Proficient Motorcycling. David L. Hough
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Название: Proficient Motorcycling
Автор: David L. Hough
Издательство: Ingram
Жанр: Сделай Сам
isbn: 9781935484677
isbn:
What’s more, that twisty mountain road eventually comes to town. As you come off the hill and find yourself slogging through urban traffic, your biggest challenge might be avoiding a left-turning motorist or a car dodging the wrong way across a parking lot. So whether you ride conservatively or closer to the edge of the envelope, hard braking should be a part of your habit patterns. Rather than think of smooth as never using the brakes, I prefer to think of smooth as being able to brake right up to the limits of traction without upsetting the bike or getting excited, whether rounding a corner or negotiating traffic.
Inertia
Let’s consider how to make quick, painless, maximum-effort slowdowns. First, there are forces we’re trying to overcome with the brakes. Inertia is the physical property of objects wanting to keep moving in a straight line at the same speed. A speeding motorcycle wants to keep speeding along pointed straight ahead, even if we roll off the gas. What’s important about inertia is that it increases significantly with speed. Gravity is a constant—it’s the same regardless of speed. But the higher the speed, the greater the forward energy. To slow down a motorcycle or bring it to a stop, we’ve got to overpower its forward energy.
Of course the bike will slow down if you just roll off the throttle. Wind resistance, rolling friction, and engine compression braking all help overcome forward energy. But if you need to slow down quickly, you’ve got to use the brakes, and braking successfully requires both knowledge and skill.
Gravity is a constant that doesn’t change with increased speed, but forward energy increases dramatically with speed.
Braking Forces
You may have observed that rear-wheel braking can make lots of smoke and noise but doesn’t slow the machine nearly as quickly as the front brake does. Braking the wheel to a stop doesn’t necessarily stop the bike. That’s because the maximum braking force you can apply to a wheel depends upon traction, and traction is a function of the weight on the tire as well as the stickiness of the tire and roughness of the road.
Theoretically, if one-half of the total weight of the motorcycle, including rider and load, is carried on the rear tire, the maximum braking force you can get out of the rear tire is one-half the weight of the machine. So if the total weight is 800 pounds with a weight bias of 50/50, the maximum rear-wheel braking force would be 400 pounds However, since even rear-brake application transfers weight forward, rear-wheel brake force would decrease, encouraging the rear tire to skid.
Front-Wheel Braking
During braking, the load on the wheels isn’t a constant. When you apply the brakes, the weight seems to transfer forward onto the front tire, increasing front tire traction. Consider that whether it is engine compression or brake friction trying to overcome forward energy, the braking force is applied way down at the tire contact patches, while the center of mass is much higher on the machine. The mass wants to keep moving straight ahead, and the result is that when the brakes are applied, the motorcycle pitches forward. This feels as if the weight had suddenly been transferred forward onto the front wheel. Since the available braking force is determined by the load on the tire, as the machine pitches forward, more traction becomes available on the front. So more front-brake force can then be applied. Assuming tractable pavement and sticky rubber, it is relatively easy to brake hard enough on a light bike to do a front wheel stoppie, with 100 percent of braking force on the front and the rear wheel in the air.
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