tail" styled exhausts but this was replaced with the more conventional cylindrical silencer. High-level exhausts were made for the trials and off-road models, in which the only electrics are the magneto-powered ignition. Models This listing shows only the main variants and most models were available with refinements or in competition form. BSA had used a lettering system for their range of motorcycles and started the "D" series for their first two-stroke. The D175 was marketed as the B175 as BSA struggled against imports in the late 60s to its closure in 1972 (the larger capacity "B" series having helped make them the largest motorcycle manufacturer in the world). The engine size shown is nominal, British motorcycles were made 1 or 3 cc smaller than their tax bracket maximum to allow for re-bores and wear. Pre-1958 (D1 to D3) had 19 inch wheels and 4.5 inch brakes. The 1958 D5 had 18 inch wheels and 4.5 inch brakes. 1959 D7 and later models had 18 inch wheels and 5 inch brakes front and rear. Developments and models D1 The D1 (the original model) 125cc was available initially only with a rigid rear suspension, although within three years the range was enhanced to include an optional plunger rear suspension. The front suspension of all D1's possessed no damping and resulted in a bouncy ride quality. D1's were available with a variety of electrical lighting systems. Wipac systems were available either in 6v AC (known as direct lighting) or DC. The AC system used a small dry 'torch' cell battery to illuminate the forward facing 'pilot' bulb within the headlamp shell, the remaining lighting was only available for use when the engine was running and the dry cell had to be regularly replaced. The DC system incorporated a lead acid battery and operated in a conventional manner. For a short period some D1's were equipped with Lucas lighting systems and these operated in a similar manner to the Wipac DC system. The D1 continued to be available to the public right up until 1963 and was still produced for the GPO (General Post Office) for at least 2 more years. DELUXE/BD1: This model has specification identical to the standard D1 model, but has a black tank with chromium strip on top and cream side panels: black frame and mudguards: chromium plated rims: polished primary chain cover and is equipped with crash bars, legshiels