Motorcycle disc brakes are the subject of widespread complaints of severely degraded and unpredictable performance in wet weather. Complaints refer not only to the reduced power of the brake, but to the considerable delays (of up to 3-4 seconds) before any braking action starts. U.S. and Australian federal vehicle standards and design rules are inadequately framed to cover this. The house of representatives standing committee included in their may 1978 report on motorcycle and bicycle safety a recommendation (para. 72) to revise the braking design rule (ADR 33) and to carry out appraisals of remedial measures (para. 67) for wet weather disc brake performance loss. This report covers suitable test procedures and reviews the relevance and value of modifying pads and discs. An expanded summary of material and discussions of the TRRL seminar on wet braking held on 19th September, 1978 is included with emphasis on the reported effectiveness of sintered metal brake pads. The NHTSA office of defects investigation of Honda gl 1000 and cb 750f models which led to the adoption of grooved pads is also covered. Recommendations for road user research and revision of vehicle braking standards are made. (a)
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