The Austin 18-24 is a large 5-litre luxury motor-car that was produced by the British manufacturer Austin. Despite the name, its successive engines rated around 30 horsepower for tax purposes and the pundits of the day regarded it as really a 30–40. It was launched in 1907 with the 25-30's 5.3-litre engine and in Austin's catalogue replaced the 15-20, of which only four were made. The next year it used the 15-20's 4.4-litre engine.