At the Olympia Show of 1919 Riley introduced an entirely new model, the Riley 11/40 10.8hp, developed to enable production to be more straightforward than before. By 1925 the highly successful 11/40 model was upgraded to 11.9hp with an enlarged engine of 1645cc by increasing the bore from 65.8mm to 69mm, retaining the same 110mm long stroke, thereby raising the sturdy detachable-head side-valve engines output from 35bhp at 3,200rpm to 42bhp at 3,600rpm. A bigger chassis and front wheel brakes were introduced from 1925. A wide iety of factory body styles were offered, often made by Midland Motor Body, another Riley family firm, and a number of cars were exported in chassis form, particularly to the Antipodes where demand proved strong.