BMW R90S

The high-speed BMW R90S set the motorcycle industry on its head
By Roland Brown
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BMW R90S
Photo by Roland Brown
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BMW R90S

Years produced: 1974-1976
Total production: 17,378
Claimed power: 67bhp @ 7,000rpm
Top speed: 125mph
Engine type: 900cc, two-valve, horizontally opposed twin
Weight: 215kg (474lb) wet
Price then: $3,430 (1974)
Price now: $3,500-$7,500

The speedometer shows a steady 80mph on the BMW R90S as the road ahead unwinds from a gentle curve. I’m sitting comfortably, leaning slightly forward to slightly raised handlebars, my chest and head protected from the wind by a neat half-fairing that also contains a clock and voltmeter.

The big orange fuel tank on this classic BMW motorcycle is full, giving the prospect of 200 miles of nonstop, high-speed riding. Below the tank I can see the engine’s cylinders sticking out either side, their gentle rustling almost drowned by a throaty twin-cylinder exhaust note. By modern standards the mechanical and exhaust sounds are loud, but they do nothing to mar the aristocratic air of the BMW R90S.

Nor does the bike’s stability as I bank through a series of gentle curves, suspension soaking up the bumps efficiently, the tall-geared engine feeling unburstable. Never mind its generous fuel range; this bike gives the impression that it would cruise at speed and in comfort forever.

Built for the long haul

However long BMW builds flat twins, it’s debatable whether there will be another to match the impact the BMW R90S made with its launch in 1974. The half-faired 90S, finished in a stylish smoked-color scheme (gray was the original color, with this bike’s orange following as an option a year later), may have been a sportster only by BMW’s traditionally restrained standards. But with a top speed a shade over 125mph, it was seriously quick by mid-Seventies standards.

The R90S was at its best traveling rapidly over long distances, but there was much more to this bike than sheer speed. Handsome, fine handling, comfortable, well equipped and very expensive, the R90S was arguably the best all-around superbike that money could buy.

The S and its unfaired relation, the R90/6, introduced at the same time, were derived more directly from the previous year’s R75 models. Enlarging the 745cc R75’s bore from 82 to 90mm while retaining the 70.6mm stroke gave a capacity of exactly 900cc. BMW also took the opportunity to make numerous engine mods, including strengthening the bottom end, plus fitting a revised gearshift mechanism and new alternator.

The R90S model differed from the humbler R90/6 by having higher compression (9.5:1 versus 9:1), and a pair of 38mm Dell’Orto carburetors with accelerator pumps in place of the basic model’s 32mm Bings. Those mods helped lift peak power output from the R90/6’s 60bhp to a claimed 67bhp at 7,000rpm — competitive with everything on two wheels except Kawasaki’s awesome 82bhp Z1.

In addition, the S model had a bigger, 6.4-gallon gas tank, twin 200mm front discs instead of just one, plus, of course, that handlebar-mounted fairing with its useful pair of white-faced gauges above the normal speedo and tach. The fairing, tank, front mudguard, side panels and the rear of the slightly stepped dual seat were all visually brought together by that classy paint scheme of subtly changing tones.

One drawback of the R90S paint scheme is that it is almost impossible to retouch, meaning that damaged bodywork must be replaced, rather than repaired, if the bike’s appearance is to be maintained. But BMW’s traditionally excellent standard of finish means that this unrestored R90S still looks remarkably good after 42,000 miles, with just the occasional minor blemish and a slight discoloration of the exhaust pipes.

On the road

It runs very well, too, after you’ve reached inside the fairing to the strangely placed ignition switch, then pressed the button to bring the boxer motor to life with its traditional side-to-side lurch. Despite its raised compression and big Dell’Ortos, the R90S was still as refined and well-behaved as any BMW.

Perhaps the most vivid sensation when riding the R90S now is just how similar the old bike feels to more recent boxers. The tuned S model has a little less low-rev torque than the 90/6 but is still very flexible, its docile power delivery and relaxed cruising ability feeling typically BMW. Even the sloppy gear change would be all too familiar to riders of relatively recent machines.

The R90S’s top speed of slightly over 125mph was impressive by mid-Seventies standards, but perhaps more important was the unmatched ease with which the BMW could sustain an easy high-speed cruise, thanks to its engine’s lack of annoying vibration and to the way the fairing diverted most of the wind from the rider. Aftermarket fairings were available that would do a similar job for other bikes, but no standard rival was as easy to ride fast as the Bavarian bahn stormer.

When you examine the spec sheet it’s no surprise that the elderly bike matches many of its more youthful descendants. Far from being much more powerful, the R100 model that BMW produced almost two decades later, in the early Nineties, had a lower 60bhp peak output. The manufacturer’s official 0-62mph (100km/h) figure put the R90S and 1993-model R100s dead level at 4.8 seconds, and the old warrior more than matched the later boxer on top speed.

