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       Because of rake, the steering head actually rises and falls when the front end is steered.

       Steering Head Rise and Fall

      One of the interesting results of rake/trail is that the steering head falls slightly as the front end is pivoted from center to either side, and it rises as the front wheel is turned back toward center. The greater the rake, the more the rise or fall. You can see this for yourself. Straddle your bike, get it balanced vertically, and observe the elevation of the top of the steering head as you turn the handlebars from straight ahead to either side and back to center.

      Now, remember, gravity is pulling down on the bike, which is supporting perhaps half its weight on the steering head. So gravity actually helps turn the front end away from center and resists the front end returning to center. That’s not a problem, since steering head rise/fall can be balanced against other steering forces.

       Mass Shift

      While you are straddling your bike, you might also notice that when you turn the handlebars, the steering head also moves sideways (laterally). If you turn the bars to the left, the steering head (and the whole front of the bike) shifts laterally to the left of the contact patch. That means that when the front wheel is turned away from center, the weight on the front end is shifted toward one side. For instance, with the front wheel pointed toward the right, you’ll feel gravity pulling the bike over toward the right. In other words, steering from side to side can actually help balance the bike even if the wheels are not rolling. Of course, as the motorcycle begins to roll ahead, it reacts differently than it does when standing still. With the bike rolling down the street, everything moves around in a complex dance.

       Because of trail, the steering head moves sideways when the front end is steered.

       Contact Patch Location

      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.

       Tire Cross Section (Profile)

      With a narrow, round-profile tire, the CP doesn’t move far to the side. But with a wide, low-profile tire, the CP shifts farther sideways than with a round-profile tire, for the same lean angle. And the farther out the CP, the greater its off-center drag. The CPs of both front and rear tires shift laterally as the bike leans over, so the sizes and profiles of front and rear tires are interrelated. That’s one reason changing tires to different profiles, or changing just one tire to a different size or profile, can change how the bike handles, for better or worse. It’s very fashionable these days for cruisers to wear extremely wide rear tires, but handling usually suffers when function takes a backseat to style.

       When a wheel is leaned into a curve, the contact patch on the tire shifts toward the edge of the tread. CP shift is greater with a wide, low-profile tire than with a narrower tire.

       Self-Balancing

      With carefully selected rake, trail, and tire profiles, a machine can have good self-balancing dynamics, whether moving upright and straight ahead or leaned over into a curve and turning, and whether at fast or slow speeds. The point I don’t want you to miss is that the front-end geometry is designed to balance itself. If the bike leans over to the right, the CP shifts farther right, steering the front wheel more toward the right. As the wheel tracks away from center, that rolls the bike back toward vertical. When the machine returns to vertical, the gravity, steering head position, and CP all balance again.

       When the motorcycle begins to fall over, the location of the front tire contact ring moves slightly, increasing drag on that side of the tire and countersteering the front wheel back under the center of mass.

       As the front wheel steers

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