After Aston Martin rejected proposals for a replacement for its DB5 from the original DB4 Touring of Milan, the decision was made to focus on their own development car, registered 4 YMC. Wind tunnel testing, begun in February 1965, showed development was necessary to counteract a tendency toward aerodynamic lift result of the fastback styling causing reduced rear-wheel traction at high speed. Final development phases relied upon DB5 chassis, suitably lengthened and titled "MP 219", with rear lip-spoiler and abbreviated Kammback tail Aston Martin previously incorporated in sports-racing prototypes. The decision was made to produce "MP 219" as the Aston Martin DB6 although the prototype de Dion rear axle was rejected, Aston's soldiering on with its live-axle configuration reducing time to market, cost and complexity.