page_title: Chapman strut
section_title: Chapman's design
hierarchical_section_title: Chapman strut / Origins / Chapman's design
caption_attribution_description: English: Rear Chapman strut suspension of a Lotus Twelve Formula One car.
context_page_description: The Chapman strut is a design of independent rear suspension used for light cars, particularly sports and racing cars. It takes its name from, and is best known for its use by, Colin Chapman of Lotus.
  The characteristic feature of the Chapman strut is a long upright strut combining a coil spring and shock absorber, with a universal-jointed drive shaft itself forming the lower link of the suspension.
context_section_description: In 1956 Chapman was using de Dion rear axles for his Lotus racing cars and also the Vanwall. These had initially used transverse leaf springs, but later changed to coilover shock absorbers. Chapman had identified some of the de Dion's disadvantages as including its high unsprung weight, the need for sliding splines in the rear driveshafts, and also (a typical Chapman fixation) its insensitivity to changes in weight as fuel is consumed. The first Lotus Twelve Formula 2 cars used the same system, although the de Dion's mass was a drawback for a lightweight single-seater racing car.
  At a 750 Motor Club meeting in 1957, Chapman saw the Goggomobil system and was impressed by its Lotus-like simplicity and light weight. The use of the drive shafts for both drive and as a suspension component appealed to Chapman, who always favoured solutions that could make one component do double duty. 
  Chapman struts were introduced in Lotus' first single-seater car, the Lotus Twelve. This was developed as a 1.5-litre Formula 2 in 1957, but re-engined in 1958 it also competed in Formula 1. This same car also introduced Lotus' wobbly-web wheel.
  There were two differences from these precursors to the Chapman strut. As the Lotus Twelve had inboard disk brakes, there was no need to pass the braking torque through the radius rods. Chapman also avoided the swing axle and its camber changes with suspension travel, in favour of a drive shaft with two universal joints. The connection between the hub carrier and the shock absorber base was made rigid, making the spring unit into a strut and also controlling the camber angle. Using the drive shaft itself to control the rear track meant that the shaft could be of fixed length, avoiding the need for a sliding spline joint and its stiction problems.
  Chapman applied for a patent on his strut design on 13 June 1957.
  The Chapman strut also appeared on the Lotus Sixteen of 1958. In 1959 this design was revised to use a lower wishbone. This in turn required a return to a sliding joint in the drive shaft.
caption: Lotus Twelve. The strut spring, driveshaft below and radius rod can just be seen
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