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Armstrong Siddeley 30hp
Armstrong Siddeley 1919 Olympia Motor sh

Great emphasis was placed on the desire to bring to the public a lighter and extremely refined motor carriage having good performance, allied to moderate first cost and running expenses. To achieve this end it had been decided to initially concentrate on a single design - a 30HP car, featuring a six cylinder overhead valve engine embodying the use of aluminium in its construction. The use of this material resulted from the experience gained in the manufacturing of the successful Siddeley aircraft engines. Full specifications are listed in the tables below, however it should be noted that the ‘Siddeley Cantilever' type springing and new type disc wheels were worth special mention. Also of importance was mention of the new design of radiator and bonnet.

It was suggested that the price of the Chassis, equipped with - electric lighting and starter set, five lamps, four tyres, step-boards, all wings and dashboard, would be £660.00.


 The cars were first shown in October of 1919 at the London Motor Show which was held at Olympia.  A bare chassis and four types of body were on display. The styles shown were designed and built by the Burlington 'in house' coach builder. The manager, a Mr Inglis, expressed his opinion of the all new Siddeley car when he stated that ''The top hat is always smarter than the bowler.''


The car was equipped with everything that would be expected of a quality carriage and in the case of the enclosed cars interior appointments were somewhat opulent. On the open road the cars could attain 60mph whilst returning 13mpg.

The Engine

The engine which powered this vehicle had a capacity in today's measurement of 4960cc and was constructed of two three cylinder blocks, with individual cylinder heads which incorporated overhead valves, all mounted on a common aluminium crankcase. The crankshaft and the camshaft each had three bearings. The ignition was by magneto which also charged the battery used to power the electric starter and ancillaries.

Armstrong Siddeley Mk I 30hp engine

The Mk I 30hp engine

Introduced for the 1925 season the Mk II  30hp car had a heavily revised version of the Mk I engine having a one piece cylinder block but still retaining two separate cylinder heads. The OHV pushrods were now enclosed in the engine block. From January 1928 the Mk III engine was introduced and was now a true monobloc with one piece cylinder head. All three versions had a bore of 88.9mm and a stroke of 133.4mm and carried an RAC rating of 29.5hp.

Armstrong Siddeley MkII 30hp Engine

The Mk III 30hp engine

The Chassis
Armstrong Siddeley 1920 30hp Chassis

The Mk I 30hp Chassis

The cars were built on a steel chassis, having side members which were at some points 12'' in depth, a wheelbase of 11'3'', track of 4'8'' and an overall length of 16'4'' and one quarter inches. Front suspension was by semi-elliptical springs with cantilevers being used for the rear. The rears were adjustable for height to accommodate differing body weights.


Initially, the lever-arm shock-absorbers were fitted to the rear becoming an optional extra for the front at a later date. Rear wheel braking was normal on the early cars with the addition of front wheel braking becoming available at a later date to give the four wheel braking we expect today.


The car sold well and was attractive to those in the wealthiest sector of society. Having been denied the delight of buying a new car since 1914 they were eager to purchase. There were also many who had benefited from their efforts in war production and could easily afford such a car.

Images from the 1920 Armstrong Siddeley brochure
Armstrong Siddeley 1920 30hp Saloon.jpg

5 Seat Saloon priced at £1,295.

1920 30hp Coupe Saloon 40Kb.jpg

4 Seat Coupe Saloon priced at £1,295.

1920 Armstrong Siddeley 30hp Open Tourer

5 Seat Open Touring Car priced at £1,190.

Armstrong Siddeley 1920 30hp Landaulette

5 Seat Open Drive Landaulette priced at £1,400.

The rolling chassis option was taken up by one particularly notable person in 1928 when HRH the Duke of York, later to become King George the VI, ordered a Mk III 30hp chassis to be sent to an unknown coachbuilder in order to have it equipped as a shootingbrake.

Armstrong Siddeley 30 hpRoyal Shootingbrake
Armostrong Siddeley 1928 30hp Shootingbr

The finished vehicle was delivered to the Duke and Duchess's home, Birkhall on the Balmoral estate in Scotland, where it was used for three years. The rear compartment could accommodate a shooting party of eight people and their equipment.


Though not owned by the present Queen the car was on show, to the delight of the public, for many years in the Royal Motors section of the museum at Sandringham.  At present it is with its owner in America.


The concept of the 30hp car was not a sudden decision. Siddeley in line with other astute businessmen had given thought to the time when peace returned, whenever that might be. As far back as 1917, the car manufacturers in Coventry had gathered together to discuss that while they were busy supplying the war effort the unencumbered Motor Manufacturers of the USA were surging forward with designs and methods of production. Concerns were expressed that the American cars would be in a position to make great inroads into the British market when the war was over whilst the British companies were struggling to restructure.


John Siddeley, ever true to character, then quietly imported a Marmon model 34 car from the USA for close examination. His selection was due to the high reputation which this manufacturer had both at home and as the choice of the French Government.   Later in 1919, he would send his son Ernest Siddeley on a buying mission to America to study styling, materials and production methods.


From this distance it is difficult for us to appreciate the styling changes which were developing in the States. Most of us remember the more flamboyant shapes of the later airflow and chrome days. However, note the rounded edges to the Siddeley car which greatly helped to reduce the bulk of the vehicle and refine the design.

The 30HP was to prove the backbone of the fledgling company throughout the 1920s and even influenced the design of the engine fitted to the Siddeley Special of 1932.                                                                               

More Images of the 30hp
Armstrong Siddeley 30hp Harrods Hire Car

Harrods Department Store, Knightsbridge, London, hired out these cars complete with Chauffeur. Many overseas visitors toured in the UK using this service.

Armstrong Siddeley 1933 30hp.JPG

An image taken from the 1933 sales brochure. These late cars reflect the changes in styling taking place in the early 1930s

Armstrong Siddeley 1920s 30hp open drive

This 1920 Armstrong Siddeley 30hp Open Drive Limousine, now celebrating 100 years, is still roadworthy.

HRH The Duke of York with an Armstrong S

In 1920 Armstrong Siddeley supplied this 30hp Limousine to HRH The Duke of York the future King George VI of United Kingdom

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