The overhead-valve (25) Sheerline and its Princess companion were to continue the line after the Second World War; however, by the 1930s Austin had lost its aristocratic cachet, having become well known for its Twelves and Sevens.

[4] The deceptively potent four-cylinder Twenty found fame at Brooklands both in private hands and with works drivers Lou Kings and Arthur Waite (Herbert Austin's Australian son-in-law and competitions manager).

[4] Before the First World War, Austin had produced a range of expensive cars, including a 3.6-litre 20 hp car but, influenced by the manufacturing philosophy of Henry Ford, Herbert Austin decided that the future was in mass-producing a single model and chose the 20 hp class.

The Longbridge plant had been considerably enlarged for wartime production, and it was there that the company had a base to put the theory into practice now with the capacity to manufacture 150 cars a week.

[4] Perhaps hoping to help, The Times published a long item at the beginning of June 1920 in which they professed admiration for Austin's enterprise in launching on the British market "a car made on American lines".

[6] "However it is true the car is an excellent hill-climber, runs very quietly, accelerates rapidly and has very good steering.

[6] Summing up, the motoring correspondent suggested that "if pains were taken to damp out engine vibration and a slightly higher price set which would allow more 'spit and polish' ... Austin will do a lasting service to the country and their shareholders".

As an advance on pre-war practice, the engine was directly bolted to the four-speed centre-change gearbox, which drove the rear wheels through an open propeller shaft.

The chassis, based on that of the Hudson, was conventional, with semi-elliptic leaf springs on all wheels and rigid axles front and rear.

A 75 mph Sports variant was added in 1921 with a modified higher-compression engine and wire wheels, but it was very expensive, and only around 23 were sold.

Effective 4 April 1923 in response to harsh market conditions but in public attributed to improved facilities for manufacture and lower cost of materials and labour, prices were reduced to the following:[9] The car that was destined to succeed the Twenty, the six-cylinder 20/6, was announced at the October 1926 London Motor Show[13] with production really starting in early 1928, and until 1930 the two different engines were sold alongside each other, but 1929 would be the last year of full production for what was now called the 20/4.

[10] Reported refinements for the 1929 Motor Show included: chromium-plated exterior fittings, Triplex glass, improved (dome type) "mud wings (front mudguards) and new gas (sic) and ignition control levers "neatly placed above the steering wheel".

Other minor improvements included: illuminated semaphore direction indicators, side deflectors for the front door windows and an interior visor, a lockable metal spare wheel cover.

The occasional seats fold away neatly, give enough support to the back and knee and toe room is well arranged.

Equipment includes such fittings as: two interior lights, five blinds, parcel net and ventilator in the roof, bag pockets on the doors.

The half-elliptical springs have Silentbloc shackle bushes and zinc interleaves and are damped by hydraulic shock absorbers.

The spare wire wheel and its tyre are now carried in the boot and the luggage platform on the door can be swivelled to one side.

The Jackall four-wheel hydraulic jacks, workable from inside the car, will raise all four wheels at once or the front and back ones in pairs.

[25][27] Other improvements across the board included: pistol-grip handbrakes under the dashboard, increased luggage accommodation, piston-type hydraulic shock absorbers, more accessible batteries and a quick-filling petrol tank.

[25] Rigid axles back and front supported low-periodicity positively lubricated half-elliptical springs with hydraulic shock absorbers and jacks.

The design with the alloy cylinder head having proved so successful on the Austin Fourteen it would now be applied across the range.

It included a higher compression ratio, "upwards of 6 : 1" which in combination with the larger inlet valves improved fuel consumption and power output.

Pressure lubrication was supplied to the tappets, coolant temperature was controlled by thermostat and coil ignition was provided with automatic advance.

The occasional seats give reasonable comfort, the doorways behind are wide, the boot has two good-sized fitted suitcases with the spare wheel below and its platform is designed to take 1½ cwt 168 lb (76 kg) of extra luggage.

[26] The new engine has the extra refinement in running noticeable in the other new Austin units and shows much improvement on the former Twenty.