The Sinclair C5 is a small battery electric one-person recumbent tricycle, technically an "electrically assisted pedal cycle". It was the culmination of the English entrepreneur Clive Sinclair's long-running interest in electric vehicles. Although widely described as an "electric car", Sinclair characterised it as a "vehicle, not a car".
Sinclair had become one of the UK's best-known millionaires, and earned a knighthood, for his successful Sinclair Research range of home computers in the early 1980s. He hoped to repeat his success in the electric vehicle market, which he thought had potential for a new approach. The C5 emerged from an earlier project to produce a small electric car called the C1. After a change in the law, prompted by lobbying from bicycle manufacturers, Sinclair developed the C5 as an electrically powered tricycle with a polypropylene body and a chassis designed by Lotus Cars. It was intended to be the first in a series of increasingly ambitious electric vehicles, but the development of the follow-up C10 and C15 models never progressed, mostly due to the poor public response to the C5.
On 10 January 1985, the C5 was unveiled at a launch event, but it was received unenthusiastically by the British media. Its sales prospects were blighted by poor reviews and safety concerns expressed by consumer and motoring organisations. The vehicle's limitations – a short range, a maximum speed of only , a battery that ran down quickly and a lack of weatherproofing – made it impractical for most people's needs. It was marketed as an alternative to cars and bicycles, but ended up appealing to neither group of owners, and it was not available in shops until several months after its launch. Within three months of the launch, production had been slashed by 90%. Sales never picked up despite Sinclair's optimistic forecasts and production ceased entirely by August 1985. Out of 14,000 C5s made, only 5,000 were sold before its manufacturer, Sinclair Vehicles, went into receivership.
The C5 has been described as "one of the great marketing bombs of postwar British industry" and a "notorious ... example of failure". The C5 went on to become a cult item for collectors. Thousands of unsold C5s were purchased by investors and sold for hugely inflated prices, as much as £6,000 compared to the original retail value of £399. Enthusiasts have established owners' clubs and some have modified their vehicles substantially, adding bigger wheels, jet engines, and high-powered electric motors to propel their C5s at speeds of up to .
Design
The C5 is made predominantly of polypropylene, measuring long, wide, and high. It weighs approximately without a battery and with one. The chassis consists of a single Y-shaped steel component with a cross-section of about The vehicle has three wheels, one of diameter at the front and two of at the rear.
The driver sits in a recumbent position in an open cockpit, steering via a handlebar that is located under the knees. A power switch and front and rear brake levers are positioned on the handlebar. As a supplement to or replacement for electric power, the C5 can also be propelled via bicycle-style pedals located at the front of the cockpit. The maximum speed of an unmodified C5 is . At the rear of the vehicle is a small luggage compartment with a capacity of 28 litres (1 cu ft).Sinclair C5. A new power in personal transport. Sinclair Vehicles promotional brochure (January 1985) As the C5 does not have a reverse gear, reversing direction is done by getting out, picking up the front end and turning it around by hand.
The C5 is powered by a 12-volt lead–acid electric battery driving a motor with a continuous rating of 250 watts and a maximum 4,100 revolutions per minute. It is coupled with a two-stage gear-drive that increases torque by a factor of 13, without which the motor would not be able to move the vehicle when a person is on board. However, the motor is vulnerable to overheating. The torque increases as the load on the vehicle increases, for instance by going up too steep a gradient. Sinclair's tests showed that it could cope under power with a maximum slope of 1 in 12 (8%) and could manage a 1 in 7 (14%) slope using the pedals. As the speed of the motor reduces, the current flow through its windings increases, drawing up to 140 amps at stall speed. This would very quickly burn the motor out if sustained, so the motor's load is constantly monitored by the C5's electronics. If it stalls under full load the electronics disable the motor after 4 seconds, while if it is under heavy load (around 80 or 90 amps) it trips after two or three minutes. A heat-sensitive resistor inside the motor warns the driver if the vehicle is beginning to overheat and disconnects the motor after a short time, and a third line of defence is provided by a metallic strip mounted on the motor. If an excessive temperature is reached the strip distorts and the power is disconnected.
Although it was usually billed as an electric vehicle, the C5 also depends significantly on pedal power. The vehicle's battery is designed to provide 35 amps for an hour when fully charged or half that for two hours, giving the C5 a claimed range of . A display in the cockpit uses green, amber, and red LEDs to display the state of the battery charge. The segments are extinguished one after the other to indicate how much driving time is left. The last light indicates that only ten minutes of power are left, after which the motor is switched off and the driver is left to rely on the pedals. Another display indicates via green, amber, and red LEDs how much current is being used. The C5 is in its most economical running mode when a low amount of current, indicated by the green LEDs, is being used. When the lights are red, the motor is under a high load and the driver needs to use pedal power to avoid overheating and shutdown.
