It was designed and developed to give Saab, then a new arrival in the automotive industry, a competitive entry into international sports car racing. The small team behind the project was unimpressed by the use of heavy steel tubes that were welded together to create the chassis of competition cars at the time. They found an alternative solution in aircraft design. The result was a light but extremely strong ‘monocoque’ (single shell) structure made from riveted panels of aviation specification aluminum, to which the engine and suspension was directly mounted.
Weighing just 70 kilos, the Sonett’s hollow ‘tub’ utilised the elegant design principles of an aircraft fuselage. It was built six years before a similar concept revolutionised Grand Prix racing in the shape of Colin Chapman’s Lotus 25 Formula One car. The car’s low-slung bodywork was no less surprising. Based on a small-scale model by Saab designer Sixten Sason, it was moulded in glass-fiber reinforced plastic (GRP), a new material at the time. Sason complained about the shaping of the panels but GRP was chosen as it was much lighter than steel, even though the use of such a material was in its infancy.
The Sonett’s engine was rather more conventional. It was a highly-tuned development of the 748cc, three cylinder two-stroke engine from the Saab 93 sedan. To improve weight distribution, the longitudinally mounted engine and gearbox were turned around through 180°. While still using front-wheel-drive, this installation gave the car a front, mid-engined configuration, with the weight of the entire powertrain contained within the car’s wheelbase. For good balance, the 60-liter fuel tank was also mounted in the side of the car opposite the driver. And to keep the front of the car as low as possible, the engine was canted over slightly to the right.
Maximum power of 57,5 hp was modest for circuit racing, but with an all-up weight of only 500 kilos, the Sonett Super Sports had a good power-to-weight ratio of more than 100 bp per tonne. A rigid chassis giving nimble handling was also expected to compensate for whatever it lacked in outright power. The first prototype created a sensation at the Stockholm Motor Show in February 1956 and a test program immediately began. To speed up development work, another five Sonetts, with steel monocoques, were built. However, before a racing program got underway, new competition rules tempted Saab into international rallying with production-based cars as a more cost-effective operation.