Driving powerful rear-wheel drive sports cars used to be a bit of a lottery, especially in the wet. Get clever with the gas pedal on a big-horsepower car and you'd be chasing your backside quicker than you could say "massive oversteer." The rear would spin and overtake the front, and you'd be off the road in an instant.
It didn't take long for the auto firms to work out that their customers were, A: dumb and B: litigious. So as soon as they could, they produced clever "traction control" systems. These used the sensor hardware from the then-novel ABS systems appearing in the early 1990s to detect when the rear wheels were spinning faster than the fronts. The ECU then either cut the fuel injection or the ignition sparks to the engine, reducing torque and allowing the wheels to regain grip. Fewer yuppies killed themselves in BMWs and Porsches, driving got safer and (even) duller, and the engineers patted themselves on the back.
But now, nearly 20 years later, we face the same sorts of problems with sportbikes. The engines are making astonishing power, they're rear wheel drive and have instant throttle response. Plus, we only have one back tire. Double plus, when we're in a corner that single tire is leant over, reducing the grip available for acceleration even further. Aren't we the guys who need traction control?
The problem is that the task of running a suitable system to control traction on a bike has been largely beyond street bike technology-until recently. For a start, it's a much more challenging task than on a car thanks to complex factors like lean angles, suspension movement, the different radius of a tire as the bike leans over and the much finer control needed to keep a bike upright while moving. And, a car is completely stable; if you drove a car onto an ice rink you'd have no control over its movements, but it wouldn't fall over. Do the same on a bike and you'll be on your ass in no time because a bike in motion only stays upright because of a complex set of forces that are continually balancing each other out.
When you're leaned over in a corner, a force is generated between your tires and the ground. Since the bike is leaned over, its center of gravity isn't directly above the tire contact patches. That means some of the bike's weight is converted into a sideways thrust. The grip between the tire and the ground has to resist this thrust to hold the bike in a stable, leaned-over attitude. If there isn't enough grip to resist this sideways thrust the tires slip outwards...and you crash.
So the problem of grip while leaned over isn't just about preventing the engine or brakes from over-coming the acceleration and braking grip available to them. You also have to consider the effects of the cornering forces and their grip requirements too. Using too much of any one of these forces will reduce the amount of grip available to the others. So if you lean over there's less grip available to brake or accelerate hard. Exceed the total amount of grip available from the tires and you're going to crash. And while traction control can help avoid certain crashes, it will probably have much less effect on the number of bike crashes than it has had with cars.
How does it work?
In simplistic terms, the engine ECU measures the speed of the front and the rear wheels. If the rear wheel begins to spin faster than the front it assumes that the rear tire has lost grip and is beginning to spin. At that point the ECU will make changes to the engine to reduce its power output and hopefully regain grip. The ECU can retard the ignition timing, switch off the fuel injectors to one or more cylinders, or, if you have a ride-by-wire throttle (or a dual throttle valve system), the ECU can physically close the throttle plates. All of these methods will reduce the torque being generated by the engine and should allow the tire to regain grip. The rear wheel speed will come down and the ECU will return the timing/injection/throttle openings to their normal state and give full power back to the engine.
In the more complex situations that exist in real life, many other factors come into play. Wheel speeds will differ by a small amount when the bike leans over because the rolling radii of the tires vary as you lean, and weight transfer also alters this as well.
Like ABS systems, it seems like the best traction control will come from the firms who put the most effort into testing and optimizing the software driving the traction control systems. That, rather than hardware advances, will provide the best, most suitable traction control setups.