If you attended the MotoGP event this year at Mazda Raceway Laguna Seca (or, if you are lucky, a round overseas), you no doubt heard many of the bikes coughing and sputtering as they miss on acceleration. This is not because of some mechanical problem, but rather the engine is cutting out momentarily as the bike's electronics limit power to the rear wheel for traction control.
Traditional, simple traction control has been around for many years, and even in the motorcycle world: Honda's 1992 ST1100 had such a system, but it was discontinued after several years. In basic traction control, front- and rear-wheel speeds are monitored with sensors. A loss of traction is indicated by the rear wheel turning faster than the front, and a control unit decreases power by any one of several available means until both wheels are turning at the same speed. It all sounds simple enough, but in two-wheeled racing there are many additional factors to consider.
A quick perusal of traction control systems in the automotive world shows how they have evolved over the years. Some setups control power by retarding ignition timing momentarily, others by cutting fuel. Still others directly control the throttle plate with a servo-motor, much like Yamaha's 2006 R6. And some even apply the brakes to individual wheels rather than cut power. Much of the advances are in cars with four-wheel drive because it's hard to detect a difference in wheel speeds if they are all spinning, and some innovative ways of determining a slip condition must be employed.
Other details in cars that must be considered (and have been overcome) are the difference in the outside- and inside-wheel speeds when the car is turning, how to apply the control if the driver is applying the throttle and brake at the same time (evidently a common occurrence) and near-instantaneous changes in wheel speed when the car goes over bumps or a small patch of ice. Suddenly, it's not so simple anymore. The patents for the various systems are filled with flowcharts and logic diagrams rather than parts drawings and schematics.
The problems are similar in the motorcycle world, but what's changed in recent years to overcome them is not the basic knowledge or technology but rather the computing and electronic capabilities that can now be harnessed in a small and lightweight package. The problem now is not so much implementing traction control but rather taking advantage of all this computing power. Aftermarket companies are increasingly offering ECUs which provide ignition and injection control, as well as data acquisition. From there, adding traction control becomes a software exercise more than anything.
Honda's mid-'90s ST1100 was offered with a traction control option, which measured and compared front- and rear-wheel speeds to determine how much to retard ignition timing and cut back engine power. | 
A tire's traction level peaks at a given amount of slip, which is counterintuitive to no wheelspin at all for best traction. Traction and optimum slip value can change for different types of pavement. Some traction control systems can learn over time to adjust automatically for changing conditions. | 
This data-acquisition graph shows rear-wheel speed, engine RPM and throttle position for Aaron Gobert's Graves Yamaha YZF-R1 at Willow Springs. You can see in long, looping Turn 2 Gobert accelerates to the point of wheelspin, where both traces go to a steeper slope momentarily and the front-wheel speed falls behind. Either signal can be compared to a maximum allowable slope for a given gear, rpm and lean angle, and this data alone used to activate traction control. In this case, a front-wheel speed sensor is not necessary. |