The s1000RR's wheel speed...
The s1000RR's wheel speed sensor (attached to the perforated band on the rotor) helps calculate wheel speed and subsequently determine the necessary amount of traction control.
BMW's S1000RR has the most complex TC system on a current road bike. It has a number of different power modes to suit wet conditions: road use, normal track use and riding with slick tire fitments. In addition, it has a lean angle sensor so the ECU has more of an idea about the actual conditions and situation.
The system has two approaches depending on how far the bike is leaned over. When the bike is mostly upright, the ride-by-wire throttle system allows normal throttle performance, and if any rear wheel spin is detected it then retards the ignition to reduce torque and stop the spin.
But from 38-53 degrees (depending which mode you're in), the system actually reduces the amount of throttle that the ride-by-wire will allow, thus reducing the chance that the tire will spin in the first place.
The dash indicates the selected...
The dash indicates the selected power mode, and different levels of traction control are applied depending on the selection.
The system even acts to prevent wheelies (in certain modes) using the same underseat gyro that senses lean angle.
Ducati
Ducati claimed to be the first firm to offer "proper" traction control on its 2008 1098R. The system, called Ducati Traction Control (DTC), used front and rear wheel speed sensors, and when the ECU detected the rear wheel speed increasing compared with the front wheel it assumed the wheel was spinning and cut the ignition spark. The system worked well and offered eight levels of control to suit both scared novices and MotoGP stars alike. But because it cut spark, it allowed unburnt fuel into the exhaust system, which could damage the catalyst in the standard exhaust. To prevent this, DTC was only activated when you had a race kit ECU and race exhaust fitted.
For 2009, Ducati altered the DTC system so that it reduced power by retarding the timing of the ignition spark and the fuel injectors. This means there is no unburnt fuel in the exhaust, and therefore DTC can be activated on the street with the standard exhaust in place. DTC is available on the 1098R, 1198S, Multistrada 1200S and the Streetfighter S.
Bazzaz Performance
If you don't own a TC-equipped bike from Ducati or BMW you can actually add an aftermarket system. One of the best known and most advanced is the Bazzaz Performance Z-Fi TC, which is basically a bolt-on fuel management and traction control system. Its ECU samples engine RPM, throttle position and the selected gear several times per second, then determines how much it needs to cut the spark to maintain traction. It's a clever device with seemingly endless tunability, and has been used by numerous race teams.