"The R90S was a sport bike produced by BMW. It was first introduced in 1973. The R90S is considered by many to be one of the first superbikes, and the first such machine from BMW. The first U.S.A. AMA Superbike Championship was won in 1976 by Reg Pridmore riding a R90S. This type of engine is a 247 BMW and known as Airhead (motorcycle). It is especially well regarded amongst sportbikes from 1973-1976. Overall, it is the definitive 'airhead' BMW as regarded by owners and fans alike.
The bike's stunning visual design was overseen by Hans Muth, who was brought into the BMW fold to create a machine with a unique presence far removed from the staid image offered by previous BMW offerings such as the fast, well built, but conservative R69S. This designer later went on to design the R65LS, and also the Suzuki Katana. The R90s possessed a redesigned seat, with a small, styled ducktail, which was regarded by some as a retrograde step for those that rode two up (given the relative comfort of the previous Denfield double seat on the standard /5/6 machines). However, this ducktail added a second underseat storage space to add to the original underseat tool tray - just perfect for lightweight waterproofs, extra maps, or winter gloves."
Images from the R90S website