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Spacing (Dropout, Axle)
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Frame spacing is the inside distance between the two fork ends (drop outs), where the wheel fits in. This can easily be measured just by removing the wheel and holding a ruler up to the space where the wheel came out.
Hubs come with various length axles, but the axle length is not as critical as the overlocknut distance, since it is the locknuts that actually contact the frame ends. Overlocknut distance can't be measured directly without a caliper of some sort.
This frame has a spacing of 125 mm
The dropout spacing of a frame must match the overlocknut distance of the wheels that are to fit it.
Some standard spacings:
| 91 mm | Low-end front hubs. |
| 96 mm | Older front hubs, especially French. |
| 100 mm | Modern front hubs. |
| 110 mm | Rear older track, coaster brake and other single-speed hubs. Also, front hubs for Downhill bikes with 20 mm axles. |
| 114 mm | Rear 3-4-speed . |
| 120 mm | Rear 5-speed, Ultra 6, newer track hubs. |
| 126 mm | Rear 6- and 7-speed (road). |
| 130 mm | Rear 7-speed (MTB) and 8- 9- and 10-speed (road). |
| 135 mm | Rear 7- 8- and 9-speed (MTB) |
| 140 mm | Rear tandem. |
| 145 mm | Rear tandem (newer models.) |
| 150 mm | Retro-Choppers, some Downhill and Freeride models. |
| 160 mm | Rear tandem (new Santana proposed standard.) |
Overall axle length for quick release hubs is commonly 11 mm longer than the overlocknut distance listed, 5.5 mm on each side.
In practice, the axle can be quite a bit shorter than this...even 1-2 mm protrusion past the locknuts will suffice to locate the axle properly, so, when converting a hub to the next wider spacing, it is usually not necessary to replace the axle.
In the case of steel-based frames, it is a fairly minor matter to re-adjust the spacing of a frame to make it fit a different width hub. This process is commonly referred to as "cold setting."
Re-spacing is not generally feasible with aluminum, carbon fiber or titanium frames.
See also my Article on Frame Spacing
