It is no overstatement to say that the Lotus 25 revolutionized Formula 1 car design. It was a complete break from conventional thinking, advanced even for Colin Chapman, and its significance must be one of the best-kept secrets in motor racing. Colin Chapman said the inspiration came from the steel backbone frame of the new Lotus Elan and the improved stiffness it gave. Would it work on a single seater? The idea came about from a meeting with Mike Costin, from which Chapman went home with a napkin and some sketches.
Although the Lotus 25 was not the first monocoque single-seater racing car, it was the first to prove the efficacy of monocoque design in Grand Prix racing. Based around two D-section tubes placed back to back and held in place with fabricated front and rear bulkheads, the chassis drew further strength from the instrument panel and seat back. Having the engine and gearbox bolted directly to it helped boost rigidity as well. This design was the brainchild of Colin Chapman and the car was arguably the grandfather of all current-day Grand Prix cars.