It was the first mid-engined car built by Lotus and was a marked improvement over Chapman's early and only moderately successful front-engined formula cars, the 12 and 16.
It was introduced for the 1960 F1, F2 and FJ seasons.
The Lotus 18 had run successfully in 1960 and had been powered by a 2.5litre Coventry Climax FPF engine but for 1961 the FIA had introduced a smaller 1.5 litre engine limit.
The Lotus 18/21 was a stop-gap before the introduction of the 18's successor models, the Lotus 20 and 21.
Some 18 chassis were rebodied with 21 skins to create the interim Lotus 18/21 hybrid derivative. These Lotus 18/21 hybrid derivative units used a Coventry Climax 1.5 litre engine to suit the FIA rating.
The car was a classic Chapman design, being extremely light and simple; the body was made up of lightweight panels bolted to heavily-triangulated tube frame (almost spaceframe) chassis. Thus the car was rigid and strong, maintaining the 16's forward weight distribution despite the engine moving behind the driver.
It was powered initially by a 2,494.93 cc Coventry Climax (3.70 x 3.54 in) four cylinder engine inherited from the Lotus 16 which produced 239 hp (178 kW) at 6,750 rpm from a weight of only 290 lbs (132 kg) and had a wide torque range. In order to capitalize on this weight advantage, Chapman designed a light, sleek machine only 28 inches (71 cm) high (excluding windscreen) and weighing just 980 lbs (440 kg). To help facilitate this, the driver was placed in a semi-reclining position, pioneered about a decade before by Gustav Baumm of NSU.
The Lotus 18 had remarkably good handling with a unique suspension system which drastically reduced weight transfer and body roll in cornering. Shortly, the Lotus 18 was proving to be faster than any car Grand Prix racing had ever seen, eclipsing even the legendary Auto Unions and being widely copied. It was also built as a two-seat sports-racer called the Lotus 19 or Monte Carlo.
Grand Prix success
The car took Lotus' first F1 victory, by Innes Ireland in the non-championship Glover Trophy, in 8 April 1960. Its first World Championship win happened six weeks later, in 29 May, albeit by privateer Rob Walker, who leased the car from Chapman. Driven by Stirling Moss the car took a dominant win at the 1960 Monaco Grand Prix. It was an early taste of things to come. Moss also won the United States Grand Prix at the end of the season helping Lotus finish second in the constructors' championship.
Moss repeated his win in a legendary race at Monaco the following year, beating off the more powerful and faster 'sharknose' Ferraris. He then won at the fearsome Nürburgring in changeable weather, while Innes Ireland took a third win in the USA to help Lotus finish second in the constructors' championship in 1961. The Lotus 18 was also notable for giving Jim Clark his first Grand Prix start in 1960.
The 2.5 litre engine was replaced by a 1.5 litre Climax with new Formula One engine rules in 1961, and a Formula Junior variant used a 998 cc Ford MAE. The Formula Junior version also used smaller gauge chassis tubing and Alfin drum brakes on all four corners as it did not have to cope with so much power.
The 18 was replaced by the Lotus 21 in Formula One and the Lotus 20 in Formula Junior in 1961.