Comparison of BMW R51 1939 and BMW R66 1940 [S]ave
| Attribute |  BMW R66 1940 × |  BMW R51 1939 × |
|---|---|---|
| General | ||
| Production from (year) | 1940 | 1939 |
| Make | BMW | BMW |
| Model | BMW R66 | BMW R51 |
| Category | Allround | Allround |
| Engine and transmission | ||
| Engine type | Two cylinder boxer, four-stroke | Two cylinder boxer, four-stroke |
| Fuel system | Carburettor. 26mm | Carburettor. Amal |
| Displacement (cm³) | 596 | 494 |
| Power (kw) | 21.9 | 17.6 |
| Cooling system | Air | Air |
| Transmission type,final drive | Shaft drive (cardan) | Shaft drive (cardan) |
| Bore (mm) | 69.8 | 68 |
| Stroke (mm) | 78 | 68 |
| Gearbox | 4-speed | 4-speed |
| Fuel control | Overhead Valves (OHV) | Overhead Valves (OHV) |
| Ignition | Forced feed | Battery |
| Clutch | Dry-single plate-cable operated | Dry-single plate-cable operated |
| Lubrication system | Wet sump | Wet sump |
| Compression | 6.8:1 | 6.7:1 |
| Chassis | ||
| Front suspension | Cartridge | Cartridge |
| Rear suspension | Twin shock-Swingarm | Twin shock-Swingarm |
| Front brakes | Expanding brake (drum brake) | Expanding brake (drum brake) |
| Rear brakes | Expanding brake (drum brake) | Expanding brake (drum brake) |
| Diameter (mm) | 200 | 200 |
| Frame type | Doble steel loop | Steel single cradle |
| Front tyre | 3.5-19 | 3.50-19.00 |
| Rear tyre | 3.5-19 | 3.50-19.00 |
| Seat | Single seat | Single seat |
| Wheels | Spoked | - |
| Other | ||
| Starter | Kick | Kick |
| Carrying capacity | 210kg-500kg with sidecar | - |
| Dimensions | ||
| Wheelbase (mm) | 1,400 | 1,400 |
| Kerb weight (kg) | 187 | 182 |
| Overall height (mm) | 960 | 960 |
| Overall length (mm) | 2,130 | 2,130 |
| Overall width (mm) | 815 | 815 |
| Performance | ||
| Top speed (km/h) | 145 | 140 |
| Fuel capacity (l) | 14 | 14 |
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