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1963-65 The Lotus revolution
At the end of a lunch, in a restaurant near Lotus facility, Colin Chapman, founder and owner of the Team, was looking for an innovative solution for his future model 25. The result of this moment of inspiration was recorded on a paper napkin and caused the greatest technical change in Formula 1 and motorsport.
A few years earlier, John Cooper revolutionized Formula 1 by imposing his central rear engine powered Cooper-Climax over the most powerful competitors with classic front engine. For 1961 the technical regulations imposed a 1,5-liter capacity limit to the engines and Ferrari reacted quickly to this change, winning that year’s Drivers and Constructors Championships, with Phil Hill and the 156 “sharknose” model.
For 1962, Team Lotus, which made its debut in Formula 1 in 1959 and won its first Grand Prix at Monaco in 1960, with Stirling Moss at the wheel of the model 18, prepared the model 21, later evolved into the 24, all powered by the Coventry Climax 1,5-liter engine.
For the Dutch GP, at the Zandvoort circuit, Chapman presented a brand-new Lotus 25, to Jim Clark, who, to the general surprise, used a revolutionary monocoque chassis.
This type of chassis had already been used by Jaguar, in Type D, which had a hybrid chassis, partially tubular and with the central cell around the cockpit, in monocoque structure. In this technology, the chassis has a continuous structure, in the same type of material, which gives it a high torsional rigidity.
In the case of the Lotus 25, this structure consisted of bended and welded aluminum alloy panels, which formed two long D-shaped longitudinal boxes, joined together on the floor by another box and by bulkheads placed one ahead, at the front end of the chassis, another centrally, which served as support for the steering wheel and the instrument panel and the third to support the roll bar, at the rear limit of the cockpit. The chassis extended backwards and supported the engine, ending with a final bulkhead where the rear suspension elements were anchored. The driver was installed in a more reclined position than usual for the time and the side boxes accommodated fuel tanks in a flexible material.
The chassis was very narrow and low, with a reduced frontal area, with evident gain in aerodynamic penetration. The low weight of the chassis (about half of its predecessor), combined with the significant increase in torsional stiffness (for triple when compared to the previous model), allowed the use of a very smooth suspension, which made it very easy to drive in sharp turns.
The suspensions used lower wishbones, complemented by a tilting arm at the front and cross and longitudinal rods at the rear. The shock absorbers/coil springs completed the suspensions and, at the front, were housed inside the bodywork.
The engine was the usual Coventry Climax with 1,5-liters V8 at 900, which delivered about 195bhp at 8,200rpm. Power transmission was provided by a 5-speed manual ZF gearbox. The brakes were disc and the tires were supplied by Dunlop.
The new Lotus model was competitive from the start and Jim Clark won three GP races that year, only losing the Championship to Graham Hill due to reliability problems. In 1963, having overcome these problems, Lotus and Jim Clark, seconded by Trevor Taylor, would win, for the first time, the Constructors and Drivers’ World Championships, with seven GP victories. Seven cars of this model were built, which won 14 GP races and remained competitive until 1965, inscribed by the works and client teams.
In 1964, Lotus introduced the new 33 model, designed by Colin Chapman in partnership with Len Terry. Although very similar, the new car represented an evolution of the 25, with superior torsional rigidity, simpler and easier to build and with suspensions adapted to the use of the new, wider tires. The engine was the same Coventry Climax that, equipped with a distribution of 4 valves per cylinder, delivered about 220bhp.
In 1965 and after overcoming the youth problems of the new model, Jim Clark won 5 GP races (in addition to the Indianapolis 500 Miles), and, seconded by Mike Spence, won, again, the two World Champion titles for Lotus.
Six model 33 cars were built and remained active and competitive until 1967, powered from 1966, by 2-liters V8 engines from Coventry Climax and BRM.