After the First World War Holbrook is offered a position within the company as general manager and work began on designing a new range. They launched the model SD (Spring Drive). This 550cc single cylinder machine had a large diameter spring rear shock absorber, a clutch and chain drive through a three speed gearbox. This had a 500cc four valve engine and the first Triumph to use overhead valves set at 90 degrees apart producing 20bhp. The engine was designed by fuel technologist Harry Recardo using an aluminium piston and a machined steel cylinder. The bike became known as the Riccy in his honour.

In 1923 the company produced its first bike with an oil pump powered from the engine. Until then the rider had to pump the oil around by hand. Triumph launches the mass produced model P with a 500cc engine and three speed gearbox. It sold for £42 17s 6p and was produced at a rate of 1,000 per week. Production now occupies half a million square feet and some three thousand people make 30,000 machines per year, many for export. Sales catalogues were produced in ten different languages including Japanese. In 1928 Triumph changes the flat style petrol tank to a saddle style. They also changed the colour scheme from a traditional green to black with gold pinstripes or pale blue panels on a black background.Foot operated gear shifters replaced hand operated items on 650cc twin models.

In 1937 the 500cc Speed Twin was introduced at a price of £75. It was a roaring success with a top speed of 90mph, its design was considered to be the iconic British motorcycle. Tiger 100 twin announced. It is a sporty version of the Speed Twin reaching 100mph. In 1940 production of bikes for the civilian market is halted to produce for the military. Production was up to 300 machines per week for military use, when on November 14th the Priory Street works was destroyed by German bombers. Production restarts in temporary facilities in Warwick making 310cc and 500cc side valve machines as well as generators for the RAF. In 1942 production moves to a brand new purpose built factory on the geographic centre of Britain in Meriden