BMW R32
With Ian Falloon
Although BMW’s origins go back to 1913, when Karl Rapp established an aircraft engine factory in Munich, it wasn’t until a decade later that they produced their first motorcycle. Since that time, BMW has produced singles, twins, triples, fours, and sixes, but the enduring layout has been the boxer twin with shaft final drive.
This has become the trademark that defines the BMW motorcycle and it all began 100 years ago, in 1923 with the R32. The R32 evolved from BMW’s existing M2 B15 (2 for two cylinders and B for boxer) but as the rear cylinder tended to overheat on the M2 B15-powered Victoria and Helios, designer Max Friz decided to mount the engine transversely and adding a shaft final drive, and Friz had the drawings completed by December 1922.
Although the 1919 English Sopwith ABC motorcycle also featured a transverse twin-cylinder engine (without shaft drive), Friz claimed he was unaware of the ABC at the time. ABC’s designer Granville Bradshaw later accused BMW of copying the ABC, but there were too many detail differences for this to be substantiated.
The R32 68 x 68mm side-valve engine had a low 5:1 compression ratio and with a single 22 mm BMW Special carburettor produced a moderate 8.5 horsepower at 3200 rpm. This was slightly more than the M2 B15, but while the power output didn’t set the world alight, the R32’s design and execution was ground breaking.
Concentrating on reliability and ease of maintenance, the engine, including the valve timing system, was fully encased. Due to the shaft final drive and inline crankshaft there were no chains requiring adjustment so compared to other 500s the R32 was revolutionary. A hand lever operated the three-speed grease-filled gearbox, and the ignition was by a magneto generator via a rather complicated set of handlebar controls.
Friz installed this engine in a closed twin-loop tubular steel frame, with the fuel tank underneath the upper frame tubes. The frame was brazed and sleeved, but as the workers lacked experience in brazing, fractures on the solder joints were a problem until the introduction of pressed steel frames in 1929.
The front suspension consisted of a short swinging fork with a cantilever plate spring beneath the steering stem. The rigid frame meant the driveshaft didn’t require a universal joint, with a rubber disc a sufficient shock absorber, Initially the only brake was a rear wheel block type operated by the rider’s heel, but by 1925, a front 150 mm drum brake was introduced.
The R32 (R for Rad meaning wheel but the 32 remains a mystery) was also surprisingly light at 122 kg and offered a top speed of around 90 km/h. The low centre of gravity, short 1380 mm wheelbase and 26-inch wheels promised safe and manageable handling for a touring motorcycle on the poor quality roads of the day.
In May 1923, Friz himself tested the R32, finishing the “Fahrt durch Bayerns Berge” trial through the Bavarian mountains without incurring any penalties.
The R32 was launched at Berlin in September 1923, one month before the Paris Car Show where it was a star attraction, establishing BMW’s boxer-twin shaft-drive format. Despite its impressive credentials the initial response to the R32 was mixed.
Sceptics feared the engine could be easily damaged in a fall, others felt it underpowered, but no one could deny the compact engine and transmission unit was a brilliant design and beautifully executed.
As cars were for the wealthy few the motorcycle market flourished in Germany during the early 1920s, BMW managing to sell 1500 R32s by the end of 1924, with sales totalling 3,090 by the time production finished in 1926. Most were sold in Germany and it is estimated only around 60 survive today.
Despite its modest specification the R32 was the founder of the species and holds a special place in BMW’s history, serious collectors considering it the most desirable BMW motorcycle. The R32 was not only the first BMW motorcycle and their first boxer twin, it established a formula and DNA that has distinguished BMW motorcycles for one hundred years.
1923-1926 BMW R32 Specifications
| 1923-1926 BMW R 32 | |
| Engine Designation | M2 B33 or M33a |
| Type | Four-stroke, twin-cylinder, flat-twin |
| Bore x stroke | 68 x 68 mm |
| Displacement | 494 cc |
| Power | 8.5 hp at 3200 rpm |
| Compression ratio | 5.0:1 |
| Valves | Side valve |
| Carburetion | BMW Special 22 mm |
| Gears | Three-speed |
| Ignition | Bosch magneto |
| Frame | Twin-loop tubular steel |
| Front suspension | Twin cantilever spring |
| Rear suspension | Rigid |
| Wheels | 26 x 2.50 |
| Tires | 26 x 3.00 front and rear |
| Brakes | 150 mm front drum (second series) block rear |
| Wheelbase | 1380 mm |
| Dry weight | 122 kg |
| Numbers produced | 3090 |
