“Bonmartini boasted that his bike would be ‘a two-wheeled Bugatti’”
MAT OXLEY
Motorcycling’s most popular engine configuration celebrates its 100th birthday this year. For the last 50 years or so the inline-four engine has been the most popular configuration in sports and racing motorcycles. Indeed by the 1970s, when Japanese brands dominated the motorcycling landscape with inline-fours, someone came up with the term Universal Japanese Motorcycle (UJM) to highlight its omnipresence.
The first inline-fours were built at the dawn of the last century, with the cylinders arranged longitudinally in the chassis. This caused two problems: an impractically long wheelbase and overheating of the rear cylinders.
In 1923 two young Roman engineers had the bright idea of rotating the engine by 90 degrees, so the cylinder bank sat transversely. Piero Remor and Carlo Gianini worked in a tiny office near the city’s Piazza Barberini, where they drew up their first effort, a short-stroke, bevel-driven overhead-cam 490cc four that made 28bhp, three times as much as BMW’s newly launched R32 boxer twin. Remor and Gianini knew they were onto something, so went looking for money. They found investment from racer and World War I aviator Count Giovanni Bonmartini, who had recently established Compagnia Nazionale Aeronautica. Thus the engine got its first (of many) names: GRB, an acronym of the trio’s surnames.