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Motorcycle Investor mag

BMW R5

(by Ian Falloon, Mar 2022)

Falloon on one of BMW's foundation stones

Sometimes a motorcycle comes along that initiates an engineering and performance benchmark exemplifying an era, and during the 1930s this was arguably the BMW R5.

Circumstances at the time undoubtedly contributed to R5’s supremacy. While the British motorcycle industry struggled to survive during the Depression, in Germany the Nazis saw technological domination, particularly of motor sport, as one of the most effective sources of international propaganda.

While motorcycle racing wasn't as strong a propaganda tool as Grand Prix car racing, motorcycling was still a popular activity during that depressed decade. And as it was an industry almost totally dominated by British manufacturers here was an avenue the Germans could make their mark.

With the German government providing the necessary funds, BMW was able to make its first purpose built racing engine, the 500cc Kompressor, as well as develop a new range of street bikes. The first of these was the 500cc R5 of 1936, and it represented a significant breakthrough for BMW.

Central to the R5 was a new flat-twin engine with two chain-driven camshafts mounted above and to each side of the crankshaft allowing short pushrods. The timing chain also drove the Bosch generator on top of the crankcase, with the ignition coil and distributor positioned inside the front cover. The included valve angle was reduced to 80-degrees, the rocker arms pivoting in needle roller bearings, with double hairpin valve springs to provide safety at higher rpm.

The crankcase a one-piece tunnel type, with the crankshaft inserted from the front, a design that would characterize BMW flat twins for decades to come.

With twin 22mm Amal carburettors, ironically built in Germany under license, the 68 x 68 mm engine produced 24 horsepower at 5800rpm. This may not sound particularly impressive by today’s standards but it was enough to provide the R5 with considerably more performance than its 33 horsepower 750 cc R17 predecessor.

The main reason was the tubular-steel frame. Previous BMW motorcycles featured an archaic and heavy pressed-steel frame but the R5’s electrically-arc and gas welded (a process termed Arcatron) tubular-steel duplex frame was similar in design to that of the 500 Kompressor. It featured the same exotic combination of round and oval section tubing, selected according to the load expected.

Not only did the duplex tubular welded steel frame impart a more modern appearance but the unladen weight of the R5 was a svelte 165 kilograms compared to the R17’s hefty 183 kilograms.

In many other respects the R5 was also more modern than the earlier R17. A foot pedal on the left, as well as a right-side hand lever, now controlled the four-speed gearbox. As this positive stop gearshift design originated with Harold Willis’ 1928 Velocette it demonstrated BMW’s openness to incorporating new ideas, even foreign.

While the R17 may have pioneered the telescopic front fork, the R5 went a step further, incorporating an external damping adjustment. The rest of the running gear was standard BMW for the period, with 19-inch wheels and 200mm drum brakes, front and rear.

It was only the rigid rear end that limited the ride quality but this was compensated through a softly-sprung Pagusa rubber seat. The works racing bikes were fitted with plunger rear suspension in 1937 and this was subsequently adopted on the R51 from 1938.

The R5 provided exceptional sporting performance for the mid-to late 1930s. The top speed was around 140km/h and many enthusiasts rated the handling of the rigid-frame R5 superior to the later R51.

One of the standout machines of the decade, the R5 was a milestone in BMW motorcycle history. The R5 finally challenged the British in performance and handling and provided the basis for BMW twins for the next twenty years.