Mountain bike thru axles typically come in a few common sizes, primarily 15mm for the front and 12mm for the rear, though 20mm is also used for specific applications.
Mountain bike thru axles are essential components that secure the wheels to the frame and fork, offering increased stiffness and strength compared to traditional quick-release skewers. The size of the thru axle refers to its diameter. Different diameters are used for front and rear wheels, as well as for different riding disciplines, to optimize performance and durability.
According to the reference provided:
- The most common axle diameters on mountain bikes are 15mm in the front and 12 mm in the rear.
- Front hubs use thicker axles (like 15mm) to increase the fork's torsional strength.
- Downhill and early thru-axle forks use 20mm front axles for added strength.
This means you'll most frequently encounter 15mm thru axles on the front wheel and 12mm thru axles on the rear wheel of many modern trail, enduro, and cross-country mountain bikes. The larger 20mm size is typically found on bikes designed for more aggressive riding, like downhill, where maximum front-end rigidity is crucial.
Here's a quick breakdown of common mountain bike thru axle sizes based on location and application:
- Front Wheel:
- 15mm Diameter: Most common on trail, enduro, and many cross-country bikes.
- 20mm Diameter: Used on downhill bikes and some older or specialized aggressive trail forks.
- Rear Wheel:
- 12mm Diameter: Most common on modern mountain bikes across various disciplines.
While the diameter is a key measurement, thru axles also have different lengths and thread pitches depending on the specific hub and frame/fork standard (e.g., Boost 148, Super Boost 157, non-Boost 142/100, etc.). However, the diameter (15mm, 12mm, 20mm) is the primary indicator of the axle type itself.
