I'm thinking of friction drive for my next electrically assisted bicycle by means of a roller driving the tyre. It used to be common practice to makesuch a roller of carberundum material, in fact they were probably small grinding wheels. Does anyone know of any better material? I wonder if any more modern material, plastics for example, would have a higher coefficient of friction against rubber bicycle tyres. Power transmitted is in the order of 500W. Jim Lugsden.