1955 BMW Isetta 250 54

The Isetta was one of the most successful microcars produced in the post-World War II years—a time when cheap, short-distance transportation was most needed. Although the design originated in Italy, it was built in a number of different countries, including Spain, Belgium, France, Brazil, Germany, and the United Kingdom. Because of its egg shape and bubble-like windows, it became known as a bubble car—a name later given to other similar vehicles.

The Isetta caused a sensation when it was introduced to the motoring press in Turin in November 1953, it was unlike anything seen before. Small (only 2.29 m (7.5 ft) long by 1.37 m (4.5 ft) wide) and egg-shaped, with bubble-type windows, the entire front end of the car hinged outwards to allow entry and in the event of a crash, the driver and passenger were to exit through the canvas sunroof. The steering wheel and instrument panel swung out with the single door, as this made access to the single bench seat simpler. The seat provided reasonable comfort for two occupants, and perhaps a small child. Behind the seat was a large parcel shelf with a spare wheel located below. A heater was optional, and ventilation was provided by opening the fabric sunroof.

Power came from a 236 cc (14.4 in³), 7.1 kW (9.5 hp) two-cylinder two-stroke motorcycle engine. The engine was started by a combination generator-starter known as Dynastart. A manual gearbox provided four forward speeds and reverse. A chain drive connected the gearbox to a solid rear axle with a pair of closely-spaced 25 cm (10 in) rear wheels. The first prototypes had one wheel at the rear; this made the car prone to roll-overs, so they placed two rear wheels 48 cm (19 in) apart from each other. This narrow track eliminated the need for a differential. The front axle was a modified version of a Dubonnet independent front suspension. The Isetta took over 30 seconds to reach 50 km/h (31 mph) from rest. Top speed was only about 75 km/h (47 mph). The fuel tank held only 13 litres (3.5 gallons). However, the Isetta would get somewhere between 50 mpg-imp (5.6 L/100 km; 42 mpg-US) and 70 mpg-imp (4.0 L/100 km; 58 mpg-US) depending on how it was driven.

Two models were offered - the little egg-shaped Turismo with narrow 50 cm (20 in) rear track, and the Autocarro, a commercial version with full-width rear axle. The Autocarro was offered in several body styles, a flatbed pickup, enclosed truck, a tilt-bed, or even a fire engine. The Autocarro was an extremely popular type of vehicle in Italy, and numerous manufacturers produced some variant of the type. Iso had previously produced a motorcycle-type Isocarro. The Iso Autocarro was larger than most, with its four-wheel layout, conventional rear axle with differential and leaf springs, and a large tubular frame. It was good for a 500-600 kg (1,102-1,323 lb) load. The name Isetta Autocarro was also used.

In 1954, Iso entered several Isettas in the legendary Mille Miglia where they took the top three spots in the economy classification: over a distance of 1,600 km (1,000 mi) the drivers achieved an average speed of over 70 km/h (43 mph). In view of its maximum speed, which was just 15 km/h (9 mph) higher, this was an almost incredible figure. However, despite its initial success, the Isetta was beginning to slip in popularity at home. This was mainly due to renewed competition from FIAT with its 500C model.

Renzo Rivolta wanted to concentrate on his new Iso Rivolta sports car, and was extremely interested in doing licencing deals. Plants in Spain and Belgium were already assembling Isettas and Autocarros using Italian made Iso components. BMW began talking with Rivolta in mid-1954 and bought not just a licence but the complete Isetta body tooling as well. Rivolta didn't stop with licencing the Isetta to BMW. He negotiated similar deals with companies in France and Brazil.

BMW Isetta 250

2 tone coloured BMW Isetta 250

While it retained the "Bubble Window" styling, it differed from the Italian model in that its headlamps were fixed separately to the sides of the bodywork and it carried the BMW badge below the windscreen. The car was also redesigned to take a modified version of the 250 cc four-stroke engine from the BMW R25/3 motorcycle and the front suspension was changed. The single-cylinder generated 9 kW (12 hp) at 5800 rpm. The crankcase and cylinder were made of cast iron, the cylinder head of aluminium. However, the head was rotated by 180° compared with the motorcycle engine. The twin-bearing crankshaft was also different in the Isetta power unit, being larger and featuring reinforced bearings. One of the reasons for this was the heavy Dynastart unit which combined the dynamo and self-starter. The fuel mixture was provided by a Bing sliding throttle side draft motorcycle carburetor. In addition to further changes of detail, the BMW engineers enlarged the sump for installation in the car and cooled the engine by means of a radial fan and shrouded ducting.

The power train from the four-speed gearbox to the two rear wheels was also unusual: fixed to the gearbox output drive was something called a Hardy disc, which was a cardan joint made of rubber. On the other side of it was a cardan shaft, and finally a second Hardy disc, which in turn was located at the entrance to a chain case. A duplex chain running in an oil bath led finally to a rigid shaft, at each end of which were the two rear wheels. Thanks to this elaborate power transfer, the engine-gearbox unit was both free of tension and well soundproofed in its linkage to the rear axle.

In Germany, the Isetta could even be driven with a motorcycle license. The top speed of the Isetta 250 was rated as 85 km/h (53 mph).

The first BMW Isetta rolled off the line in April 1955, and in the next eight months some 10,000 of the "bubblecars" were produced.

This particular model commemorates King Ludwig of Bavaria, builder of Neuchwanstein Castle and patron of the opera composer Richard Wagner

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