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of 100 Westminster Bridge Road, London
Cars built in south-east London
1892 J. D. Roots of London built a strange two-stroke tricycle which also ran on "heavy oil": this led to the production of motor cars from 1896 in partnership with Cuthbert Venables trading as Roots and Venables, but output remained small. 
It was capable of 15 mph and the engine was a single-cylinder two-stroke operating on the 'Day' cycle, with crankcase compression. It was water-cooled and hung upside-down behind the rear axle, which it drove by bevel gears. The frame tubes circulated the the cooling water and it had a single front wheel.
Although the De Dion-Bouton tricycle was more famous, this pre-dated it.
1895 An early primitive motor vehicle named the 'Petrocar' was produced. It was powered by a 2.5 hp 500 rpm single-cylinder engine and was a three-wheel vehicle. 
1896 May 22nd. 'Yesterday a motor-car passed southwards through Redhill, creating no small excitement in its passage through the town. It was the Root’s Petro-car, and was proceeding from Purley through Redhill, southwards. All who saw it must have been struck with the perfect ease with which it was propelled and guided on its way. A proof of the great safety this special type of horseless carriage was furnished between Purley and Merstham. The rubber tyre of one of the wheels came off, but the carriage was instantly stopped without the slightest shock to those within it. The tyre was fastened with string, and the carriage proceeded on its way. This Petro-car, which was made Messrs. Roots and Venables, is driven means of petroleum. The great advantage which is claimed for it is the ease with which oil can be obtained; it can bought in every town and village in the country, while it is much cheaper* and less dangerous than spirit. The inventors of the Petro-car claim that the type is the only one in existence which uses oil as a means of propulsion, all others use spirit. Messrs. Roots and Venables have, we understand, been commissioned supply one of the London Omnibus Companies with of their 5 h.p. motors.”'
1896 November. 'THIS vehicle, which we illustrate as manufactured by Messrs. Roots and Venables, of 100, Westminster Bridge Road, is built with a strong angle steel frame, carrying the oil motor of 2.5- horse-power at the back, together with the exhaust box and small water-tank, The power is transmitted from the crank-shaft of the engine to a counter-shaft by means of belts working on various-sized pulleys, which counter-shaft again transmits the power to the axle of the carriage by a pinion and toothed wheel. This two-speed gear runs the carriage at ten or four miles an hour as desired. In the front of the carriage the larger water-tank is fixed out of sight beneath the feet of the riders. The carriage steers remarkably easy, and is fitted with two brakes, one on the front wheel and the other on a drum on the main axle. Sufficient oil is carried for a run of 27 miles in the tank, but more can be easily placed under the seat. The tyres are of solid indiarubber dovetailed into steel rims. The oil used is common American Tea Rose or Royal Daylight, price 5 1/2d. per gallon. The specific gravity of this oil is from .8 upwards. Consequently it: is quite safe to use, and must be distinguished from the gasoline or benzoline used by most other carriages, particularly those at present running in France.'
1897 April. Details of the Petrocar.
1897 They became the Roots Oil Motor and Motor Car Co
1901 May. Latter detailing attempted sabotage of the car at the Automobile Show.
1902 April. Description of their 4-hp 'Runabout'.
1902 May. Details of the 2.5-hp oil car.
1902 they were taken over by Armstrong Whitworth
1897. THE ROOTS' PETROCAR. 
The Roots' Petrocar, the newest type of which is illustrated on this page, uses ordinary oil in place of the benzoline spirit generally employed in the French and other motor vehicles. This spirit is stated to be two and a half times the running cost of oil, and cannot be obtained as readily in villages as ordinary oil, as used in the Roots' Motor, and it is calculated about 10 per cent. more power is obtained from a pint of oil than from a pint of benzoline. This motor is therefore not a benzoline motor but a true oil-motor, with a flashing-point above 73 degrees F. (Abel's flash test).
The Roots' Petrocar is constructed with a double steel-tube frame, round which the jacket water is pumped by the motor, which so cools the water that about half the usual quantity is carried. The motor, of three horse-power, is fixed at the back of the frame and gears directly by chain on to the axle of the vehicle from the counter-shaft of the motor, which runs at half the motor speed. The valves are also operated by this shaft. The motor runs at 500 revolutions per minute.
While pneumatic tyres are fixed to the carriage illustrated, Messrs. Roots and Venables intend in the future to fit solid rubber tyres to all Petrocar wheels. The weight of the car, as shown, is 5.5 cwt. It will travel at about 11 miles an hour for level roads and 4.75 miles for hills.
Many projecting parts and all nuts are nickel-plated, while the steel-tube frame is enamelled. Messrs. Roots and Venables two or three years ago, foreseeing what was coming, protected as a trade mark the words "Petrocar" and "Petrocycle". They exhibited, even as far back as 1893, a vehicle motor using oil.
The firm are making their motors up to 11 brake horsepower, and amongst their special patterns are the following Petrocars:—
The running cost of the 1.5 horse-power motor is about ld. for each 10 miles run; and of the 3 horse-power motor, 2d. for each 10 miles run, and any kerosine or paraffin of 73 degrees F. to 150 degrees F. (Abel's flash test) can be used.
Just as we go to press, we understand that Messrs. Roots and Venables have had the honour of receiving a solicitor's letter on behalf of the British Motor Syndicate, stating it has been determined to take proceedings against them for infringement of the Syndicate's patent rights. We can only hope, in conjunction with Messrs. Roots and Venables, that this threat is meant seriously, as that firm welcomes being able to have the opportunity of thrashing out and finally settling the claims of the British Motor Syndicate to dictate terms to all British users of motor-cars. So far from Messrs. Roots and Venables' patent being an infringement of any patent owned by the Syndicate, we understand that the firm claims that the facts are absolutely reversed, and that they have substantial cause of action for infringement of their patents. This opinion is, we believe, backed up by eminent counsel's opinion upon the subject, and we trust that for the general good of all those interested in the motor-car industry, the pretensions of the British Motor Syndicate to the ownership of so-called "master patents" may be disposed of once and for all. Whatever the result, a legal decision would be welcomed by everybody and clear the way for increased efforts on the part of engineers to place all kinds of motor vehicles on the market. At present the industry is suffering by reason of a number of engineering firms, who have a natural dislike to complicated legal actions, holding bark until a decision has been arrived at one way or the other.