Reviewed 

BMW R90S

Greatness is a label that’s easily applied, but accurately defining what makes someone or something great adds substance to the admiration. Recognized by many as the motorcycle that saved BMW motorcycles, Spandau‘s podium-topping favorite son had everything it needed to soar straight into legend. And more. Launched into a market where bravado increased annually, nineteen seventy-four’s R90S was a hand stitched leather glove across the face of its rivals – combining class, sass and considerable dash. Reliability? Every inch the cross-country steamer as BMW’s legendary R69S, with redefined levels of…everything. Performance? It’ll nip at the Desmo’s heels climbing passes, keep a Mach III in sight through the change up and pull the Z1 in top gear. Regarding the R90S’s most dramatic feature, it is said the deep black on 1974’s silver smoke R90S represented BMW’s foundational elegance, while its fogged silver depicted the motorcycle’s white-hot push into the future. Indeed!!         

This spot seems ideal to discuss some pre-R90S history, and the inspiration behind this review. My father introduced me to the brand at an early age, ironically explaining the wonders of the German twin as relating to the Japanese made Marusho 500 he’d bought. Probably just happy I was reading something, dad brought home some motorcycle magazines with BMW stuff for his eight-year old, who was never the same. By eighteen I was spinning miles on a black 750cc toaster, then an RS (twin and four) even a 500 slash-two – and that’s not counting the ones added by my family. Because it’s always the prettiest bike in any room, Neil’s smokey red 100S shrouded my interest in its 900cc predecessor, but contacts along the way helped fill that Dell’Orto shaped void. Even before the magic spun by Eng. Hans-Gunther von der Marwitz, marketing guru Bob Lutz or designer Hans Muth, without BMW’s 1963 investment in a new design there would be no 90S to celebrate. Well remembered by some factory workers I interviewed at the R1200R press launch in 2006, it was the motorcycle enthusiasts inside that Munich boardroom truly responsible for saving the fabled flat twin. Refreshments flowing freely in a lodge somewhere near the Austria border, my questions about the sporting 900 sparked a lively and engaging conversation with some of the engineers and test riders involved then. To them, passionately, the R90S was surely ‘the best of times’.                     

Chassis: Playing a large role in its character, the R90S frame is tall and narrow; measuring just 12″ across peg-to-peg. Draw a direct line from the design to Eng. von der Marwitz, who in the mid-1960s patterned it after Norton’s Featherbed, then the industry standard for handling and stability. Made in oval steel and baked in black enamel, the frame is cross-braced front and rear with a bolted on subframe and bearings in the swingarm pivot – half of which holds the driveshaft. As BMW did consecutively with every displacement increase, key strengthening points were made to the R90S in accordance to its boosted output and braking force. Looking to increase stability in 1973 the /5’s twinshock grew 50mm then carried over to 1974’s Slash-Six. Longer, stronger welded steering head plates work with a larger cross-member near the swingarm pivot/battery area, and (as some reports say) 1975-on for the double-wall top frame tube and 17mm (up from 14mm) front spindle. Raked to 28-degrees the leading axle, 36mm Fichtel & Sachs fork lost its gaiters and now straddles twin 260mm rotors pinched by adjustable ATE calipers. BMW’s 200mm drum is retained on the polished 18″ aluminum rear wheel, and an equally lovely 19″ front to match. Both feature BMW’s safely locking system.  
   

(Introduced late 1969, the Slash-Five frame (left, in B&W) was used across the entire /5 line. Among the very best available then, the made-for-BMW Fichtel & Sachs fork is a leading axle design. Made stronger for 900cc and disc brakes, BMW’s /6 frame is shown in Butler & Smith’s 1974 brochure) 

Engine: As the most traditional BMW component of a very nontraditional BMW motorcycle, changes were made inside and out to the opposed twin. Most everything I’ve read suggests the German 750 served as the Slash-Six’s starting point…but maybe not. Addressing the launch of Type M04 in 1969, BMW’s own technical publications state a 900cc twin was ready to debut then; and imagine the shock waves if it had. Covering R75/5 performance tuning here, reviewing some basics of Airhead construction gives considerable clarity to its on-road performance. For 1970, BMW’s new tunnel was both taller and wider than the /2 it replaced, but not by much. Now forged, the crankshaft rides on three plain bearings while the cam and pushrods hide underneath. Topside, the rear tunnel seals the airbox/breather and electric starter, positioned over the ring gear. Under the front cover bottom to top is the ignition advance/points, crank drive alternator and camshaft drive connected by duplex chain. Important Airhead fact: from 500cc to the biggest 980cc the same 70.6mm of stroke is used, giving each revision its own unique character.                            

