Head Tube Diameters
Head tubes can use one of several size standards
- Bicycles
The head tube of a bicycle is sometimes designated by the fork steerer column it accepts. This can lead to confusion, since head tube inside diameters are dependent on the headset standard. For example, frames that take one inch (25.4 mm) steerer columns can have three different inside diameters for threaded and threadless headsets (not including integrated-type headsets). The wide variety of integrated and non-standard, proprietary headsets that some frame manufacturers have created (and abandoned in some cases) makes listing all current and past head tube dimensions problematic. The following table includes the most common sizes; nominal head tube diameters are assuming a 0.1-0.2 mm interference fit, which is what most head tube reaming cutters are designed to bore. Adequate press fits are typically between 0.1 and 0.25 mm of interference.
| Steerer column nominal OD | Headset standard | Head tube nominal ID |
|---|---|---|
| 1"/25.4 mm | 1" JIS | 28.8 mm |
| 1" ISO | 30.0 mm | |
| 1" BMX/OPC | 32.5 mm | |
| 1⅛"/28.6 mm | 1⅛" standard, threaded and threadless | 33.8 mm |
| IS 1⅛" integrated 45×36 | 41.1 mm | |
| Campagnolo "Hiddenset" 45×45 | 41.9 mm | |
| Zero Stack/ Internal | 43.9 mm | |
| 1¼"/31.75 mm | 1¼" standard | 36.8 mm |
| 1.5"/ 38.1 mm | 1.5" standard | 49.6 mm |
- Motorcycles
Standard motorcycle head tubes and headsets are sized for a one inch (25.4 mm) diameter fork steerer tube.
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