Yamaha is just about to change the future fate of motorcycle rally machines. Just like the 4 wheel drive rally cars a few years ago, the WR 450F 2-Trac demonstrated it's winning potential. It may seem obvious, that an all wheel driven vehicle would be superior on slippery or sandy surface. Nevertheless the technical development regarding weight, compactness and reliability is a big challenge and Yamaha is the only manufacturer to apply the 2 wheel drive technology on it's off road rally machines!
2-Trac is a ‘smart’ self-regulating system. Hydraulic pressure to the front wheel increases as the rear wheel loses traction on loose surfaces, and so the amount of power being transmitted to the front wheel is constantly changing so that the best ratio is always being applied. The front wheel can never spin faster than the rear wheel, and the amount of power transmitted to the front wheel is never greater than the wheel can use for traction. This self-regulating system also ensures that the hydraulic power supply to the front wheel is reduced as soon as the rear wheel regains full traction.
When the rider is coasting there is no power supplied to the front wheel – but if the throttle is opened sharply and the rear wheel starts to lose traction, the sudden increase in pump rotation speed boosts the fluid pressure within the system, and a significant proportion of the engine's power output is directed to the front wheel. If the rate of rear wheel spin continues to increase, the amount of power directed to the front wheel also increases, and so the proportion of engine power fed through to the front wheel is controlled by both the throttle position and the rear wheel's rate of spin.
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