(1974’s /6 cutaway shows starter/ring-gear engagement. Now with five-speeds. recalls for the transmission and kick starter were issued in 1974. Black cylinders and 38mm PHM Dell’Ortos define the sports 90S, plus motorcycling’s all time coolest engine badge. Twice the weight of cast iron, tungsten steel plugs were machined into the /6’s sized-down crank flywheel to restore balance. Forged crankshaft and rods run in plain bearings/high pressure oiling.) 

In an effort to boost output while keeping the assembly mechanically understressed, BMW’s distinctive engine tunnel was somewhat redone for the /6 series. In racing conditions, some Slash-fives cracked the casting around the main bearing mount, so the case was strengthened with a revised front engine plate and vented cover. Tilting to install the R90’s forged crank into the rear main bearing, the front flywheel wouldn’t pass through the smaller, stronger front port, so it was resized and heavy tungsten balance plugs machined in to restore balance. Established on the /5, the 900’s oiling comes from a geared pump driven by the standard ‘308’ camshaft, with larger (42 inlet/40mm exhaust) valves and needle bearing rocker pivots. BMW attributes the Sport’s extra seven-horsepower (67 compared to 60) over the R90/6 to its domed 9.5:1 pistons and 38mm Dell’Orto pumpers. Only the 90S received black heat dissipating paint to its cylinders. Due mainly to those huge 90mm pistons increased crankcase pressure sent more Castrol 20/50 through airbox/breather than before, so levels are checked often on models living at high RPM.         

“The low, narrow bars hunker you down where the small faring deflects the wind, and the ride, seating and fuel capacity lets you stay at it for hours. Roads streaming under the flashing spokes, the exhaust is a civilized basso rumble. Power to spare and reliability unquestioned, only the omnipresent possibility of red lights twinkling in the mirrors will keep you from letting the R90S do what it does best – which is devour miles in giant bites”. 

 (Cycle Magazine – January 1976)

Market share/impact: Start searching R90S on your favorite uplink and they’ll be no shortage of material. Many share a common theme, showing the R90S arriving just in time to rescue a rudderless motorcycle division that both press and public viewed with disdain. Yet the numbers say both the 750/5’s speed and sales figures combine with period press reports to expose that version of history as romantic nonsense. There wasn’t a better production motorcycle available in 1970 than BMW’s 750cc flagship, and just about every road test published said as much. Given that, even the dressed up Toaster couldn’t be expected to face the coming horsepower/image onslaught, but as previously noted, the Germans had 900cc’s waiting. Long an editorial point, BMW and Europe’s other surviving builders weren’t just experienced, but savvy. By 1974 Guzzi and Laverda had 1000cc and Ducati’s new Desmo measured 900cc, yet all of them (and especially BMW) had the foresight to build base models with most or all of the mechanical updates lavished upon their sporting flagships. Making a point; if BMW’s traditional twin had lost all appeal, why make them? BMW sold more seven-fifties between 1970-to-1973 than the R90S’s three-year production, and more R90/6 models during the same period. Its high retail price played a role in those figures, but the R90S didn’t up sell BMW’s traditional market, it expanded it.                                

Pondering it for decades, I’ve adopted the belief that several key factors contributed to the R90S’s considerable lore. Plainly, and like a few others to follow from BMW, it’s clever visual presentation defines it – attracting riders and non-riders alike. “It was important the R90S have a face,” said designer Han Muth. “To that effect, it was intended to wrap the rider in a fighter pilot atmosphere with a fully appointed, comfortable cockpit filled with clocks.” Once having to hide his motorcycle drawings from his bosses on BMW’s auto side, Muth’s vision of the company flagship landed the 90S in uncharted territory like fashion magazines and Playboy, polishing the page with an exotic, elegant flair like nothing else on two wheels…or four. At least, American cars made in 1974, and being capable of ripping off 13-flat quarters (even with tall 3.00:1 gearing) the 90S was faster than Detroit’s fastest-ever musclecar. By 1975, long time owners and first timers arrived together with fistfuls of dollars, sold through BMW’s expanding dealer network and a growing reputation for quality. Some period scribes predicted poor sales due to its $3500.00 retail (the cost of two new CB750s) but there were no leftovers. Perhaps more could have been sold, but Spandau‘s struggle to meet demand was well publicized. Promising exclusivity, BMW’s lavish R90S was expensive to purchase because it was expensive to build. The majority done by hand.                              

