Motorcycle Steering
Any turn produces centrifugal force on the motorcycle, tending to make the bike lean to the outside of the turn. To balance this centrifugal force the Center of Gravity must be offset toward the inside of the turn. A left hand turn requires a lean to the left. A right hand turn requires a lean to the right. This applies to all turns, fast or slow.
What do we need to do to accomplish this?
Our aim is to transition from straight ahead riding to being stabilized in a turn.
If we intentionally move the contact patch line from vertically beneath the Center of Gravity, the bike will start to lean. For example, if while riding the bike straight ahead, we press on the left bar the front wheel points to the right. The front wheel tracks to the right (sometimes called “out tracking”). So the weight of bike and rider is now to the LEFT of it’s “support” on the ground, the tire contact patches. Because the weight is to the left, the bike leans to the left. It is important to note, for a LEFT turn, we initiate a lean to the left by pressing on the left bar, turning the front wheel to the RIGHT. This is often referred to as COUNTERSTEERING: a turn to the left initiated by turning the front wheel to the right.
The harder you press the quicker the lean; the longer you press, the further the lean angle.
Once the bike is leaned over to give the turn radius you want, ease pressure on the bar. Motorcycle steering geometry (primarily trail again), tire profile and other factors tend to keep the bike stable in the turn. Depending on a number of factors, the motorcycle may even track through the turn with no subsequent steering input (ie it may require NO steering force in the turn to keep the bike stable through the corner).
“Out tracking” works down to virtually zero speed. Once stabilized in a corner the front wheel will be turned to some degree in the direction of the corner. At higher speeds the steering angle will tend to “self adjust”, however at lower speed, for tight turns the steering may not “self adjust”, so, even though you are countersteering to initiate the lean you may need to turn the bars yourself in the direction of the turn once you are leaned over.
Once you are in a turn the lean angle can be adjusted by again countersteering until the angle is corrected. Press on the inside bar for more lean, outside bar for less lean.
Gyroscopic inertia and precession do factor in, again to a minor degree, in turning: turning the bars to the right will produce a precession force in the front wheel which would tend to lean the bike to the left. As gyroscopic inertia increases so does the force required to turn the handlebars and so does the resultant leaning force due to precession. Precession does not increase the magnitude of the force, it just translates the direction. The precession torque trying to lean the bike is always less than the steering torque the rider applies. Have someone sit on your motorcycle, now try and lean your motorcycle by lifting up on one end of the front axle, pulling inline with the fork tubes, and pushing down with the same force on the other end of the axle, again, in line with the fork tubes. This is the location and direction of the precession force. Even allowing for the fact your bars are longer than your front axle by perhaps four times, so giving around four times the torque or “twist” for a given force, you can see there is not much effect on your 500lb bike! Ever watch motorcycle racers on a track ride an
“S” bend? From leaned over full left to leaned full right in under a second. Imagine how hard you would have to pull up and push down on the front axle to do that!
Again with higher gyroscopic inertia you have to press on the bars harder or for longer, so even though you do get some precession help this is more than offset by the higher force or longer time required pressing the bars to get the front wheel to “out track”.
Also a front wheel with higher gyroscopic inertia tends to be heavy and that effects performance in other ways (Increasing the un-sprung weight….but that’s another story).
“Out tracking” uses gravity do the work for you. Ever fallen while walking on ice? If your feet slide to the right, YOU will “lean” to the left. This is effectively “out tracking”, moving your contact patch away from your Center of Gravity. This “lean” happens quickly: gravity is strong!
So there it is, a little deeper explanation of stability and steering!
Hopefully these ideas will help you get a greater understanding of what actually happens when riding a motorcycle. Understanding what is happening will hopefully help making riding safer and more fun!
If nothing else I’m sure you can now see why, during the Rider Course Instructors don’t have time to explain this tricky subject!
Ride Safe!
http://www.rider-ed.com/tips/motorcyclestability.htm