crankarms

Crankarms are the two arms of a bicycle’s crankset that connect the pedals to the bottom bracket spindle. They transmit the rider’s leg motion into rotational force to turn the chain and drive the bicycle. The drive-side crankarm carries the chainrings, while the non-drive side arm completes the crankset and provides balance.

Crankarms are designed to fit a variety of bottom bracket interfaces and spindle standards. Common older designs use square-taper or three-piece spindles, while newer systems employ splined interfaces such as ISIS or Octalink. Many modern road and mountain cranksets use external-bottom-bracket systems like Hollowtech II or GXP, where the spindle is partly or largely integrated with the crankset. Compatibility between crankarms, bottom brackets, and chainrings is essential for proper alignment, chainline, and spindle support.

Materials range from aluminum alloy, which offers a balance of stiffness and cost, to high-performance carbon fiber for reduced weight and tuned flex. Some crankarms are hollow for weight savings, and many sets feature left and right arms of identical construction with different threading or spline interfaces. Some cranksets include integrated chainrings, while others require separate chainrings mounted to the drive-side arm.

Length is a key specification, typically measured in millimeters from the center of the crank axle to the center of the pedal axle. Common lengths range from about 165 mm to 180 mm, with shorter arms potentially improving knee clearance and cadence, and longer arms offering greater leverage. Proper selection depends on rider height, leg length, pedaling style, and bike geometry.

Maintenance involves inspecting for cracks or wear at the arm–spindle interface, verifying bolt torque, and ensuring clearances. Crankarms are commonly replaced in pairs or as needed when signs of fatigue or damage appear.