Inevitably, the elderly BMW’s chassis has aged much less gracefully than its engine. The R90S shows its age particularly with its front brake, a combination of tiny calipers and drilled 260mm discs that require a firm squeeze of the lever to deliver much stopping power. This particular bike’s setup may have been slightly below par, but braking has never been the R90S’s strong point. Its original, solid 200mm rotors were quickly upgraded after a cool reception on the bike’s launch. At least the rear drum gave some welcome extra bite.

Handling and road holding were excellent by the standards of the day, thanks to a conventional blend of steel twin-down tube frame, leading-axle forks and twin-shock rear end. This bike’s spindly forks benefit from a brace, and its original shocks have long since been swapped for a pair of Konis. But the feel was much the same as ever: tall, stable, neutral, and fairly soft.

And if the elderly BMW feels a little wooden and unwieldy by modern standards, thanks partly to its narrow 19-inch front wheel, it’s worth remembering that the R90S was produced before the Japanese manufacturers had managed to make their big bikes handle at all. There’s none of the Kawasaki Z1’s loose feel at the handlebars, for example, even at straight-line speeds over 100mph.

In this respect, as in almost every other, the R90S has grown old very gracefully, indeed. Sure, its lack of a Paralever rear end means a certain amount of driveshaft reaction. Hard riding on bumpy surfaces finds the limits of the suspension, and under aggressive cornering on smooth roads this bike’s Metzeler tires give more than enough grip to get the engine’s cylinder heads scraping.

Reaching back

But the R90S matched its healthy power output with a respectable fueled-up weight of 474lb, which helped ensure that despite its shaft drive and gran turismo image there were few bikes that could stay with the BMW on the road. If proof were needed of the twin’s sporting potential, Reg Pridmore’s 1976 U.S. Superbike championship on a stock-looking boxer surely provided that.

More importantly, the R90S was — and still is — very capable of cruising comfortably at speeds well in excess of most countries’ limits. This bike was built long before most current grand prix riders were born, but the BMW belies its age with performance that hints at just how good it was when it first appeared back in the disco era. Reading old road tests gives an even better indication.

Among the most telling contemporary comments was the review that stated: “The R90S handles and stops almost as well as the best Italian sportster; is almost as fast as the fastest Japanese road burner; almost as uncomplicated as the good old British twin; and almost as smooth as the best multi. When it comes to comfort, and capability for traveling at maximum speed with minimum fatigue, the R90S is second to none.”

The tester concluded that while there were many bikes that did one thing superbly, the BMW was the only one that did everything very well. After riding the legendary R90S all these years later, that praise is easy to understand. MC 

Press reports

"Now, for hauling even faster and with a considerable amount of style, BMW has the R90S. More cubic inches. More class. Fantastic."
 — Cycle World, December 1973

"For the most part the engine will respond instantly, but the rider’s task is hampered by a throttle that is not quick enough for precise control."
Cycle World, December 1973

"The front brake on our Sport was mushy, not progressive, and provided little feedback to the rider."
Cycle Guide, November 1974

"There’s absolutely no doubt that the R90S is a remarkable motorcycle. It does or can be made to do, almost everything as well and possibly better than any other road machine you can buy."
 — Cycle, March 1974

"For a sport-touring machine, the 1975 R90S is a virtually flawless package."
Rider, Fall 1975

"There are times, as when going quickly over choppy road surfaces, when the BMW’s unsprung rear wheel masses get to be a bit more than its springs and shocks can control."
 — Cycle, January 1976

"There’s probably no better way to go from New York to San Francisco on a motorcycle than on an R90S."
Cycle, January 1977


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Post a comment below.

 

Russell_2
12/9/2011 1:16:24 PM
I had a silver smoke '74 R90S back in 1979. It was sold to me as having 25,000 miles. I was later to find it was 125,000 miles! I wouldn't have believed that had I not met an old friend with the same bike who had put on a little more than 100,000 miles in just two years. This bike really invited long distance riding. I would ride from Vancouver Island to the Oregon coast and back on a long weekend. I used to check gas mileage regularly and measured 50 mp(Imperial)g at 90mph average. 90mph seemed the most fuel-efficient speed and was the bottom end of the sweet spot which extended from 90-110 mph. 100 mph was the optimum speed for my bike - the quietest and smoothest and the suspension seemed to work best at that speed. I had the higher "touring" windshield and if I leaned forward two inches at 100mph helmet wind noise would disappear and the loudest sound was the tires on the road, followed by the wind in the spokes and then by the rockers clicking and finally by the exhaust, in that order! I would get lengthy "air" over the tops of road crests at that speed and could even land a little crossed up and the bike would sort itself beautifully on landing, I should never have sold it, but I did get 100,000 miles of pleasure on it.








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