| MODEL | BMW R 66 1938 - 1941 |
| Year | 1938 - 1941 |
| Engine Type | Four stroke, two cylinder horizontally opposed boxer, OHV, 2 valves per cylinder |
| Displacement / Capacity | 597 cc / 36.4 cu in |
| Bore X Stroke | 69.8 x 78 mm |
| Compression Ratio | 6.8:1 |
| Cooling System | Air cooled |
| Max Power | 22 kW / 30 hp @ 5300 rpm |
| Max Torque | — |
| Ignition | Battery ignition |
| Induction | — |
| Start System | Kick |
| TRANSMISSION SPECS | |
| Lubrication | — |
| Gear Box | 4 Speed |
| Clutch | Single plate, dry |
| Final Drive | Shaft |
| CHASSIS SPECS | |
| Frame | Double loop tubular steel |
| Front Suspension | Telescopic fork |
| Rear Suspension | Plunger (straight-line) suspension |
| Front Brakes | 200 mm drum |
| Rear Brakes | 200 mm drum |
| DIMENSION SPECS | |
| Overall Length | 2130 mm / 83.9 in |
| Overall Width | 815 mm / 32.1 in |
| Overall Height | 960 mm / 37.8 in |
| Seat Height | 700 mm / 27.6 in |
| Wheelbase | 1400 mm / 55.1 in |
| Ground Clearance | — |
| Dry Weight | — |
| Wet Weight | 187 kg / 412 lbs |
| WHEEL SPECS | |
| Front Tyre | 3.50-19 |
| Rear Tyre | 3.50-19 |
| FUEL SYSTEM | |
| Fuel Capacity | 14 Litres / 3.7 US gal |
| Fuel Consumption | 4.5 L/100 km |
| Top Speed | 145 km/h / 90 mph |
The sporting flagship of BMW's 1938 range, the R 66 paired a new 600 cc overhead-valve flat twin with telescopic forks and the plunger rear suspension that BMW had proven in the previous year's Six Days Trial. With 30 hp it was the fastest pre-war BMW road machine, but it was expensive and sold in far smaller numbers than the R 51. Production ended in 1941 as wartime output took over.
