Thru Axle & Turbo Trainer Adapter Guide

Everything you need to know about mounting your thru-axle bike onto a wheel-on turbo trainer. Measure correctly, identify thread pitch, and find the right adapter.

What is a Thru Axle?

A thru axle is a thicker, more rigid axle – the common rear axle diameter is 12mm. Unlike traditional quick-release skewers that sit in U-shaped dropouts, a thru axle threads directly into the bike frame. The dropout on a thru-axle bike is a closed hole, not a U-shape. This design provides greater stiffness and stability, making it a favourite among mountain bikers and performance riders.

How to check if your bike has a thru axle: Look at the rear dropout. If it is a closed hole (rather than a U-shaped slot), your bike uses a thru-axle system.

How to Mount a Thru-Axle Bike onto a Wheel-On Turbo Trainer

You will need a thru-axle adapter that matches your bike's specific axle dimensions. Different brands and models use varying lengths and thread pitches, so it's essential to identify your axle's specifications.

How Do I Know What Size Thru Axle I Need?

Option 1 – Check the Stock Axle

Many bike brands print the size information (length and thread pitch) directly on the original thru axle. Look closely at the shaft or the head of the axle for engraved details.

Option 2 – Measure Three Key Dimensions

If no markings are present, take the following measurements:

• ① Thread Pitch: Place your axle threads against the thread pitch gauge (see image below) to determine if it is 1.0mm, 1.5mm, or 1.75mm.

• ② Diameter: Measure the diameter of the axle shaft (typically 12mm, but always confirm).
• ③ Overall Length: Measure the straight portion of the axle, including the over-locknut dimension (the total length that passes through the hub).

Selecting the Right Adapter for Indoor Training

Once you have the correct measurements, choose a thru-axle adapter specifically designed for turbo trainers. Use the adapter for indoor sessions, but always swap back to your original thru axle when riding outdoors to ensure safety and proper frame protection.