User:DerekvG/sandbox/Classic Mini: Design History

Design and development

1959 Morris Mini-Minor interior

Cross-section shows how Mini maximises passenger space

Designated by Leonard Lord as project ADO15 (Amalgamated Drawing Office project number 15) and the product of the Morris design team, the Mini came about because of a fuel shortage caused by the 1956 Suez Crisis. Petrol was once again rationed in the UK, sales of large cars slumped, and the market for German bubble cars boomed. Lord, the somewhat autocratic head of BMC, reportedly detested these cars so much that he vowed to rid the streets of them and design a 'proper miniature car'. He laid down some basic design requirements: the car should be contained within a box that measured 10×4×4 feet (3.0×1.2×1.2 m); and the passenger accommodation should occupy 6 feet (1.8 m) of the 10-foot (3.0 m) length; and the engine, for reasons of cost, should be an existing unit. Issigonis, who had been working for Alvis, had been recruited back to BMC in 1955 and, with his skills in designing small cars, was a natural for the task. The team that designed the Mini was remarkably small: as well as Issigonis, there was Jack Daniels (who had worked with him on the Morris Minor), Chris Kingham (who had been with him at Alvis), two engineering students and four draughtsmen. Together, by October 1957, they had designed and built the original prototype, which was affectionately named "The Orange Box" because of its colour.

The ADO15 used a conventional BMC A-Series four-cylinder, water-cooled engine, but departed from tradition by mounting it transversely, with the engine-oil-lubricated, four-speed transmission in the sump, and by employing front-wheel drive. Almost all small front-wheel-drive cars developed since have used a similar configuration, except with the transmission usually separately enclosed rather than using the engine oil. The radiator was mounted at the left side of the car so that the engine-mounted fan could be retained, but with reversed pitch so that it blew air into the natural low pressure area under the front wing. This location saved vehicle length, but had the disadvantage of feeding the radiator with air that had been heated by passing over the engine. It also exposed the entire ignition system to the direct ingress of rainwater through the grille.

The suspension system, designed by Issigonis's friend Dr. Alex Moulton at Moulton Developments Limited, used compact rubber cones instead of conventional springs. This space-saving design also featured rising progressive-rate springing of the cones, and provided some natural damping, in addition to the normal dampers. Built into the subframes, the rubber cone system gave a raw and bumpy ride accentuated by the woven-webbing seats, but the rigidity of the rubber cones, together with the wheels' positioning at the corners of the car, gave the Mini go kart-like handling.

Initially an interconnected fluid system was planned, similar to the one that Alec Issigonis and Alex Moulton were working on in the mid-1950s at Alvis. They had assessed the mechanically interconnected Citroën 2CV suspension at that time (according to an interview by Moulton with Car Magazine in the late 1990s), which inspired the design of the Hydrolastic suspension system for the Mini and Morris/Austin 1100, to try to keep the benefits of the 2CV system (ride comfort, body levelling, keeping the roadwheel under good control and the tyre in contact with the road), but with added roll stiffness that the 2CV lacked. The short development time of the car meant this was not ready in time for the Mini's launch. The system intended for the Mini was further developed and the hydrolastic system was first used on the Morris 1100, launched in 1962; the Mini gained the system later in 1964. Ten-inch (254 mm) wheels were specified, so new tyres had to be developed, the initial contract going to Dunlop. Issigonis went to Dunlop stating that he wanted even smaller, 8 in (203 mm) wheels (even though he had already settled on ten-inch). An agreement was made on the ten-inch size, after Dunlop rejected the eight-inch (203 mm) proposition.

Sliding windows allowed storage pockets in the hollow doors; reportedly Issigonis sized them to fit a bottle of Gordon's Gin. The boot lid was hinged at the bottom so that the car could be driven with it open to increase luggage space. On early cars the number plate was hinged at the top so that it could swing down to remain visible when the boot lid was open. This feature was later discontinued after it was discovered that exhaust gases could leak into the cockpit when the boot was open.

The Mini was designed as a monocoque shell with welded seams visible on the outside of the car running down the A and C pillars, and between the body and the floor pan. Those that ran from the base of the A-pillar to the wheel well were described as 'everted' (lit., 'turned outward') to provide more room for the front seat occupants. To further simplify construction, the hinges for the doors and boot lid were mounted externally.

Production models differed from the prototypes by the addition of front and rear subframes to the unibody to take the suspension loads, and by having the engine mounted the other way round, with the carburettor at the back rather than at the front. This layout required an extra gear between engine and transmission to reverse the direction of rotation at the input to the transmission. Having the carburettor behind the engine reduced carburettor icing, but the distributor was then exposed to water coming in through the grille. The engine size was reduced from 948 to 848 cc (57.9 to 51.7 cu in); this, in conjunction with a small increase in the car's width, cut the top speed from 90 mph (140 km/h) to 72 mph (116 km/h).