The head tube holds the bearings which allow the front fork steer tube to pivot freely.
The steering axis angle, also called caster angle, is the angle that the head tube and hence the steering axis makes with the horizontal or vertical, depending on convention. The steering axis is the axis about which the steering mechanism (fork, handlebars, front wheel, etc.) pivots.
In motorcycles, the steering axis angle is called the rake and is measured counter-clock-wise from the vertical when viewed from the right side. A 0° rake would be vertical. For example, Moto Guzzi offers:
- a 2007 Breva V 1100 with a rake of 25°30’ (25 degrees and 30 minutes)
- a 2007 Nevada Classic 750 with a rake of 27.5° (27.5 degrees)
Traditional motorcycle head tubes and headsets are sized for a one inch (25.4 mm) diameter fork steering tubes.
- Chopper kit installation Guide. Retrieved on 2007-04-11.
- Motorcycle Cruiser How to Service Motorcycle Steering-Head Bearings. Retrieved on 2007-04-11.
- Motorcycle Maintenance. Retrieved on 2007-04-11.
- Moto Guzzi USA (2006). Retrieved on 2006-12-11.