A superb and rare photo, made from the original
negative, of the great BMW R 90 S,
of 1974.
The first series of R90S sported a distinctive two
tone paintwork (Black/Smoke) called "TT silberrauch" or "TT
smoke silver" with adhesive gold pinstripes (no longer hand painted by the
factory; only the first series of R90S had these kind of pinstripes. Customer
complaints convinced BMW to turn back to hand painted pinstripes for later
years). Later variants (August 1974 on) were sold both in "Smoke Silver
TT" and "Daytona orange" (orange/silver with red pinstriping).
The R90S was an individual factory motorcycle – no two left the factory the same
due to the individual differences in each motorcycle's paint job. Look at two
identical machines from the same production run and you can see this difference
today, which makes restoration a subjective task. The R90S sported a small but
effective factory-fitted Bikini Fairing, which held four dial instruments
(speedometer, tachometer, clock and voltmeter). The first series R90S was only
equipped with a 238 watt alternator (All other "/6" machines had at
least a 280 watt alternator), which meant after market lighting or heated
handgrip accessories would be less effective on this bike. For this reason on
the third series the 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. Aftermarket fork gaitors are often fitted
to the bike but are not required due to the relative hardness of the fork
stanchions. Other critical engine differences are that 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 and
1000 cc series machines. Later 1977 to 1980 1000 cc machines sported 40 mm Bing CV carbs).
There are many, small differences on the three series of R90S. On the first
series, the brake discs are not drilled, and the handlebar switches are the
same of the "/5" series and the front axle diameter of the first
series is smaller than those of the second/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. On the road, the R90S was a capable solo or two-up sports machine. The
addition of either Krauser or BMW hard panniers and either a rear rack or over
the cylinder 'toaster racks' made the bike a capable tourer. Overall, the bike
can exceed over 380 km
(236 mi)
on a tank of fuel. Its performance is modest compared with modern K-series BMW
bikes producing more than 160 bhp (119 kW), but the 67 bhp
(50 kW) pushrod-twin engined bike ran the quarter mile in around
13.5 seconds and went from 0–60 mph (0–97 km/h) in just over
5.4 seconds. 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. Owner
maintenance is standard practice with these machines. Valve gear was adjusted
by simple locknut, and timing was taken care of by points (later replaced by
electronic ignition in many models). Most other maintenance tasks were easily
achieved due to easy access to most mechanicals. Maximum torque is delivered at
about 5500 rpm and redline is at 7200 rpm. Top speed is 190 km/h (120 mph) upright and 200 km/h (120 mph) on the tank.
The bike will run at 190 km/h
all day if required, but the relative fragility of the overhead valve gear is
something that needs to be considered when running the bike over the redline,
as it has no rev limiter as found on modern bikes. As the OHV engine pushrod
valvegear components were designed ‘off centre’ by four degrees to accommodate
future plans to expand the R series bikes to 1000 cc, this slight offset
produces additional tensions on the OHV gear at maximum revs that need to be
considered by owners who ride over the limit. As for brakes, two 230 mm drilled discs
were gripped by single ATE callipers, with a 200 mm drum on the back
wheel. The 1974 onwards model bikes make a distinctive noise under braking
thanks to the drilled discs. Overall braking performance bettered the Japanese
offerings of the time (especially in the wet), but were substandard to
contemporary Brembo systems (which were subsequently fitted to BMWs from the
"/7" series onwards). The front brake's cable activation system for
all BMW "/6" series bikes, including the R90s, is also different to
other brands, as the master cylinder is located on the top tube of the frame
and is activated by a cable from the lever to the cylinder. 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 disc brakes replacing rear drums until the advent
of the R100R Mystic models in the 1990s. 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
providing adequate illumination for legal speed touring at night. 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. The tires are narrow in comparison to
modern bikes. The 19 inch
front and 18 inch
rear combination are narrow, but adequate for most riding activities. One
advantage of such a narrow tire combination is good stability on dirt roads: A
downside is the effect that worn tires places on the frame – a head shake or
tank slapper can develop on worn tires that mimics the feeling of loose or poor
condition head bearings.
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 1000 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.
It is a superb and rare photo, and this is your rare
chance to own it! It reflects a very interesting and historic piece of
motorcycling and BMW history. The size is perfectly suited for framing as it is
large: ca. 8 x 12”
(ca. 20 x 30 cm).