The terms ‘unit’ and ‘pre-unit’ are well-used by enthusiasts of classic Triumph motorcycles, as they neatly mark out pre and post-1957 models produced by the company. The decision in that year to combine the gearbox and crankcase, which had previously been separate units, was an inspired one, as it was to lead the way for all other British bike manufacturers in the years that followed. This month, Andrew Pollock lines up a pre-unit ’55 and a unit ’66 Triumph to indicate the advances that were made in the intervening years.
