A combined brake system (CBS), also called linked braking system (LBS), is a system for linking front and rear brakes on a motorcycle or scooter. In this system, the cyclist's action of pressing one of the brake levers applies both front and rear brakes. The amount of each brake applied can be determined by a proportional control valve. This is different from the integrated brakes, where the application of pressure on the brake pedal only includes the application of some front brakes.
Legal Issues
In many countries, including the United States, the law requires that a motorcycle have two separate braking systems. The lever handle invariably drives the front brake, and the pedal actuates the rear part. Any bicycle with CBS should have two separate inputs for braking, though (as in the Honda VFR1200) each control independently operates the front and rear brakes. On the contrary, a car is required to have only one braking system for dynamic braking (ie, braking when moving), plus a separate parking brake.
The rationale for two separate braking systems is that, in comparison to cars, a motorcycle has a proportionately higher center of gravity, a shorter wheelbase, a higher power-to-weight ratio and a patch area of Smaller tire contact. All these factors lead to a much greater weight transfer to the front wheel in braking, and an increased risk of skidding. A rider must be able to use each brake independently to maintain control, and a CBS system seeks to further reduce any risk of slippage.