(Built by BMW France, by then a division of BMW Munich, legendary German racer (and Metzeler tire technician) Helmut Dähne works the King’s BMW 980cc around the Le Mans Bugatti Circuit at the 1975 Bol D’Or 24 Hour Endurance race. Dähne and his partner René Guili finished ahead of everything…except three Z-1 powered Kawasaki endurance racing specials. Amazingly stock mechanically, the pair made 661 ‘tours’ totaling 1,818 miles.)

Racing: Already a chart-topper, the R90S’s racing success cemented forever its status in motorcycle history. Filled with courage and confidence, the story of US Importer Butler & Smith’s 1976 championship campaign (with riders Steve McLaughlin, Garry Fischer and first AMA Superbike champion Reg Pridmore) can be found many places online, so there’s little need to cover it here. Far less has been told, at least in the US, about BMW’s efforts elsewhere, but 1975’s Bol d’Or 24hr Endurance was memorable for the racing 90S. Like Udo Gietl’s AMA warriors, the King’s BMW was taken out to 980cc (94 x 70.6mm) but retained its twinshock swingarm. “As I remember it, KINGS was a sponsor,” says Helmut Dähne, who continues as a keynote speaker at motorcycle events in Europe. “I don’t know anything about them – I only rode the bike.” Many hours later, not much more has been uncovered but it was learned that BMW France was an extension of BMW-Munich, put in place to promote the brand accordingly and the King’s 980cc was part of that. “There was not many changes to the engine,” Helmut replied when I pressed for tuning specifications. “High compression 94mm pistons, the 336-degree Sports camshaft (available through BMW’s special parts catalog) large Dell’Orto PHM carbs, race exhaust and Lockheed brakes. That’s about all. I do seem to remember the the fairings were made by the French. The seat the same as the year before, so possibly it was the same bike”. Like the IOM (which Dähne won in 1976) France’s Bol d’Or was a top tier event attracting each factory’s very best. To place fourth behind the dominant Kawasaki’s in this brutal atmosphere says more about the 90S than any advert ever could. Just for reference the event manifesto shows the BMW team of Pridmore and Fisher also entered, dropping out after 167 laps. 
       

(AI embellished B&W drawing of the King’s BMW 980cc. Could it still exist, somewhere? More digital whizzing applied to Dähne’s hard-right at Le Mans. Surely among the most beautiful racers ever. On the road in the USA: 300k plus mile Hienrich/Fallert/Avon 90S shows a different kind of endurance) 

Perhaps the greatest attribute of BMW’s R90S is its lasting impact. If you like attention this is the bike for you, and it isn’t just strangers approaching at fill ups. And it is there, in the Year of our Lord 2026, where the majority will spot the resplendent sports roadster, lashed with luggage and properly splattered from a tri-state trifecta. In Cycle’s 1974 new model preview, the 90S was portrayed as a gem-encrusted exotic; purchased mainly by the affluent to pose in marble parlors. Given the cost that view is understandable, but the sheer number of 900 Sport’s that reamain in service is considerable – due in large part to the industry’s best parts and service network. Aftermarket performance mods will transform the German twin into more of a dedicated sports/racer, but even in stock form BMW’s tuned 900 is more than capable. Adored by owners for its steady, forgiving composure, rain or shine. Have I mentioned the seating or adjustable pegs? Am I remiss in mentioning its well stocked tools, underseat bins, security lock, tire pump or clock? Even an embossed BMW towel. It’s bikini sport motif copied endlessly, the 90S has for years been regarded a solid, if considerable investment. Even in this butter soft market, but cherished by many for many different reasons. Everything totaled, it’s hard to argue the R90S didn’t save the famous German firm, but the same has been written about BMW’s R100 RS, 80 GS, and K-four. A classic case of apples and Daytona Orange, one fact that cannot be dismissed is the 90S’ leading role in bringing the European open-classer out from the Big Four’s shadow; combining levels of performance and style not found anywhere else. Both highly decorated and underrated, BMW’s R90S reminds us that some motorcycles are remembered, others are impossible to forget. Nolan Woodbury                             

A very warm thank you to Brother Bob Hardacker, whose R90S’s (more than one) appear prominently in this review. Also brotherman Billy Ross for the intros and technical stuff, Jim Robinson, my son Alex and blood-kin Neil, Nick and Nathan. In memory of my BMW spirit guide, Marty Cohen. RIP. NW