The BMW R90S is a 900cc sport motorcycle produced by BMW from 1973 to 1976. BMW commissioned designer Hans Muth to oversee the R90S, which became the flagship of the boxer engined "/6" range. Sporting distinctive two-tone paintwork, a bikini fairing and a new tail, the R90S was intended to shrug off the enduring image of BMW bikes as staid and utilitarian. The R90S had a top speed of , it ran the quarter mile in around 13.5 seconds and it accelerated from in 4.8 seconds. Maximum torque was delivered at 5,500 rpm and the engine redlined at 7,200 rpm. Technical overview The R90S' type 247 "airhead" engine was a pushrod OHV, two valve per cylinder, air-cooled flat-twin "boxer" unit. The engine was based closely on the R75/5, sharing the same stroke, but with a larger bore, to give a capacity of 898cc. The R90S weighed and has a five-speed gearbox with a shaft final drive. The first R90S models had a two-tone paintwork scheme of "Smoke Black/Silver" with adhesive gold pinstripes. Feedback from unimpressed customers prompted BMW to return to hand painted pinstripes. Later R90S models were available also in two-tone "Daytona Orange" with red pinstriping. The R90S had a redesigned seat, with a small "ducktail" fairing which (in addition to an underseat tool tray) provided a small storage space for lightweight items such as waterproofs. Standard equipment included a full toolkit, a hand pump, a first-aid kit and even a small hand towel with an embroidered BMW logo. The R90S had a small bikini fairing which housed two analogue instruments: a clock and a voltmeter. Its 238 watt alternator was later upgraded to 250 watt. An adjustable hydraulic steering damper was manually adjusted via a knob on the steering head. Suspension was by long-travel telescopic forks and twin rear shocks whose rear dampers were adjustable for preload (the only suspension adjustment available). Whereas other BMW boxers had Bing slide constant velocity carburetor, the R90S was fitted with accelerator pump Dell'Orto carburetors. The R90S engine had a 9.5:1 compression ratio, while the less sporty R90/6 had a ratio of 9:1. The alloy wheels were spoked and wore tubed tyres. The front brake had twin 230 mm disks and ATE callipers; the rear brake was a 200 mm SLS drum. The R90S and the other BMW "/6" series front brakes had an unusual system whereby a master cylinder on the