Читать книгу Proficient Motorcycling - David L. Hough - Страница 45

Two big contributors to straight-ahead stability are the inertial effect of the motorcycle /rider mass and the gyroscopic forces generated by the spinning wheels. Perhaps the best way to think of inertia is that objects “want” to keep on doing whatever they are doing. Kick a brick sitting on the ground, and you’ll discover that it doesn’t want to move. Throw the brick, and it’s obvious it wants to keep moving, at the same speed and in the same direction. The popular unscientific term for property of matter is momentum. The correct name for this is inertia, but if we start to add vectors and forces, we’d need to start calling it kinetic energy. To avoid a war over definitions, I’ll just call it forward energy.

Even if the front wheel tracks off on a tangent, forward energy attempts to pull the mass of bike and rider back into a straight line again.

A motorcycle, once up to speed, wants to keep rolling along, straight ahead, at the same speed. Forward energy contributes to straight-ahead stability by pulling the motorcycle’s mass back toward center and by providing a resistance against which the tires can react. For example, if the motorcycle starts to drift away from center, forward energy attempts to pull it back into a straight line again.

The wheels of a motorcycle also contribute to stability but in a different way. Spinning wheels generate gyroscopic energy that resists changes in position. A spinning gyroscope wants to stay spinning at the same angle. The gyroscopic effect of the wheels helps keep the motorcycle from making any sudden changes in direction.

There are four main forces acting on a motorcycle to cause it to roll (lean) toward the curve, and engineers have attempted to quantify them. It appears that tire traction is the dominant force that initiates the roll. The tire traction is balanced against gravity pulling the bike over, while rider steering input is balanced against gyroscopic stability. If it were not for the gyroscopic stability of the wheels, the rider would tend to overcorrect, and it would be very difficult to keep the bike balanced. This explains why a heavier front wheel steers more slowly than a lighter wheel does. A lighter front wheel assembly allows more flickable steering, which is an advantage on a race bike.