The C5 was initially sold at a cost of £399, but to keep the cost under the £400 mark a number of components were sold as optional accessories.Dale, p. 170 These included indicator lights, mirrors, mud flaps, a horn, and a "High-Vis Mast" consisting of a reflective strip on a pole, designed to make the C5 more visible in traffic. Sinclair's C5 accessories brochure noted that "the British climate isn't always ideal for wind-in-the-hair driving" and offered a range of waterproofs to keep C5 drivers dry in the vehicle's open cockpit. Other accessories included seat cushions and spare batteries."Sinclair C5 Accessories". Sinclair Vehicles promotional brochure (1985)
History
Origins Sir Clive Sinclair's interest in the possibilities of electric vehicles originated in the late 1950s during a holiday job for the electronics company Solartron. Fifteen years later, in the early 1970s, he was the head of his own successful electronics company, Sinclair Radionics, based in St Ives in Cambridgeshire. He tasked one of his employees, Chris Curry – later a co-founder of Acorn Computers – to carry out some preliminary research into electric vehicle design.
Sinclair took the view that an electric vehicle needed to be designed from the ground up, completely rethinking the principles of automotive design rather than simply dropping electric components into an established model. He believed that the motor was the key to the design. Sinclair and Curry developed a wafer-thin motor that was mounted on a child's scooter, with a button on the handlebars to activate it. The research got no further, however, as Sinclair's development of the first "slimline" pocket calculator – the Sinclair Executive and its successors – took precedence. No further work on electric vehicles took place for most of the rest of the 1970s.
Early development: the C1 It was not until late 1979 that Sinclair returned to electric vehicle development. Around Christmas that year, he approached Tony Wood Rogers, an ex-Radionics employee, to carry out consultancy work on "a preliminary investigation into a personal electric vehicle". The brief was to assess the options for producing a one-person vehicle which would be a replacement for a moped and would have a maximum speed of . Although Wood Rogers was initially reluctant, he was intrigued by the idea of an electric vehicle and agreed to help Sinclair. The vehicle was dubbed the C1 (the C standing for Clive). He built a number of prototypes to demonstrate various design principles and clarify the final specifications.Dale, p. 152
A specification of the C1 emerged by the end of the year. It would address short-distance transportation needs, with a minimum range of on a fully charged battery. This reflected official figures showing that the average daily car journey was only , while the average moped or pedal cycle journey was just . The users were envisaged as being housewives, urban commuters, and young people, who might otherwise use cycles or mopeds to travel. The electric vehicle would be safer, more weather-proof, and would offer space to carry items. It would be easy to drive and park and for the driver to enter or exit, and it would require minimum maintenance. The vehicle would be engineered for simplicity using injection-moulded plastic components and a polypropylene body. It would also be much cheaper than a car, costing £500 () at the most.Dale, p. 152–3
One area of development that Sinclair purposely avoided was battery technology. Electric vehicles powered by lead–acid batteries had once actually outnumbered internal combustion engine vehicles; in 1912 nearly 34,000 electric cars were registered in the U.S. However, the efficiency of internal combustion engines greatly improved while battery technology advanced much more slowly, leading to petrol and diesel-driven vehicles dominating the market.Adamson & Kennedy, p. 184 By 1978, out of 17.6 million registered vehicles on Britain's roads, only 45,000 were electric vehicles in day-to-day use and of those, 90% were milkfloats.Burton, p. 101 Sinclair chose to rely on existing lead–acid battery technology, avoiding the great expense of developing a more efficient type. His rationale was that if the electric vehicle market took off, battery manufacturers would step up to develop better batteries.Dale, p. 154 Wood Rogers recalls:
The development programme moved to the University of Exeter in 1982, where the C1 chassis was fitted with fibreglass shells and tested in a wind tunnel. It was recognised at an early stage that the vehicle would have to be aerodynamic; although it was only ever intended to be small and relatively slow, reducing wind resistance was seen as essential for the vehicle's efficiency. By March 1982, the basic design of the C1 had been established. Sinclair then turned to an established motor design company, Ogle Design of Letchworth, to provide professional styling assistance and production engineering. However, Ogle's approach was not to Sinclair's liking; they tackled the project as one of car design and focused more (and expensively) on the aerodynamics rather than the cycle technology around which the C1 was based. The weight of the vehicle increased to over , far more than Sinclair's desired specification. By March 1983, Sinclair and Wood Rogers had decided to stop the C1 programme.Dale, p. 155 Wood Rogers comments that Ogle were convinced that the C1 would be a flop, telling Sinclair that it would not be fast enough, that its drivers would get wet when it rained and that the battery was not good enough.