Colin Chapman began the design of the Lotus Eleven with a clean sheet of paper; the progression from Lotus 6 through 8, 9 and 10 was not continued. The chassis of the Eleven was made of steel tubes, and a body of aluminium panels by Frank Costin. Williams & Pritchard fabricated the body panels. There were a number of options including deDion rear suspension or simpler Austin live rear axle. Standard power units were the 1098cc Coventry-Climax FWA or the bigger 1460cc FWB from the same stable. However a variety of power units were fitted ranging from Ford 1172cc sidevalve, Maserati, Saab, and even Buick engines. Most track victories, including World Speed records came in the 1100cc class during 1956, 1957 and 1958. There were two body styles, a two-seater with full width windscreen, and a single-seater with prominent single headrest behind the driver. In Spring 1957 the Series II went into production with improvements to drivetrain for larger engines and suspension changes to give better handling. In 1958 Lotus launched the Lotus 15, a car somewhat similar to the Lotus 11, but in fact the body was separately developed by Williams & Pritchard without Frank Costin, and underneath there was a lot of re-engineering. Lotus 15 were usually fitted with the new Coventry-Climax FPF twin cam engines available from 1.5 to 2.5-litres. Lotus built just 27 Lotus 15s against 270 Lotus Elevens.