Sinclair C5

Sinclair C5
Sinclair C5 with high vis mast.jpg
Manufacturer Sinclair Vehicles
Production 1985
Assembly Merthyr Tydfil, Wales
Body and chassis
Class Battery electric vehicle
Layout Tricycle
Electric motor 250 W (0.34 hp)
Battery 12 V lead-acid battery
Range 20 miles (32 km)
Wheelbase 1,304 mm (51.3 in)
Length 1,744 mm (68.7 in)
Width 744 mm (29.3 in)
Height 795 mm (31.3 in)
Kerb weight 30 kg (66 lb) without battery, approx. 45 kg (99 lb) with battery

The Sinclair C5 is a small one-person battery electric vehicle, technically an "electrically assisted pedal cycle". [1] It was the culmination of Sir 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". [2]

Sinclair had become one of the UK's best-known millionaires, and earned a knighthood, on the back of the highly successful Sinclair Research range of home computers in the early 1980s. He hoped to repeat his success in the electric vehicle market, which he saw as ripe for a new approach. The C5 emerged from an earlier project to produce a Renault Twizy-style 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 in the event the planned development of the followup C10 and C15 electric cars never got further than the drawing board.

On 10 January 1985, the C5 was unveiled at a glitzy launch event but it received a less than enthusiastic reception from 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 15 miles per hour (24 km/h), 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 became known as "one of the great marketing bombs of postwar British industry" [3] and a "notorious ... example of failure". [4] Despite its commercial 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 £5,000, compared to the original retail value of £399. Enthusiasts have established owners' clubs and some have modified their vehicles substantially, adding monster wheels, jet engines, and high-powered electric motors to propel their C5s at speeds of up to 150 miles per hour (240 km/h).


C5 with the left side of the body shell removed, showing the pedals, chassis, drive chain, battery, and electric motor
C5 seen from the rear, showing the driver's cockpit and the open luggage compartment at the rear

The C5 is made predominately of polypropylene, measuring 174.4 cm (68.7 in) long, 74.4 cm (29.3 in) wide, and 79.5 cm (31.3 in) high. It weighs approximately 30 kg (66 lb) without a battery and 45 kg (99 lb) with one. [5] The chassis consists of a single Y-shaped steel component with a cross-section of about 5.5 cm (2.2 in) by 4 cm (1.6 in) [6] The vehicle has three wheels, one of 317 mm (12.5 in) diameter at the front and two of 406 mm (16.0 in) at the rear. [5]

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 15 miles per hour (24 km/h). At the rear of the vehicle is a small luggage compartment with a capacity of 28 litres (1 cu ft). [5] 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. [7]

The C5 is powered by a 12-volt lead-acid electric battery which drives a motor with a continuous rating of 250 watts and a maximum speed of 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. [6] 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. [8] 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. [6]

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 20 miles (32 km). [6] 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. [9]

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. [10] 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. [11]