The Series B Rapide designed during the war and released to the press before end of hostilities looked radically different from the A. The oil pipes were now internal. Unit construction allowed Vincent to combine the engine and gearbox into a single casing. Philip Vincent summarised his frame design philosophy in his memoirs, writing "What isn't present takes up no space, cannot bend, and weighs nothing — so eliminate the frame tubes!" The angle between the cylinders was changed to 50° from the 47.5° of the Series A engine to allow the engine to be installed as a stressed member. This enabled Vincent to reduce the frame to an upper frame member (UFM) that was a steel box-section backbone that doubled as an oil tank, and to which the front headlug and rear suspension were attached. Brakes were dual single-leading shoe (SLS), front and rear. The wheelbase was shorter than the Series A, and its dimensions were closer to contemporary 500 cc bikes.