The R259 1,085 cc flat-twin engine has a maximum output of 90 horsepower (67 kW). The engine was named "Oilhead" as it had air-cooled cylinders but oil-cooled heads.
The BMW R1100RS used a frameless design, using the engine as a stressed member, an approach used by BMW for all subsequent oilheads (except the R1100S). Instead of having conventional telescopic forks, the R1100RS used BMW's own Telelever suspension which bolted directly to the engine. The Telelever design has a superficially similar appearance to telescopic forks, but braking forces are taken back horizontally, minimising "fork dive". A rear subframe supported the rider, passenger and luggage. Both fully faired and half-faired variants were available.
In 1993 the engine was adopted for the R1100GS. In 1999, a more powerful six-speed version of the R259 engine was fitted in the BMW R1100S. In 2013 BMW introduced liquid-cooling for their flat-twin motorcycle engines, but the company still fit oilhead boxer engines to roadsters such as the R nineT and the R1100R.
^ abEdwards, David (October 1994), "Best standard bike: BMW R1100GS", Cycle World, 33 (10): 45
^ ab"BMW history: BMW celebrates its anniversary / the new boxer". BMW Motorrad. Retrieved 2013-05-19. 70 years after the R 32 of 1923, BMW presents the BMW R 1100 RS sports tourer at the beginning of the 1993 season, the first model of the new boxer generation, followed one year later by the Enduro model BMW R 1100 GS.
^Bill Stermer (July 2005), "2005 BMW R1200ST", Rider: 42, As with all oilhead BMWs ... the engine functions as a stressed member; various subframes solidly mount to it to support the fork, seat and related components.