This friction plate was originally developed to solve some problems that were discovered when using an aluminium clutch back drum and pressure plate. These special racing items had to be used with a standard material friction plate, or their surfaces would be damaged. As the engine power outputs were increased this variation of clutch would begin to suffer, particularly after hard racing starts. If slipped by the rider to excess during a start it would often take one or two laps to recover and grip properly.
The Sintered Iron friction plate supplied by the Norman Hyde organisation would cause (when used under hard racing conditions) wear to the iron surfaces of a standard back drum and pressure plate, although the grip was superb and the clutch did not lose performance if heavily slipped on starting. In the search for reduced overall weight some alloy clutch components were then made by P&M Motorcycles. These were 'plasma' coated on the friction surfaces and because it was felt that the sintered iron clutch plate would rip these surface badly a different friction material was sought. AP Racing suggested the sintered bronze, as used in some of their competition car clutches and a suitable plate was produced. This plate has since proven excellent in original clutches.
The plate is slightly thicker than a standard item. Development and testing showed that the clutch gave the lightest feel to the hand, without any loss of performance, when the spring was set to be nearly flat during operation. Then, lifting the pressure plate would lift the spring 'over centre', and the lightest feel would be achieved. The Bronze plate is made at a thickness that generally achieves this result.
Copyright © 2000 Philip Pick
Version 0.1 Date January 2001