Читать книгу Proficient Motorcycling - David L. Hough - Страница 57

The more muscle you put into countersteering, the harder the front tire will push to roll the bike into a lean, and the quicker it will roll (up to the limit of traction, of course). The longer you hold pressure on the grip, the farther over the bike will roll. Those are key points to remember when riding a twisty road where you need to flick the bike left-right-left in a series of turns. Remember, it may take a half second to get the bike rolled upright from a tight turn and another half second to get it leaned over the other way before it changes direction.

Is it possible to muscle the handlebars hard enough to snap the tires loose? Yes. You may have seen this in a road race, where a bike suddenly jumps into a heart-stopping wiggle in the middle of an S-curve, or the front tire loses its grip and the bike crashes off on a tangent. In an aggressive S-turn, the rider needs to counteract the roll when the bike is leaned to the desired angle, and that demands some traction.

A motorcycle rolls around its center of mass (CoM) without a lot of resistance but resists being pushed up, down, or sideways. That’s why a bike speeding over a lumpy bridge on the Isle of Man can get airborne. The bike’s mass wants to keep going straight ahead, even as the ground drops away beneath the tires.

Even if you aren’t flying over a steep bridge, the bike’s inertia will momentarily resist gaining or losing altitude. When a bike is leaned over into a turn, the CoM must lose altitude. The bike’s inertia momentarily resists the pull of gravity, so the tires will have reduced traction when rolling toward the turn. But when rolling the bike up out of a turn, the CoM must be lifted up again, momentarily increasing traction. As the bike is rolled upright, you may notice that suspension compresses, at least for a moment.

The practical application of this is that the front tire is more likely to lose traction when the rider is countersteering hard into a turn, and the tire gains traction as the bike is rolled back to vertical. It also explains why it takes more muscle to roll a bike up out of a lean than to roll it into a lean.

As the motorcycle is rolled into a lean, the mass has to drop slightly to maintain contact with the road. That can cause a temporary reduction in traction. When the bike is rolled up out of a lean, the bike’s mass has to be lifted vertically, which demands more muscle but results in a temporary increase in traction.