Motorworld’s newspaper №54
In 1940, the Wehrmacht’s Ordering Department announced a tender for developing a heavy motorcycle with a sidecar, with 3×2 axle configuration, capable of towing a light artillery gun or a munition trailer. By the end of the year, the Bayerische Motoren Werke, AG developed one of the best military motorcycles ever, the BMW R75.
Clearly, all test runs in general, and especially the International Six Days Trial, played a very important role in the development of German military motorcycles. This had a particularly strong impact on the preparation of numerous motorcycle bodies, which became the vanguard of the German armored divisions.
Before the beginning of World War II, Germany paid a lot of attention to motorcycles with sidecars, this was clearly visible in the number of participants in the International competitions, among which the most Germans were on motorcycles with sidecars. Later on, the German advocacy openly admitted that it was these sports competitions that helped identify design flaws and train top-class drivers using the harsh conditions of the competition.
Of course, the military operations were very different from the competition: drivers had to pass thousands of kilometers within months, often unable to make major repairs. In addition, the terrain was much harsher than in the trials, and the fact that no one specifically selected these motorcycles, as the best of the produced, had an impact on further requirements for these ‘cross-country vehicles’.
In the mid-1930s, bikes with sidecar wheel drive began to appear in Belgium (FN M12a SM), France (Gnome-Rhone AXII), England (Norton Big Four), and even Japan (Rikuo Type 97). These motorcycles with the 3×2 axle configuration showed the perfect results, but the German war machine was not in a hurry to pick. The Wehrmacht wanted the best off-road motorcycle for itself.
FN M12a SM located at the motorcycle museum “Motorworld by V.Sheyanov”
Gnome Rhone AXII located at the motorcycle museum “Motorworld by V.Sheyanov”
Norton Big Four located at the motorcycle museum “Motorworld by V.Sheyanov”
Rikuo Type 97 located at the motorcycle museum “Motorworld by V.Sheyanov”
By the autumn of 1937, the Wehrmacht’s Supreme Command came up with the requirements for a new off-road motorcycle, and two of Germany’s largest motorcycle manufacturers, BMW and Zündapp, undertook the order. The final prototypes were similar both externally and constructively, but today we will only talk in detail about the BMW R75, and the Zündapp KS750 will be left for later.
The ancestor of the R75 was the R12 model, introduced in 1935, which was distinguished by a telescopic front fork with hydraulic shock absorbers. The powerful 746 cc engine, 4-speed gearbox, and shaft drive made the machine fast and reliable, but the short distance between the wheel and wing caused many problems for German motorcyclists on the Eastern Front.
BMW R12 located at the motorcycle museum “Motorworld by V.Sheyanov”
The engine was something like the flathead engine of the R71 model. The gasoline four-stroke, two-cylinder ‘square’ engine (bore and stroke = 78 mm) with a working volume of 745 cc was mounted across the frame, but in contrast to its more peaceful ‘ancestor’, the new engine has become an OHV. For ease of maintenance, the rocker arm of each valve had a separate cover. The new power unit, designed not so much for maximum power as for long service life, developed 26 hp at 4400 rpm.
The motorcycle had a kickstarter. The magneto used in the ignition system with the mechanism of automatic adjustment of the ignition timing made the whole system reliable, as evidenced by the spark plugs, which functioned flawlessly for more than 12 thousand kilometers without cleaning or replacement. The magneto, also used on the Zundapp KS600 and BMW R71, was supplied by two manufacturers: Noris ZGA2 and Bosch FJ2 R134. The copy from Motorworld’s collection has the magneto Noris, which proved to be excellent.
The magneto and camshaft were driven by a gear system. The engine turned out to be very reliable, did not overheat at low speeds, and worked perfectly in the cold, thanks to two carburetors Graetzin Sa 24. Good cross-country ability in overcoming water obstacles provided rubber caps on mixing chambers of carburetors and special tips for spark plugs.
Let’s make it clear, there were several modifications of the motorcycle R75 that changed throughout the production. The engine parts, suspension, and even coloring were subject to changes. Officially, the first version had no name, but there were such nicknames as “Europe” and “Siberia”, the most famous of later versions was named “Sahara”.
