18 FEBRUARY 2006, Page 26

What drives Boris

From Alex Moulton

Sir: I was surprised to read that Boris Johnson, as a cyclist and historian, had not pondered on what had allowed the reduction of wheel size from the ordinary ‘penny-farthing’ with the crank drive to that of the conventional bicycle which he no doubt rides (Diary, 11 February). It is, of course, the chain drive with the larger chainwheel at the crank and a smaller sprocket at the hub which enables the revolution of the cranks to be independent of wheel size. The Starley ‘Safety’ incorporated this. Lord Hailsham was probably the first parliamentarian to enjoy the benefits of the yet further reduction of wheel size with the Moulton bicycle. He acquired this in 1964.

Alex Moulton

Moulton Bicycles, Bradford on Avon, Wiltshire