To measure bicycle forks, the most common method focuses on the Axle-to-Crown length.
Understanding Fork Length Measurement
When talking about bicycle fork size, the primary measurement is typically the length from the axle to the crown. This specific dimension is crucial as it affects a bike's geometry and handling characteristics.
Based on the provided reference, the more common method for specifying fork length on modern bikes is:
- Fork Length (Axle-to-Crown): Measured in a direct line from the fork crown (where the fork steerer tube meets the fork blades) to the axle (the center of the dropout where the wheel axle sits).
The reference also mentions Length-on-Axis, which is measured from the fork crown to the axle along the steering/head tube axis, but notes it as a less common method. Therefore, the standard measurement you'll typically use and encounter is Axle-to-Crown.
How to Measure Axle-to-Crown Length
Measuring the Axle-to-Crown length is a straightforward process.
- Prepare the Fork: If possible, remove the wheel. Ensure the fork is not under any load.
- Locate Measurement Points:
- Find the center of the axle slot (or eyelet) in the dropout. This is where the wheel axle sits.
- Find the point on the underside of the fork crown directly above the axle center.
- Measure the Distance: Use a rigid measuring tape or ruler to measure the straight-line distance directly from the center of the axle slot vertically up to the underside of the fork crown.
Measurement Points:
| Starting Point | Ending Point | Measurement Method | Resulting Length |
|---|---|---|---|
| Center of Dropout/Axle | Underside of Fork Crown | Straight Vertical | Axle-to-Crown Length |
- Tip: For accuracy, ensure your measuring tool is held perpendicular to the ground (vertical) when measuring a fork mounted on a bike, or measure parallel to the line where the steerer tube would be if the fork is off the bike.
This Axle-to-Crown measurement is the standard specification used to determine the length of a bicycle fork and is essential when replacing a fork to maintain the bike's designed geometry.