Valve caps also changed, and in the case of “Sahara”, they were no longer painted in the color of the motorcycle. A slight ribbing has been added for better cooling of the cylinders
The first versions of the motorcycle were painted dark gray (aka Feldgrau color). The “Sahara” was one of the first to get yellow-sand color, and a little later, in February 1943, ‘sand camouflage’ received all fighting vehicles of the Wehrmacht, except for those that served on the Eastern Front.
On the first versions of R75, the filtering element was located under the gas tank, on a standard for BMW spot, in the casting of the body of the gearbox. The decision to change its location was affected by the sands of African deserts and the mud of Russian roads, which clogged the air filter too quickly. On “Sahara” the filter took the place of a glove box on top of the gas tank and was covered with a lid, very similar in shape to a German helmet. The design and layout of the air filter, with a device to provide suction during engine start-up, made the launch less problematic.
The exhaust system was also with a twist. The exhaust line from the cylinders came to a small receiver located in front of the engine crankcase, and only then went to the back of the bike, to the silencer. This part of the silencer was covered with a perforated sheet of iron to protect the rear passenger’s legs from burns.
In 1943, the Germans changed the exhaust system of “Siberia”. Now the exhaust fumes passed through a heat exchanger, warm air from which was used to heat the legs and hands of the driver, as well as heating the bottom of the sidecar.
The engine and gearbox were mounted in one unit. The clutch in the BMW R75 wasn’t any special, it was dry, single disc. But the four-speed gearbox with reverse gear and demultiplier was a real work of art. The gear was changed either with the left foot or with an internal lever mounted on the right side of the gas tank. The sidecar wheel-drive was controlled only by a hand lever. The outside lever controlled the demultiplier.
The torque from the gearbox was transmitted with a help of a cardan shaft to the differential. Through the differential, the torque was transferred to the rear wheel of the motorcycle and the wheel of the sidecar. Thanks to the differential, the bike went straight and didn’t go off its trajectory even at high speeds. If the bike got stuck in the mud, so that one wheel spins freely, you could turn on the differential lock, which greatly increases the performance of the bike. The lever to activate the differential lock was located under the gas tank on the right side.
To the gear ratio, received by bevel and root gears of the differential was added an additional gear ratio, received in the transmission of the rear wheel and wheel of the sidecar by two additional spur gears. This was similar to the transmission of heavy trucks of those years.
The wheel of the sidecar had a torsion suspension while the sidecar itself had leaf springs. The MG 34 or MG 42 machine guns were installed on the front part of the sidecar. If necessary, the sidecar could be detached.
The spatial frame, built of pipes and stamped parts, was strong and could withstand high loads and difficulties of the battlefields.
The seats on the R75 were supplied by the well-known company Drilastic. The “Sahara” had the changed shape of the seats, differed from the first versions.
“Sahara” is a heavy motorcycle, much heavier than its contemporaries, which according to the traffic rules are limited to a weight of 350 kg.
The R75 weighs 420 kg and it goes very smoothly, despite the unsprung rear wheel. The R75 is easy to handle, thanks to the wide handlebars. The low seat allows you to reach the ground with your feet, especially with the left one. And this is very helpful in dangerous situations on the slopes, where the motorcycle could tip over on a slippery forest road.
The BMW R75 is easy to control, thanks to the wide handlebars and the low seat allows you to reach the ground with your feet.
All controls are modern and in place. The ignition starts by turning the toggle switch, without keys, which are so easy to lose in wartime!
The drive of the rear wheel and the wheel of the sidecar are so reliable that you can drag anything until the wheels get buried in the sand or mud gets stuck between the front wheel and the fender.
The BMW R75 is undoubtedly a technical masterpiece. The drive of the rear wheel and the wheel of the sidecar are so reliable that you can drag anything until the wheels get buried in the sand or mud gets stuck between the front wheel and the fender.
The hydraulic brake works very well! It stops the bike no worse than modern ones if everything is correctly maintained, of course. However, the maintenance of the brakes is also a challenge. As well as a ride on a solo R-75 – to detach a sidecar you have to sweat a lot!
Still, despite all the shortcomings, the BMW R75 is a central part of the “Motorworld by V. Sheyanov” collection. Vyacheslav set himself the goal to collect under one roof the best motorcycles of the Golden Age of motorcycling, which peaked in the 30s-40s of the last century. The museum’s collection contains over 100 exhibits, each of which is lovingly maintained and jealously guarded. But most importantly, all the exhibits are ‘alive’ and take part in small test-drives alternately, which are held in the fields and forests of the Samara region.
