Measuring your handlebar is crucial for selecting the correct clamp size for accessories like bells, lights, or even stem clamps. The clamp size corresponds directly to the diameter of the handlebar where the clamp will be attached.
Why Measure Your Handlebar Diameter?
Handlebars come in various diameters, particularly at different points along the bar (e.g., the stem clamp area vs. the grip area). Accessories and stems require specific clamp sizes to fit securely without damaging the bar. Knowing the precise diameter ensures a proper and safe fit.
Methods for Measuring Handlebar Diameter
The most accurate tool for measuring handlebar diameter is a set of digital or dial calipers. However, you can also get a usable measurement using simpler tools.
Using Calipers (Recommended)
- Place the jaws of the calipers around the section of the handlebar where the clamp will go.
- Close the jaws until they snug against the bar without applying excessive pressure.
- Read the diameter measurement directly from the caliper display or scale.
Using a Tape Measure or String/Paper (Circumference Method)
If you do not have calipers, you can determine the diameter by measuring the circumference of the handlebar.
- Wrap and Measure: Use a flexible tape measure, a piece of string, or a strip of paper. Wrap it snugly around the handlebar at the exact point where you intend to attach the clamp.
- Mark the Circumference: If using string or paper, mark where the end overlaps the rest of the material. Then, lay the string or paper flat and measure the length from the end to the mark using a ruler. If using a tape measure, simply read the measurement. This length is the circumference of the handlebar at that point.
- Calculate Diameter: The relationship between circumference (C) and diameter (D) is C = 𝜋 * D. To find the diameter, you rearrange the formula to D = C / 𝜋 (where 𝜋 is approximately 3.14159).
As the reference states, "If you don't have callipers then you can use a simple measure tape. Just wrap around the bar at the point you want to attach the Oi to get the circumference size and then divide by pi (…. mmm) to get your diameter e.g. 99.9mm / 𝜋 = 31.8mm."
Example Calculation:
If you measure the circumference of your handlebar to be 99.9mm, you calculate the diameter as follows:
Diameter = Circumference / 𝜋
Diameter = 99.9mm / 3.14159
Diameter ≈ 31.8mm
This indicates you would need a clamp designed for a 31.8mm diameter handlebar.
Common Handlebar Diameter Sizes
While measuring is always best, knowing common sizes can help:
- Stem Clamp Area:
- 25.4mm (1 inch) - Older road and MTB standard
- 26.0mm - Classic road standard
- 31.8mm - Modern road, MTB, and hybrid standard (often called "oversized")
- 35.0mm - Newer, larger standard found on some MTB bars
- Grip/Accessory Area:
- 22.2mm (7/8 inch) - Standard for flat bars (MTB, hybrid, commuter)
- 23.8mm - Standard for road bars (where shifters/brake levers mount)
Always measure the specific section of your handlebar where the clamp will be located, as the diameter can vary along the length of the bar.
