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 1.4.2 Which Torso-Arms-Handlebar geometry work best:

a) One of the worst Torso-Arms-Handlebar steering geometry:

Road and road-racing bicycles have 'C' shape handlebars and even 'handlebar extensions' that mount in the center of the handlebars.

The Torso-Arms-Handlebar geometry of such 'C' shape handlebars is such that a small torso leaning angle generates a large orientation of the front wheel. So when the rider leans his torso in a curve, the arms flex due to the gyroscopic counter-reactions of the front wheel. Thus, the 2-Wheeler servomechanism reacts slowly, sluggishly and imprecisely to the rider torso's controlling inputs.

The central 'handlebar extensions' are even worst since the torso leaning translates into no front wheel orientation. The bicycle steering then only relies on the torso weight leaning right or left, and corresponding front wheel gyroscopic reactions, to turn right or left. These reactions are strong and 'fast' at high speeds, but not at 'low and medium' speeds.

b) Another worst Torso-Arms-Handlebar steering geometry:

As a general rule, if the rider's elbows can flex, the torso leaning will only sluggishly cause an opposite orientation of the front wheel. This is like inserting a slowing 'Time Constant' in the open loop of the steering servomechanism. (In fact, the servomechanism block diagram and the mathematical model would certainly benefit from adding the flexibility of the arms, which is a factor that becomes increasingly more important as speed and gyroscopic counter-reactions increase.)

On a motorcycle where the rider is too tall for the motorcycle or sits forward too much, the rider's elbows may be flexed as much as 90 degrees and are then even more 'flexible'. An example of the rider sitting forward too much is on a motorcycle where the rider sits forward closer to the wind screen, in order to get more protection against rain or cold. Another typical and potentially more problematic example, because the vehicle is more heavily loaded, is on a touring motorcycle where the rider sits forward more, in order to leave room for his rear passenger. Things work well going straight on a highway due to the front wheel's strong gyroscopic stability, but emergency maneuvers will certainly be slow and imprecise.

Curiously, 'custom' motorcycles with higher handlebars have an acceptable steering geometry: When the rider leans to one side, he solidly pulls on the opposite steering handle, so that the front wheel reacts instantly. However, a first problem with these motorcycles rather comes when the front wheel extends far forward. The extended wheelbase then generates weaker centrifugal correcting forces. This  translates into higher minimum stable speeds WITH and WITHOUT hands on the handlebar, with the associated difficulty riding at slow speeds in town or in parking lots. A second problem with these motorcycles is that the small front wheel is associated with a small front brake that do a poor job at stopping the motorcycle.

c) Some of the best Torso-Arms-Handlebar steering geometries:

The best steering Torso-Arms-Handlebar steering geometries are the ones of mountain bikes and off-road motorcycles: The large straight handlebar insure that torso leaning induces precise and fast front wheel orientation with little elbow flexing. Such Torso-Arms-Handlebar steering geometry are very well adapted to the job of riding slowly around obstacles on the ground.

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