Research was carried out on the braking effectiveness and its influence on motorcycle behaviour using an electronically controlled antilock braking system (hereinafter referred to as ABS). The ABS was equipped on a large-size touring machine (HONDA ST1100). Braking tests were carried out on a course with different mu levels, namely 0.99, 0.81, 0.62, 0.51, 0.39, and 0.19, for both the front and rear wheels independently. The allowable slip ratios of the tires were tested, for straight runs and turns, by setting the ABS to activate at different points. The ABS unit constituted wheel velocity sensors, an electronic control unit (hereinafter referred to as ECU), and a modulator for adjusting the brake calliper hydraulic pressure. Test results showed the following: (1) The braking effectiveness of ABS in straight runs, tested on road surfaces with high mu (.0.99) to low mu (.0.19) levels, showed deceleration rates exceeding 90%, compared to those of the riders' best braking values. The braking with ABS had only little influence on the motorcycle behaviour so that stability was maintained, even in cases where the tire slip ratios were relatively great; (2) The braking effectiveness of ABS in turns, whereby the mu value of the road surface was 0.39 and over, also showed favourable deceleration rates exceeding 90%, compared to those of the riders' best braking values. However, it was found that the stability of the motorcycle decreased depending on factors such as decrease in the road surface mu level, increase in the banking angle, and increase in the slip ratio.
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