DKW had made its name in the prewar period with its range of budget light cars. After the war, the company restarted personal vehicle production with the F89P New Meisterklasse, which had been developed in the prewar period as a budget middle-priced car, Although the Meisterklasse was a strong seller, the company had no budget car offering in the market. Observing the success of microcars, such as the "Messerschmitt", "Zündapp" and "Isetta BMW" types, the company decided it would be a good idea to introduce a budget vehicle that would occupy a position below the F89P and so in 1952 a microcar project was initiated in the motorcycle department. The project was entrusted to a ghost at Auto-Union - Eberan von Eberhorst who had made himself famous before the war by developing the C and D type "Silver Arrows" (left in photo below).
The first study was for a car weighing no more than 250kg, capable of carrying a payload of 225kg, amounting to three people and their luggage, at a speed of around 75km/h. The new car would be priced 40% lower than the VW Beetle. Plastic bodywork would be used to achieve the minimum weight requirements. The first sketch presented was called the "STM I".
A wood and metal frame was constructed to test the concept for habitability, followed a plaster model. The STM 1 had no real doors, access being by lifting the whole of the roof and the windshield, a little like the Messerschmitt. A stationary engine of between 200 to 350ccs would provide the powerplant, which gave the project its name - "STM" being the abbreviation of "Stationär Motor."
Ultimately, the idea of building a very small car was abandoned in favor of a machine that was more robust and could compete with the VW Beetle. The small displacement engine and the plastic bodywork, however, remained an integral part of the specifications. This resulted in the "STM II" version. It still had 3 seats with the driver seated centrally, but remained of rather questionable aesthetics.
Von Eberhorst's team continued refining the specifications, ultimately resulting in a 4-seater light weight car. This version was designated "STM III." The problem for Auto-Union was the development of the plastic body. Auto-Union had experimented extensively with phenolic resin impregnated paper and/or fabric panels during the prewar period. This technology would finally be developed successfully in the East with the "Trabant." Auto-Union however was experimenting with polyether glass fibre, like that used by Chevrolet in its Corvette, the very first production car with a plastic body.
But the development of plastic body panels had not yet been mastered and to obtain consistent panels of 2.5mm thick it was necessary to use presses of very high power but whose forming time was around 3 minutes, which was hardly compatible with mass production. Auto-Union was planning to produce 300 vehicles per day, which would require multiplying the number of presses beyond Auto-Union's budget. The firm therefore appealed to the State to obtain a subsidy. During this time the trials and tests of the prototype "STM III" continued, with the car covering more than 800,000 kms with satisfactory results. Some selected dealers were even called in to garner their opinions. Although the car's finish was rather spartan side and the lack of access to the luggage compartment from the outside received criticism, the dealers were generally positive.
State funding required the prototype to be presented to a government commission for evaluation in August 1956. However, in early 1957 there was a change in leadership at Auto-Union and the new general director, William Werner, challenged the safety of the car's mixed plastic and steel construction. In another exercise of the chronic indecision at Auto-Union, which had several years earlier aborted the promising FX project, Werner put an end to the project.
Disappointed, von Eberhorst left Auto-Union, followed by many of his team. The car disappeared but ten years later the prototype STM III was discovered in the depths of a reserve at VW in Wolfsburg. The car had been used as a test bench on the private VW test circuit, but its condition was still good enough to undertake a restoration. This is the car that you can see today at the Ingolstadt museum. This late STM III prototype contained several stylistic elements of the future DKW "600", which would go on to become the "Junior", such as the fold of rear wing, shape of the windshield, rear window and 12 inch wheels. The indecision of the Auto-Union leadership would continue with the inability to develop a model capable of succeeding the aging "1000." Despite the "F102” and given the withdrawal of Daimler-Benz from Auto-Union, VW would come to sound the death knell for cars with a two-stroke engine.
The STM III prototype on display at Audi Tradition
For the aborted FX project - https://dkwautounionproject.blogspot.com/2017/10/the-dkw-fx-would-be-successor.html
For the STM project's part in the decline of DKW - https://dkwautounionproject.blogspot.com/2019/08/auto-unions-small-car-odyssey.html
For the decline of DKW - https://dkwautounionproject.blogspot.com/2019/06/the-decline-of-dkw.html
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