Measuring a rear wheel axle primarily involves determining its compatibility with your bike's frame. The most common measurement needed is the distance between the inner faces of the frame's rear dropouts, which is known as the Over Locknut Dimension (O.L.D.). This dimension indicates the required width of the hub that the axle passes through.
Understanding Over Locknut Dimension (O.L.D.)
O.L.D. is a crucial specification when matching a wheel or hub to a bicycle frame. It represents the spacing needed for the hub/axle assembly to fit correctly between the frame's rear dropouts. While often associated with the hub, it directly relates to the axle and how it interfaces with the frame.
How to Measure Rear O.L.D.
The method for measuring O.L.D. depends slightly on the type of axle system (quick release or thru-axle), but the principle is the same: measure the internal width of the frame's dropouts.
- For Quick Release (QR) or Solid Axles: Measure the width from the outer edge of one locknut or spacer on the hub to the outer edge of the locknut or spacer on the other side. This measurement should match the internal width of your frame's dropouts.
- For Rear Thru-Axles: As per the reference, this is measured from the inside to inside of your frame at the drop-outs. This gives you the exact O.L.D. required for the thru-axle hub to fit correctly.
To perform the measurement on your frame:
- Use a ruler or, ideally, a caliper tool.
- Place the measuring tool between the inner surfaces of the rear dropouts.
- Note the distance in millimeters (mm).
This measured distance is the O.L.D. your rear wheel and its axle must match.
Other Axle Measurements
While O.L.D. is key for frame compatibility, sometimes other axle dimensions are also relevant:
- Axle Diameter: This refers to the thickness of the axle itself. Common diameters for rear axles include 10mm (for many QR and older solid axles) and 12mm (common for rear thru-axles).
- Axle Length: This is the total length of the axle from end to end. This measurement is less critical for frame compatibility (O.L.D. handles that) but is needed when replacing just the axle itself or selecting a thru-axle skewer (which has a specific length and thread pitch).
Common Rear O.L.D. Sizes
Knowing common O.L.D. sizes can help identify what your bike likely uses:
| Axle Type | Common O.L.D. Sizes | Notes |
|---|---|---|
| Quick Release | 130mm, 135mm | Road bikes (130), MTB/Hybrid (135) |
| Thru-Axle | 142mm, 148mm (Boost) | MTB (142, 148), Road/Gravel (142 often) |
Selecting a wheel or hub with the correct O.L.D., diameter, and type (QR or thru-axle) is essential for proper fit and safe riding.
