The Wheelie Is The Enemy

How can you accelerate harder when you’re already flipping over backward?

Valentino Rossi Sepang test action
Valentino Rossi, Movistar Yamaha, Sepang International Circuit, February, 2017Courtesy of Movistar Yamaha

Valentino Rossi made his famous remark, “The wheelie is the enemy,” a few years ago, but the message is still clear. The upper limit of acceleration on a motorcycle is set by point when that front wheel is lifted off the pavement by the engine’s torque on the rear wheel. The higher the front lifts, the easier it becomes to lift it farther. The acceleration at which this takes place is the “wheelie limit.” To accelerate harder than this, some way must be found to increase the load on the front of the bike, sufficient to put the front tire back on the pavement.

Electronic anti-wheelie systems are useful to riders because they can prevent loss of steering control caused by engine power suddenly yanking the front wheel off the pavement mid-corner. Because they bring the front end down by momentarily reducing engine thrust, such systems can do nothing to raise the wheelie limit.

Valentino Rossi Valencia test action
Valentino Rossi, Movistar Yamaha, Valencia IRTA Post-Season Test, 2016Courtesy of Movistar Yamaha

Increased acceleration was the goal of the recently banned MotoGP “winglets,” the purpose of which in 2016 was completely different from that of wings and other aerodynamic downforce devices used on Formula 1 cars. On cars, downforce presses the tires harder against the pavement, thereby generating higher cornering grip than could the car’s unassisted weight alone. On a MotoGP bike, the winglets, mounted as near as possible to the front of the fairing, were put there to maximize acceleration by holding the front tire down on the pavement.

Notionally seeking a similar result was the supposedly Ducati invention and patent of a system to generate anti-wheelie torque by converting exhaust gas flow into jet thrust via a nozzle. Such applications were common on high-speed, piston-engine-powered aircraft in World War II. A rough estimate for a MotoGP application, with exhaust directed straight rearward at seatback height, suggests that 40 pounds of thrust, located as high as possible above the center of mass of machine and rider, might create a useful anti-wheelie torque. It would become more effective if directed straight up, as far forward on the bike as possible. Think of it as analogous to an attitude thruster on a spacecraft. Of course, there would be some change in engine performance as a result of any restriction of exhaust flow.

Dragsters solve the wheelie problem with long wheelbase. By moving the center of mass of bike and rider forward with an extended swingarm, you can create an anti-wheelie torque as large as you like (unless class rules say otherwise). But the huge driving force of hot dragster tires many inches wide, heated moments before use, is not available on a roadrace bike.

Andrea Dovizioso Motegi Race action
Andrea Dovizioso, Ducati Team, Twin Ring Motegi, 2016Courtesy of Ducati Team

Back in 2008, when Rossi had just switched from Michelins to Bridgestones, his data system showed in practice at Mazda Raceway Laguna Seca that he was having to brake 46 feet earlier with the ’Stones than with the previous French tires. Nothing worked to fix this until crew chief Jeremy Burgess raised the bike. With the original ride-height settings, when Rossi pulled the lever, the front tire slid rather than gripped. But when the bike was raised a bit, weight transfer to the front tire was able to build up in step with braking force.

Steering is another reason long wheelbase isn’t a solution to the wheelie problem. The longer the wheelbase, the slower your steering becomes (because the wheelbase is the “lever” by which the front tire swings the whole bike to a new direction). A compromise results, which is why we don’t see any 52- or 59-inch wheelbases on the starting grid. Two-wheel steering would be a possible but complex way around this slow steering problem.

Jorge Lorenzo Sepang test action
Jorge Lorenzo, Ducati Team, Sepang International Circuit, February, 2017Courtesy of Ducati Team

Another anti-wheelie possibility is suggested by the common Supercross move of tapping the brake in mid-air to rotate the whole bike forward, as a means of correcting its landing attitude. To raise the nose, the rider gives a whiff of throttle. On a roadrace bike, this could take the form of a flywheel, rotating in the same direction as the wheels and in their plane, accelerated to high speed either by braking or by an electric motor. When anti-wheelie torque was required, you would brake the flywheel. The obvious drawback is the weight of the flywheel and associated hardware. Compromise again. When we want more and more from a basically simple system (two wheels, an engine, and a place to sit), the virtue of its simplicity is lost.

For the moment, that leaves us with what good riders do instinctively: pull their weight forward on the bike with the strength of their arms to keep the front end down during maximum acceleration. If the rider in full gear weighs 170 pounds and can move forward six inches, that suggests a maximum anti-wheelie torque of 170 x .5 = 85 lb.-ft. (the actual result will be less than this because hands and feet can’t move forward).