Geometry Matters for Rake & Trail
You may have snoozed through geometry, but that stuff turns out to be quite useful after all.
It’s not unusual or strange to see someone being proud and happy about the rake of his bike. Yes, the extended fronts of our motors are really good-looking and the more raked the front end, the more it looks like a bike from a Hollywood production. However, the rake, as well as the accompanying term trail, are really important for the movement of the bike and every single degree of inclination can change the way we ride. Let’s see how, or if you want to skip fast forward, click on trail calculator. Example – a sportster chopper probably should have a trail a touch over 4″ .
Rake (the angle of inclination) is a term used to describe the angular relation between the head tube of the bike and an imaginary vertical line, drawn from the point where the head tube connects to the frame. The head tube of a bike with a rake of 0 degrees is perpendicular to the ground. Such a vehicle does not move properly as the front wheel stirs in a direction opposite to the force, applied to it. If the force is applied directly from the top, the wheel will just revolve at one place around its vertical axis and will never move.
However, if we change the angle of the applied force, moving it away from the imaginary line that is perpendicular to the ground, then the wheel would follow the line that starts under the axis of the wheel and ends in the point where the line that shows the direction of the force is projected on the ground.
The more force we apply or the less the angle between the line of this force and the ground, the more stable movement we achieve when ride in a straight line. However, if we reduce the force applied to the wheel or make the angle between the line of the force and the ground bigger, then the wheel will adopt a tendency of revolting in a circle around its vertical axis and the force of gravity that interacts with it from above may overcome the angular force.
This is the reason why your bike moves rather unstable even when on low speeds. If the driving force is reduced, the force of gravity will overcome it and this will result in your trying to cancel out the front wheel in order to keep balance. With the increase of speed the angle of application of the driving force also increases till it overcomes the force of gravity and despite the angle of inclination of the head tube and the high speed the control over the bike becomes unstable again as the angle of the driving force becomes almost parallel to the ground.
Trail, on the other hand, is a term that describes another variable, which strongly affects the control over the bike, and may be considered even more important than the rake. Trail is the distance, projected on a horizontal line at a ground level, between a point located under the axis of the wheel and a line that is in fact the extension of the longitudinal axis of the head tube. However, it is easier to explain the effect of trail on the control – more trail means the bike will be more stable and easily directed to move ahead, while less trail will make the bike less balanced and will require more efforts to control it. Usually sport bikes have less trail, which makes them more pliable, but more insecure. On the other hand, touring bikes and cruisers have more trail, which makes them more convenient and easy to ride.
Some specialists consider that a bike with perfect balance will have a trail between 3 and 4 degrees. However, some bikes need to be more flexible and others – more stable, that’s why it is better to determine the trail for each one separately, according to what it will be used for.
All in all, the combination of a certain trail and a certain rake determines the way your bike moves. Now, when you know how exactly these two variables affect the movement of your vehicle, you can change and adjust them according your own needs – depending on whether you want a more stable and easy to control bike, or more flexible and lively one.