The front suspension is a telescopic fork with hydraulic damping. The first versions of the bike used metal shields that protected the moving parts of the shock absorber, but dirt and sand very quickly clogged in the slots, thus moving parts quickly came into disrepair. In the case of “Sahara”, this problem was solved by installing rubber dust collars, which reliably protected the shock absorbers.
At least that was the case on paper, but in reality, when you start to look at war pictures, you are surprised at the variety that was found on the battlefields: versions with a ‘helmet’-filter and metal shields, with glove box on the gas tank or with the valve caps of the old model.
Spokes used on R75 were reinforced to withstand high loads. All three wheels are interchangeable, the spare wheel was attached to the trunk lid of the sidecar. The tire size (4.5 x 16 inches) was unified with the Volkswagen Typ 82 (Kübelwagen).
Unrepairable motorcycles of various brands are dumped along the road somewhere on the coast of France. Motorcycle with sidecar – BMW R75.
All three wheels had drum brakes, but the front brake was driven by a cable and the rear brakes were hydraulic. The principle of operation has not changed since then: the driver presses the pedal on the R75 and it drives the main brake cylinder, which is in the casting of the body of the gearbox. The cylinder moves the brake fluid, which comes through the tubes to the rear wheels and ejected pistons’ brake cylinders.
Thanks to the high arches, it was possible to install chains on the wheels, which further increased the passability of the motorcycle. A part of the rear wheel arch tilts down to make it easier to change the wheel. In the “Sahara” version, the arches are made narrower and are located further away from the wheel than the first R75. Like any other off-road vehicle, with the help of the crew, the BMW R75 could overcome almost any off-road obstacles.
The fuel tank of the R75 with the volume of 24 liters provided a power reserve of 350 km, which corresponds to the consumption of 7L/100km on the track. To increase its power reserve, gasoline canisters with additional fuel were attached to the sidecar.
Today, gasoline cans are an integral part of our life, almost every motorist has such cans in the trunk, and for experienced motorists, it is an obligatory attribute of equipment.
During World War II, the Allies called a canister of fuel ‘Jerrycan’. The word ‘Jerry’ is a part of the military slang of English-speaking allies, which meant ‘Germans’).
The three handles on the ‘Jerrycan’ were not made by chance, but to meet the Wehrmacht specifications, which required the soldier to carry two full cans or four empty ones.
The motorcycle could carry a trailer weighing up to 450 kg. It could also be a 37 mm PaK-35/36 anti-tank gun and 81 mm s.Gr.W.34 mortar. According to some reports, the R75 could carry up to 8 (!) trailers coupled to each other.
Although the BMW R75 could be compared in terms of cross-country ability with the new SUV Jeep, but only with a very experienced rider. This qualification made R75’s operation even more difficult. In general, the R75 – one of the most advanced motorcycles of the Second World War, but perfection has its own price, in this case, the price was too high. The motorcycle costs the Wehrmacht the same amount as 3 Kübelwagen. Such expenses during the war were unacceptable, and in 1944 production was shut down. In total, 16,500 BMW R75 motorcycles were produced.
All fans of German motorcycles simply have to visit the motorcycle museum “Motorworld by V. Sheyanov”, where the perfectly restored BMW R75 “Sahara” is now located.
|Manufacturer||Bayerische Motoren Werke, AG, Munich (Germany)|
|Years of manufacture||1940 – 1944|
|Quantity produced, units||16 510|
|Price||1 595 RМ|
|Today’s value||10 309, 6 $|
|ENGINE AND TRANSMISSION|
|Type||twin-cylinder, OHV, with horizontally opposed cylinders, 4-stroke type|
|Engine capacity, cc||746|
|Bore and stroke, mm||78 х 78|
|Engine rating||26 h.p. at 4000 rpm|
|Sparking||Magneto generator, left-side kickstarter arrangement|
|Carburetor||2 units: Graetzin Sa 24 / 1 type and Sa 24|
|Clutch||Single dry plate|
|Transmission||4-speed + reverse gear|
|FRAME AND WHEELBASE|
|Frame type||Tubular welded|
|Brakes||Drum type with hydraulic drive, including the sidecar wheel|
|Wheel size||4,50 х 16 (3 wheels)|
|Ground clearance, mm||
|Seat height, mm||
|Gas tank size, l||
|Maximum speed, km/h||