Читать книгу Proficient Motorcycling - David L. Hough - Страница 42

If you were to ride your machine through a puddle of white paint, you’d see a painted stripe all the way around the tread, maybe one or two inches wide. But even though we could see that this contact stripe is a big ring around the tire tread, it’s a lot easier to discuss front-end geometry if we agree to think of it as the small contact patch (CP) where the tire touches the road at any particular moment. Be aware that the location of the CP can shift forward and back as well as sideways.

Trail can decrease or increase as the front wheel rolls over a bump.

Consider what happens when the wheel rolls over a bump. As the tire first contacts the bump, the CP instantaneously shifts forward and then follows the bump backward until the tire rolls onto level ground again. If the bump is steep enough (a curb, for instance), the CP can momentarily jump ahead of the steering axis. That’s why a steep bump or dip yanks the handlebars around (and why riding no hands over bumps and grooves isn’t a clever idea).

Now, lean the bike over on the sidestand, with the front wheel pointed straight ahead. Get down on your hands and knees, and look back toward the front tire. Observe that the CP is no longer in line with the bike centerline. When you lean the bike over into a curve, the CP shifts laterally toward the direction of lean. That causes tire drag to steer the front wheel more toward the curve.