A bike's rake, also known as fork offset, is a crucial measurement in its geometry, influencing how the bike handles.
Defining Bike Rake (Fork Offset)
According to technical definitions, rake or offset describes a specific distance on the front end of a bicycle. It is the distance between the axis of the headtube and the axis of the front axle, usually between 4 and 6cm. This measurement is primarily determined by the design of the bike's fork.
Essentially, the fork steerer tube aligns with the headtube axis. The fork blades then curve or angle forward, positioning the front axle a certain distance ahead of this axis. This distance is the rake or offset.
Why Does Bike Rake Matter?
Bike rake works together with the headtube angle and wheel size to determine the bike's trail measurement. Trail is the distance between the point where the steering axis (headtube axis) hits the ground and where the front tire contacts the ground.
- Higher Rake: Generally results in less trail.
- Lower Rake: Generally results in more trail.
The trail measurement significantly impacts steering characteristics:
- More Trail: Tends to make steering feel slower and more stable, often found on touring bikes or bikes designed for rough terrain.
- Less Trail: Tends to make steering feel quicker and more responsive, often found on road racing bikes.
Key Geometry Terms
Understanding rake is easier when viewed alongside related terms:
| Term | Definition | Impact on Handling |
|---|---|---|
| Rake/Offset | Distance between headtube axis and front axle axis | Influences trail |
| Headtube Angle | Angle of the headtube relative to the ground | Influences trail |
| Trail | Distance between steering axis ground contact and tire contact point | Determines steering stability |
By adjusting the rake, designers can fine-tune the trail for a desired handling feel, even if the headtube angle or wheel size is fixed. For instance, a fork with more rake can reduce trail, quickening steering on a bike with a slack headtube angle.
