Throughaxles

Through-axles are a type of bicycle axle that passes completely through the frame and hub, securing the wheel with threaded ends on both sides. They replaced traditional quick-release skewers on many modern bikes, especially those with disc brakes, to improve wheel stiffness, alignment, and brake performance. The through-axle system clamping force is typically distributed across the frame’s dropout and the hub end caps, giving a more precise and rigid connection than a skewer.

Design and variations

Through-axles are hollow cylinders that thread into dropout ends or end caps. The wheel is inserted and the axle is screwed in from each side, tightening the hub to the frame. Some designs use opposite threading on the non-drive side to help prevent loosening during riding, though thread directions and pitches vary by manufacturer. Common diameters are 12 mm and 15 mm, with widths defined by hub spacing.

Common standards

Front through-axle standards include 12x100 mm and 12x110 mm (Boost). Some frames use 15x100 mm or 15x110 mm designs, depending on the fork and brake mounting. Rear standards most often seen are 12x142 mm (non-Boost) and 12x148 mm (Boost); older frames may use 12x135 mm. Compatibility depends on frame dropout width, hub width, and end-cap design.

Advantages and considerations

Through-axles improve lateral stiffness, wheel alignment, and rotor triangulation for disc brakes, facilitating easier wheel installation and consistent clamping forces. They can add weight and require compatible frames, hubs, and tools. Some frames and hubs offer end-cap options or adapters to convert between through-axle and quick-release setups.

Maintenance and compatibility

Owners should ensure matching frame and hub standards, observe manufacturer torque specifications, and keep threads clean and protected. Conversion kits exist to switch between through-axle and QR in certain cases.