Cranksets & Crank Arms

Selecting a crankset starts with the drivetrain architecture. Crank arms need to match the relevant spindle or drive interface, geometry and drivetrain requirements to ensure stable load transfer and alignment.

Key parameters include:

• Crank arm length and geometry 
• Spindle interface type and fit
• Spindle diameter
• Required spindle length and chain line 
• Q-factor and ergonomics 
• Compatibility with bottom bracket housing standards
• Gear ratio
• Target application, including city, trekking, mountain and road bikes

For square taper systems, cranksets and bottom brackets are specified together to ensure drivetrain alignment and predictable assembly.

AVAX A and AVAX S use a square taper interface and are designed for use with compatible THUN square taper bottom brackets. Matching spindle geometry, interface fit and tolerances helps maintain secure load transfer and drivetrain alignment.

Depending on the bicycle platform and configuration, relevant THUN bottom bracket families include GOAL, PASO and TWIST, IBEX, JIVE and TANGO, and ZUMBA.

• VANGUARD is designed for e-bikes with mid-drive systems. It follows a different system architecture and is not paired with a THUN bottom bracket.

For square taper cranksets, performance depends on precise alignment between the crank arms, bottom bracket spindle and frame.

The crank arms must engage securely with the spindle. Correct spindle length and chainline help maintain drivetrain alignment, while a consistent Q-factor supports predictable fit and rider ergonomics.

Relevant parameters include:

• Spindle length and chainline 
• Interface fit between crank arm and spindle 
• Q-factor consistency 
• Frame alignment and clearance 

Incorrect alignment leads to noise, reduced efficiency and premature wear at the interface.

In series production, drivetrain reliability depends on interface stability across the crankset, bottom bracket and frame. Tolerance variations at these interfaces cause micro-movement, noise and premature wear under load.

For square taper systems, stable crankset performance requires secure spindle engagement, controlled tightening torque and a consistent Q-factor. Together, these reduce movement at the crank arm–spindle interface and ensure long-term durability.

For compatible bottom bracket systems, THUN controls spindle geometry, interface tolerances and assembly specifications. This reduces variability and keeps quality consistent at scale. The result is predictable installation, whether assembly is automated or manual.

A crankset does more than transmit force. Its geometry, spindle interface and alignment determine how cleanly it integrates with the frame and how the drivetrain behaves under load.

Crank arm length and Q-factor define rider ergonomics. Chainline and spindle position determine drivetrain alignment and efficiency. Crankset dimensions affect frame clearance and structural behavior, particularly under dynamic pedaling loads.

When the fit between crank arm and spindle degrades, micro-movement follows. This accelerates wear, reduces efficiency and shortens service life.

Tight, consistent tolerances help keep the crank arm–spindle interface stable across repeated load cycles. A secure, well-matched interface reduces micro-movement, supports long-term durability and helps limit maintenance requirements in real-world applications.