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Country of origin:Great Britain
Produced from:1962 - 1963
Numbers built:7
Predecessor:Lotus 24 Climax
Successor:Lotus 33 Climax
Author:Wouter Melissen
Last updated:December 21, 2009
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Click here to download printer friendly versionBig advances in tire development and new regulations for 1961 forced Formula 1 designers to come up with cars both rigid and light. The old tires complete lack of grip benefited from a somewhat flexible chassis for easy sliding around, but by the early sixties the newly found grip levels were a big strain on the traditional tubular frame chassis. Ironically right at this time the sport's governing body decided to decrease the maximum displacement from 2.5 to 1.5 litres. With less power available, saving weight was now a top priority for the designers, but this in turn usually came at the expense of the rigidity. More than anybody, Lotus' Colin Chapman also understood that decreasing the frontal area was of the utmost importance for a competitive design. With these three variables in the back of his mind, Chapman came up with a Formula 1 racer that would revolutionize single seater design and turn Lotus into a regular winner.

Chapman's first purpose built '1.5 litre' racer was the Lotus 24, which used a conventional spaceframe chassis combined with the newly developed Coventry Climax V8 engine. To lower the drag, the cigar shaped body was very slim with the driver almost flat on his back. To make this narrow body possible, the fuel tanks were moved from the sides to above the driver's legs, which resulted in a relatively high polar moment and prevented an even flatter position of the driver. The '24' was very light and narrow, but with the spaceframe chassis, it was still not free of flex. Being intended mainly as a customer car, the Lotus 24 design and production was by no means a secret, which was not the case for the operation in one corner of the factory. For the works team, Lotus was working on a car that was as small and light as the '24', but would also be stiff enough to make the most of the latest tires and the 24's advanced suspension geometry.

At a lunch time meeting with aerodynamics expert and long time associate Frank Costin, Colin Chapman came up with the groundbreaking idea for his new Formula 1 racer. He returned home with some sketches on a napkin and turned them into the design for the first single seater monocoque. While the monocoque principle of the body being the chassis was by no means new, but it was never used for a single seater racer. One of the rare purpose built monocoque racing cars was the Jaguar D-Type, but the weight and complexity of the construction did not make it seem a viable option.

Chapman's design was much more straightforward and consisted of two aluminium pontoons that formed the sides of the car. The two structures were held together on either end by a firewall, creating a tub, which together with subframes for the front and rear suspension formed the chassis. The V8 engine was installed as a semi-stressed member and further increased the rigidity. The aluminium pontoons doubled as fuel tanks allowing for an even lower driving position. Compared to the spaceframe 24, the rigidity of the new, equally light '25' was substantially higher. Using a monocoque was by no means a compromise; the additional benefits were numerous. Only the bottom half of the car was part of the chassis with the rest made up of removable glass reinforced plastic body panels that allowed easy access to all vital parts.

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  Article Image gallery (75) Chassis (2) Specifications User Comments (3)