Identifying the crank spindle.
You can do this by:
• Checking the brand and model printed on the crank
• Looking up the crankset’s specifications
• Measuring the spindle with a vernier caliper
• Checking whether the spindle changes diameter from one side to the other
Do not assume every crank from the same brand uses the same spindle. SRAM, for example, has produced GXP, DUB and 30 mm crank systems.
Common Crank Spindle Standards
Shimano
Modern Shimano road and mountain bike cranksets generally use a straight 24 mm spindle.
This includes many cranksets based on Shimano’s Hollowtech II system.
SRAM GXP
SRAM GXP cranksets use a stepped spindle:
• 24 mm on the drive side
• 22 mm on the non-drive side
The reduction to 22 mm is a defining feature of GXP. A conventional straight 24 mm bottom bracket is not automatically compatible.
SRAM DUB
SRAM DUB cranksets use a spindle with a nominal diameter of approximately 29 mm.
DUB was designed to work across a wide selection of frame standards, but each frame still requires the correct DUB-compatible bottom bracket.
Modern 30 mm Cranksets
Many contemporary 30 mm cranksets use a longer spindle designed to work across wider frame shells.
Examples may include:
• Rotor 30 mm systems
• FSA 386-style cranksets
• Race Face 30 mm cranksets
Although these cranksets share a 30 mm spindle diameter, spindle length and frame compatibility still need to be checked.