James Parker - Is This Wheelie Necessary? - Up To Speed

Drawing The Line

How long will it be until streetbikes have MotoGP-style anti-wheelie controls? We don't have to wait until they're putting out 250 horsepower to start thinking about the problem.

Don't try this at home. In fact, don't try this at all: While riding your new 1000cc sportbike in first gear at 15 mph, open the throttle all the way, and keep it open. Don't tuck in, just sit up. Whether or not you make it to redline without flipping over backward, you'll learn that even a current 160-bhp superbike is acceleration-limited by its relatively short wheelbase and high center of mass-both compromises designed to give it agility and cornering clearance. Bolting on a longer swingarm and a shorter fork would reduce wheelies, but then your bike wouldn't go around corners.

Can we build really powerful bikes that won't wheelie? The short answer is yes. Using available technology, let's design a couple of anti-wheelie systems. First, we'll put a linear potentiometer on the fork, like the ones used to record suspension position on racebikes. This will tell us when the fork is at full extension as we accelerate, with the front wheel just coming up off the ground. We'll program an aftermarket ECU to cut back on the power at that point, so the wheel comes back down. So far it's a fairly crude system-we're cutting way back on acceleration.

The fork potentiometer is expensive and vulnerable to damage. So let's mount an accelerometer on the chassis and measure the acceleration at which the front wheel comes up. Then we can cut back power whenever we see this figure. This method is even less refined, as it doesn't take into account the rider's position and other factors such as fuel load.

Another way would be to measure the chassis pitch angle relative to horizontal, using a sensor to tell us when the front wheel has come up. This would allow us to carry the front wheel a few inches off the ground before we cut power. But again there will be problems, say if we are riding up and down hills.

Experimentation may indicate that we should use two or more of these systems together, giving more information to the engine control system about what the chassis is doing. We might begin with a harsh throttle chop that pitches the bike forward uncomfortably, and slowly refine the system to the point that the front wheel skims the ground as we accelerate, the throttle modulation almost unnoticed as the sensors provide continuous feedback and the engine makes the maximum power consistent with our design parameters.

So far, the chassis is passive. We just measure what it's doing and tell the engine how much power we've decided it can handle. By moving forward and back, the rider can change the center of mass, but the chassis doesn't help out.

In 1988 a co-inventor and I were granted a U.S. patent on a Motorcycle with Ride Height Suspension Adjustment. The bike (we didn't build a prototype) would have used a sensor to determine whether it was upright or leaned over and would have changed the shock mount positions of both front and rear suspensions accordingly, to give a lower ride height when being ridden straight and a higher ride height, for more cornering clearance, when leaned over.

This was essentially active suspension applied specifically to the problems of the motorcycle, with the center of mass automatically changed to meet the circumstances. By actively changing the chassis we could mimic a dragster when accelerating straight up and a roadracer when leaned over. Our patent looks crude by today's standard of electronic wizardry and millisecond adjustability, but it was feasible then and would be considerably easier to do today.

The ultimate anti-wheelie system for motorcycles might be an active chassis/suspension combined with effective engine power management. Traction control would be a factor, too, limiting wheelspin. With power brakes the software could eliminate wheelies with the rear brake instead of, or in concert with, the engine. Add ABS-you get the idea. Let's just be sure to put in a switch that can turn it all off so we can do the occasional monster wheelie.