An additional disturbing effect that makes corner braking difficult for the rider is the so called brake steer torque (BST, Figure 7). Due to the tire geometry, the tire contact patches move out of plane with the steering axis. If a brake force is applied, especially at the front wheel, the roll angle dependant contact patch offset to the steering axis generates a BST, that wants to turn the handle bars to the inside of the bend. As described in section 2, this leads to an upward roll movement of the bike, if the rider does not compensate the BST. Given a hazardous situation and high brake force gradients that can also arise from ABS activation, the BST gradient is so high, that the rider is not able to do so (see also Figure 2). Moreover, under shock, the upward roll movement of the bike might confuse the rider. The tendency of the motorcycle to leave its trajectory tangentially often leads to an even stronger application of the brakes, which in turn amplifies the negative side effect (see also quotes from [20]). In order to take these cornering specific challenges into account, a roll angle sensor is essential for future safety systems. 5.2 Approaches to Brake Steer Torque Optimized Corner Braking The BST that needs to be compensated by the rider can be written as: BSTrider = (Brake Force) * (Offset between Steering Axis and Tire Contact Patch) – Steering Damper Torque – Active Counter Steer Torque This equation shows four different means to approach the BST problem:
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