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|Engine||898 cc Four-stroke, two-cylinder, horizontally opposed "Boxer", air-cooled|
|Bore / stroke||90 × 70.6 mm (3.5 × 2.78 in)|
|Top speed||200 km/h (120 mph)|
|Power||67 hp (50 kW)|
|Torque||76 N·m (56 lbf·ft)|
|Transmission||5-speed, shaft drive|
|Brakes||Front: dual 260 mm discs
Rear: 200 mm drum
|Wheelbase||1,465 mm (57.7 in)|
|Dimensions||L 2,180 mm (86 in)
W 740 mm (29 in)
H 1,210 mm (48 in)
|Seat height||820 mm (32 in)|
|Weight||215 kg (474 lb) (wet)|
|Fuel capacity||24 l (5.3 imp gal; 6.3 US gal)|
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. The R90S weighs 215 kg (474 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.
The bike also possessed an adjustable hydraulic steering damper activated via a knob located on the steering head. Suspension is by telescopic forks at the front and twin shocks at the rear. The rear dampers were adjustable for preload, which is the only suspension adjustment available. The R90S came equipped with standard 38 mm Dell'Orto 'pumper' carburetors, differing from the previous 26 mm Bing slide carbs or 32 mm Bing CV carbs of the standard "/6" and "/7" 800 cc, 900 cc and 1000 cc series machines. Later 1977 to 1980 1000 cc machines sported 40 mm Bing CV carbs. The R90S differed from the R90/6 by sporting a 9.5:1 compression (R90/6 was 9:1) and 38 mm DellOrto round slide carbs instead of the 32 mm Bing CV carb on the R90/6.
There are numerous differences on the three R90S series. On the first series the brake discs were not drilled and the handlebar switches are the old "/5" series style. The first series was also still equipped with a "/5" series kick start lever and the front axle diameter is smaller than that of the second and third series.
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.
Maximum torque is delivered at 5,500 rpm and the engine redline is 7,200 rpm. The 67 bhp (50 kW) pushrod-twin engined bike could reach a top speed of 124 mph (200 km/h), ran the quarter mile in around 13.5 seconds and went from 0–62 mph (0–100 km/h) in 4.8 seconds.
Two 230 mm drilled discs were gripped by pivot-pin ATE callipers, with a 200 mm drum on the rear wheel. The front brake's cable activation system for all BMW "/6" series bikes, including the R90s, is also unique. The master cylinder is located on the top tube of the frame below the tank with a standard brake fluid reservoir and is activated by a cable from the handle bar brake lever. The argument was that this system offered greater protection for the master cylinder in the event of a crash. Later "/7" machines reverted to handlebar mounted Brembo master cylinders, with a single disc brake replacing the rear drum.
The R90S came standard with a full toolkit, a hand pump, a first-aid kit and even a small hand towel with an embroidered BMW logo.
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[update], 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.
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.
A later example of the R259 oilhead BMW, the R850/1100R, sported a similar two-tone smoke grey paint scheme in homage to the original BMW 'superbike' color scheme.
Two R90S bikes placed first and second at the very first AMA Superbike race at Daytona in 1976. On the first place bike was Steve McLauglin and on the second was Reggie Pridmore. The first place bike is now in the BMW Mobil Tradition Collection.
- "BMW R90S Specifications". BMbikes. Retrieved 12 August 2009.
- "Media Guide 2007" (PDF). AMA Superbike Championship. p. 302. Retrieved 2007-09-20.[dead link]
- Roland Brown (Premier Issue). "BMW R90S: Bahn Storm". Motorcycle Classics. Retrieved 2009-08-24.
- "R90S Specifications". bmbikes. Archived from the original on 13 December 2010. Retrieved 21 November 2010.
- Motorcycle Classics, Jan/Feb. 2010 p.18
Media related to BMW R90 at Wikimedia Commons