The BMW R90S
Bike of the week
We've chosen this bike as it was a favourite bike of our boss back in the mists of time at the dawn of Wemoto in the late 1970s, early 1980s. In fact the company bought up a lot of old police BMW boxers for use by the fleet of London despatch riders back in the day. Sadly his old R90S was stolen in Brighton in the 1990s!
Superbike?...
So the BMW R90S was a 900cc sport bike which began production in 1973 overseen by designer Hans Muth. It was really designed to be a cool aspirational motorcycle, a new direction heading away from the somewhat staid, dull workhorse image which BMW had up until then. It was a 6” boxer engined motorcycle and began life with a supposed 'superbike' look but which was actually a rather dullish two tone smoke black/silver livery, a new duck tail, a bikini fairing and fitted panniers.
Fast...
The bike boasted a top speed of 124mph with a 67 bhp and could accelerate from 0-62 mph in 4.8 seconds. Max torque came at 5,500 rpm with the engine redlining at 7,200 rpm.
The R90S had a type 247 airhead pushrod overhead valve, air- cooled engine, with two valves per cylinder. It was a boxer unit with an engine based on the R75/5 but with a larger bore to take it all the way up to 898cc and a 5 speed gear box with shaft final drive.
Natty...
The R90S had a some natty little additional features like a redesigned seat with a useful little storage compartment for waterproofs and a built in tool tray with a complete tool kit, a pump, a first aid kit and a little groovy towel embroidered with the BMW logo. The colour scheme of smoke grey and silver underwhelmed the customers, so BMW brought out a new two tone Daytona orange version with hand painted red pinstripes to make it a bit more inspiring.
Sporty...
The R90S's bikini fairing contained two analogue instruments a clock and a voltmeter, its 238 watt alternator was later upgraded to 250 watts. The suspension was long travel telescopic forks with twin rear shocks with preload adjustable dampers. The R90S also had accelerator pump Del l'Orto carburettors and a sporty 9.5:1 compression ratio.
Brakes...
The motorcycle had tubed tyres and spoked alloy wheels with twin front brake discs and ATE callipers. This front brake system used an unusual system with a master cylinder on the top frame, tube activated by a cable from the front brake lever. This system was innovative, the theory of which was that it would protect the master cylinder if the bike was in a crash, but it was later ditched and BMW returned to a more traditional handlebar mounted Brembo master cylinder. The rear brake was a tried and tested 200mm drum brake.
Good things come in threes...
There were three production years of this motorcycle with various alterations and improvements made:
- 1973 - 1974 Original version - 6.058 units manufactured
- 1974 - 1975 This version had a stronger crankshaft and new main bearing - 6,413 units manufactured
- 1975 - 1976 Improved engine casings - 4,984 units manufactured
Capital punishment..
Anyone had or have one of these rare beasts or remember any of the BMW boxer twins either fondly or otherwise? Let us know at
[email protected]
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