Sinclair C5 Isetta, a 1960s Italian microcar. Sinclair built a full-scale mock-up of it; according to Wood Rogers, "it looked great. I specified open sides to keep the cost down and having no doors meant it escaped a lot of regulations too." The design is strikingly similar to the modern Renault Twizy electric vehicle; Wood Rogers comments that "you could put the C10 into production today and it would still look contemporary." At the time of the C5's launch, Sinclair described the C15 as having "a futuristic design with an elongated 'tear-drop' shape, a lightweight body made of self-coloured polypropylene and a
Sinclair C5 expensively) on the aerodynamics rather than the cycle technology around which the C1 was based. The weight of the vehicle increased to over , far more than Sinclair's desired specification. By March 1983, Sinclair and Wood Rogers had decided to stop the C1 programme. Wood Rogers comments that Ogle were convinced that the C1 would be a flop, telling Sinclair that it would not be fast enough, that its drivers would get wet when it rained and that the battery was not good enough. To meet the steadily escalating development costs of the vehicle, Sinclair decided to raise capital by