen to match that interface.
The spindle: DUB, 24 mm or carbon
The spindle follows the frame's bottom bracket. The Cybrei Ultra make the spindle itself in carbon, about 270 g a pair including the spindle, in DUB only. The choice has its logic: for the same wall thickness, a tube's resistance to torsion is proportional to the cube of its diameter, nearly 1.8 times more at 29 mm than at 24 mm. That large diameter leaves the carbon some margin.
Measuring your power
A spider power meter replaces the stock spider and keeps your chainrings. The Xcadey XPOWER-S GEN2 in its Easton 110BCD-4S version fits the GP-3 and the Ultra, accurate to ±1%, or ±3 W at 300 W. To remove a Cybrei crank, have the ISIS 20 crank removal tool to hand.
Frequently asked questions
Which crank length should I choose?
It depends on leg length and hip mobility more than on frame size. If your hip closes up or your knee comes up too high at the top of the pedal stroke, a crank 5 to 7.5 mm shorter is worth trying; then raise the saddle by the same amount.
Carbon or aluminium crank arms?
Carbon saves weight: about 270 g for the Cybrei Ultra pair with its spindle. Stone's machined aluminium weighs more, but it also passes fatigue testing at 1,800 N. Choose either one first by spindle and interface.
Can you add a power meter to your cranks?
Yes, with a spider power meter, which takes the place of the original spider between the crank and the chainrings. The Xcadey XPOWER-S GEN2 comes in nine versions: take the one that matches your crank's mounting, Easton, SRAM 3-bolt or 8-bolt, or Shimano MTB.