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Proficient Motorcycling. David L. Hough
Читать онлайн.Название Proficient Motorcycling
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isbn 9781935484677
Автор произведения David L. Hough
Жанр Сделай Сам
Издательство Ingram
If you watch a motorcycle cruising down the superslab (freeway), you’d swear it follows an absolutely perfect straight line. But if you could measure accurately, you’d discover that it rolls ever so slightly from one side to the other as it balances itself, sort of like a clock pendulum. This self-balancing act is more obvious at slower speeds because the front tire requires greater steering input at slower speeds than at higher speeds to get the same effect.
If you were to ride your bike slowly through a puddle of white paint and then go back and look at the tire tracks, you would observe that the front tire sometimes tracks to the left and sometimes to the right. In other words, the front tire rolls along in a snakelike track as the bike continuously rebalances itself.
Gyroscopic and Inertial Stability
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.
What Makes It Turn?
In the previous section, I discussed a number of factors that cause a motorcycle to balance itself and what the rider can do to help. Now, let’s consider what we do to make a motorcycle turn. I’ll try to keep turning as understandable as possible and still give you the information you need to achieve better control of your motorcycle.
Turning Equals Unbalancing
As already noted, a well-engineered motorcycle wants to go straight. The front-end geometry automatically steers the bike toward straight ahead and vertical, and forward energy and gyroscopic forces help stabilize it. To get a two-wheeler to turn, we need to get it leaned over. So turning is really a process of unbalancing the bike to get it leaned over, then rebalancing again in a curving path.
Turning is really unbalancing the bike to get it leaned over, then rebalanced in a curving path.
Bikes Versus Cars
One of the big differences between how two-wheeled motorcycles and automobiles turn is that a motorcycle must first be leaned over before it starts to turn. An automobile starts to turn as soon as you yank on the steering wheel. The same is true for a trike or sidecar outfit, or for any other multitrack vehicle. But two-wheelers are different. Even with a flickable sportbike, it may take a half second to get the bike leaned over before it actually starts to change direction. And with a heavyweight tourer, that initial lean may require more than one second.
A lot of arm-waving and heated discussion has taken place around the campfires and Internet forums about how we really cause motorcycles to turn. The discussions always get around to countersteering, but there doesn’t seem to be much common understanding of what we really mean by countersteering and exactly what the forces are that make it work. Let’s see if I can clear up some of the mystery.
The Leaning/Cornering Process
Leaning can be initiated by a number of different factors, including rider’s body English, steering the handlebars, and even road camber or a crosswind. The most powerful input is steering the handlebars, so we’ll focus on that first.
Experienced riders usually refer to a rider’s steering input as countersteering because the handlebars are steered opposite, or counter, to the intended lean. Push on the right grip to lean right; push on the left grip to lean left. That’s where some of the confusion starts because leaning and cornering is really a process of several steps, whereas countersteering is only the first very brief step in the process. The leaning/cornering process all happens within a couple of seconds, so let’s slow down the action and go through it step by step. We’ll illustrate this from the front and exaggerate the graphic a bit so you can understand what the front end is doing.
The rider initiates the lean by a brief press on the grip to steer the front wheel away from the intended direction of turn. From the saddle, it may appear that the front wheel continues in a straight line while the top of the bike leans over, but what really happens is that the front wheel steers off on a slight tangent, which causes the contact patch to track away from the turn. The bike’s mass resists lateral movement, so the tire tracking out forces the top of the bike to lean in toward the turn. For example, let’s say the rider wants to make a right turn. Pushing on the right grip steers the front wheel off more toward the left, which forces the bike to lean toward the right. The actual countersteering takes only about a half second for an aggressive lean, or one second for a leisurely lean. Let’s use the term roll in place of lean, to borrow an aviation term that’s a little more descriptive.
If you have been practicing countersteering for a while, it may seem as if you just press on the grip and maintain the same pressure. But it should be obvious that if the front wheel continues to track off on a tangent, the bike will continue to roll over until it slams into the ground. So as soon as the bike rolls toward the turn, you must ease up on that initial countersteering push to allow the front wheel to steer itself back toward center. If the bike rolls over too far, you actually add some pressure on the grip to stop the roll and stabilize the lean angle. The gyroscopic stability of the wheels helps smooth out the steering input.
Approaching a right turn, the rider momentarily countersteers the front wheel away from the turn. The front wheel tracking left forces the bike to roll right.