The Veloce company is well regarded for producing some of the best single-cylinder motorcycles in race form and for private use. It is not so well-known that Veloce Ltd also produced some twin-cylinder machines: the Roarer, for racing, and the Model O for production. These bikes had many engineering features in common, such as twin contra-rotating crank shafts, inline cranks, shaft drive, and swing arm rear suspension. The supercharged Roarer was never raced because of the advent of war; this also put paid to the development of the Model O, which would have been the first so-called "Superbike." After the war, the Goodman family, owners of Veloce Ltd, focused on the production of a "Motorcycle for Everyman" - an idea that had featured in their production bikes since the formation of the company. They drew on the ideas embodied in the Roarer and the Model O to produce the twin cylinder LE range of motorcycles. These, however, were not well received by the motorcycling public, and many blame the production of the LE for the eventual demise of the company. The purpose of the book is to present, from an engineering perspective, an analysis of the Roarer and the Model O, comparing and contrasting the methods adopted by their designers to meet the different design specifications of these bikes, and to illustrate how the ideas developed in this exercise appeared in the LE range of motorcycles. The authors, Brian Agnew and Ivan Rhodes, met in the 1960s when Brian worked at Rolls-Royce Derby. They spent their weekends tinkering with motorcycles, and both have an intimate knowledge of the Velocette twins both from their time spent together and from their personal projects.