Proficient Motorcycling. David L. Hough
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Название: Proficient Motorcycling
Автор: David L. Hough
Издательство: Ingram
Жанр: Сделай Сам
isbn: 9781935484677
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This isn’t something new because it’s how everyone steers motorcycles, whether they realize it or not. Lots of riders concentrate on body English such as knee or foot pressure, unaware that the important input is through the hands. Accurate cornering is much easier once you realize that the primary input is through the grips. But once you’ve experimented with push steering, it’s time to move on. Different machines and different situations provide different feedback to the grips when leaned over in a corner. So we need to understand countersteering as more than simply pushing on the low grip.
Out-Tracking
When you countersteer, it may seem as if pressure on the grip pushes the bike over without actually pivoting the front wheel. Does the front end actually pivot away from center as the bike leans over into a curve? Yes. The movement is slight, but if the front end isn’t free to pivot in the steering head, the motorcycle can’t be balanced or turned.
If you could watch a slow-motion video of a motorcycle running through a puddle of paint and then making a turn, you would see that the front tire momentarily tracks toward the outside during the initial countersteer, then eases back toward the direction of turn. In slow-speed turns, the front tire generally tracks outside the rear tire.
When the rider countersteers, the front wheel momentarily out-tracks opposite the intended direction of the turn, then returns to center as the motorcycle leans over.
If you’d like a good example of out-tracking, record some motorcycle road race footage, and play it back in slow motion. In those shots where the camera is looking back down the straight toward a corner, you can see the lean angle of the bikes head-on. If you mentally plot the path of the motorcycle’s center of mass, you’ll see that the bottom of the front tire out-tracks, even arcing over onto the rumble strips as the rider uses every last inch of pavement to get the bike leaned.
Coning
While your bike is leaned over in a curve, you might wonder why the bike continues to turn even though the front end seems to be pointed straight ahead. Part of the reason is that the front wheel really is pointed slightly toward the curve. The other part of the reason is called coning. To understand the concept of coning, let’s consider the shape of the front tire where it meets the road surface.
The motorcycle pictured above is in a straight line, approaching the turn-in point.
As the rider countersteers, the front wheel actually tracks away from the intended direction of turn.
With the motorcycle leaned, the front wheel recenters and then steers toward the turn.
When the wheel is leaned into a turn, the flexible tire forms a contact ring that is conical in shape, similar to the shape of a foam coffee cup on its side.
Although we can see that the top of an inflated tire forms a rounded shape, we have to imagine that the tire momentarily gets flattened where it contacts the ground at the CP. And we also know that the tire CP isn’t really a single point but rather a continuous ring around the tread. It’s important to recognize that with the bike leaned over into a turn, this contact ring forms a conical shape, similar to a foam coffee cup on its side.
If you nudge the cup forward, it wants to roll in a circle because the circumference at the closed end is smaller than the circumference at the open end. If you stick a toothpick through the center of the cup bottom, the toothpick will point approximately at the center of the circle. A motorcycle tire responds similarly when the bike is leaned over, with the inside of the tire contact surface covering less distance than the outside. So when leaned, a motorcycle wheel wants to roll in a circle, with the axle pointed more or less at the center of the turn. In a very tight turn, the axle may actually point at a center that’s below the surface of the ground.
Fast Flicks
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.
U-Turns
If you’re paranoid about slow speed U-turns, you’re not alone. Heavyweight machines can be a handful at slow speeds and in tight quarters. The novice technique is to drag the foot skids, turn the bars to the stop, and feather the clutch to creep around. The novice may also discover that the bike has a larger СКАЧАТЬ