BMW R90s is the first bike in the world to have full body fairings. The fairing itself functions as an aerodynamic channel. This functional body style is an innovation for the world of motorcycles and has inspired the majority of sportsbikes today.
This R90S is fitted with a type 247 engine, otherwise known as an airhead. The engine is an OHV, two valve per cylinder, air-cooled flat-twin, or boxer engine (Following BMW's boxer tradition). The R90S weighs 215 kg (470 lb) and has a five-speed gearbox with a shaft final drive. The R90S was introduced with the new BMW "/6" series along with another new model the R90/6. The R90S and R90/6 were introduced in 1973 along with the revision of the already existing 600 cc and 750 cc bikes that were now called R60/6 and R75/6. The earlier R50/5 of the "/5" series was dropped.
There were three series of R90S:
- model year 1974: September 1973 to August 1974 (6,058 units)
- model year 1975: June 1974 to September 1975 (6,413 units)
- model year 1976: August 1975 to June 1976 (4,984 units)
The first series of R90S sported a distinctive two tone paintwork (Black/Smoke) called "TT silberrauch" or "TT smoke silver" with adhesive gold pinstripes, which later changed to hand painted pinstripes.
The R90S sported a small but effective factory-fitted Bikini Fairing, which held two dial instruments (clock and voltmeter) in addition to the normal instrument binnacle's speedometer and tachometer. The first series R90S was only equipped with a 238 watt alternator, while the other "/6" machines had at least a 280 watt alternator). The third series R90S alternator was upgraded to 250 watt.
For most of the 20th century BMW earned a reputation for building reliable, if somewhat stodgy, touring motorcycles. All that changed in 1974 when BMW introduced its first superbike: the R90S. Higher compression pistons (9.5:1), 38mm Dell'Orto accelerator-pump carbs and twin disc brakes distinguished the S from the more-pedestrian Beemers-but what really set the R90S apart was its looks. The S featured a sleek seat with a metal ducktail, a curvaceous bikini fairing and striking two-tone Silver Smoke paint.
The bike's visual design was overseen by Hans Muth, who was asked by BMW to create a machine with a unique presence far removed from the staid image offered by previous BMW offerings such as the 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 added a second underseat storage space to add to the original underseat tool tray suitable for lightweight waterproofs, maps, or gloves.
The bike was originally equipped with a phenolic disc and spring engine crankcase breather, which was superseded by a reed valve design on the "/7" series. An original R90S (as with many "/5" and "/6" machines so fitted) makes a 'plopping' noise at idle as the crankcase breather manually opens and closes: later reed type breathers retrofitted to earlier bikes removed this feature.
A H4 headlight provided illumination. The switchgear was upgraded in 1975 from the previous "/5" system. The indicator switch now operated on the vertical plane, rather than the horizontal one used by most other manufacturers. As of 2009, both BMW and Harleys continue with different switchgear to manufacturers in this regard. The ignition key is placed on the left headlight mounting point. The steering lock is mounted in the steering headstock.
Quite surprising is the compactness and narrowness when sat upon the Beemer, what looks like a very big bike as you approach it becomes nothing more than a powerful middleweight once sat upon it. The bars are hardly wider than your shoulders and the footrests, off set to match the cylinder spacing, incredibly close together, around five inches further in than anything the Japanese have to offer. Even the large capacity tank isn’t in any way bulky, achieving its five and a quarter gallon capacity with length and height rather than width. This instantly endears itself to the rider as you sit fully on the centre line of the machine making the bike feel balanced and not at all the capacity it is. At low speed the bike is so easy to keep upright there is hardly a need for that comforting foot down, U turns can be performed with consummate ease, feet up all the way, while sitting at junctions and traffic lights can often be done the same way, The engine configuration helping no end in this aspect with very little weight above mid shin height.
From 1973 to 1976, 17,455 R90S models were sold. The R90S became the R100S in 1977, which maintained the R90S bikini fairing, but ran the full 1,000 cc engine, 40 mm Bing CV carbs, and altered paintwork. The mantle of the lead BMW factory twin was passed to the R100RS, which by now sported a full fairing (note: 'specials' such as the 4V Krauser and Fallert BMW's are not compared in this article). Other factory variants such as the R100CS were also produced in later years, sporting spoked wheels and black-painted square valve covers; as a sort of 'licht' derivative that was available only in black bodywork.