Introduced in October 1908, the Ford Model T had a simple 100'' wheelbase and a chassis which was both lightweight and durable, and continued in production with little basic change until May 1927, with over 15 million sold. Robust to the point of indestructability and built with top-grade vanadium steel, the Ford Model T used a two-speed planetary transmission. Developments included electric lighting in 1915, a switch from brass to a black-finished radiator in 1916, and optional electric starting from 1919. By the mid-Twenties competition prompted the introduction of balloon tyres, the option of wire wheels, and the availability of a range of different colours.