The nine-speed transmission could represent the end of the battle to add more gears, according to ZF CEO Stefan Sommer.
He described nine speeds as being the “natural limit” taking into account that by adding more gears it will increase complexity and weight that can’t be offset by fuel efficiency gains. In an interview given to Automobilwoche, Sommer said that “there is no hard line, but you have to consider the law of diminishing returns. The question is whether adding even more gears makes sense.”
Three years ago ZF started manufacturing its 8-speed gearbox designed for cars and light trucks powered by longitudinal engines. ZF says that compared to a 6-speed transmission it provides 11 percent improved fuel economy. In 2013 the company will start making a 9-speed gearbox in the United States and they expect sales gains since the Chrysler Group will adopt these gearboxes for high-volume models. This new gearbox will bring a 16 percent increase in fuel efficiency compared to a 6-speed unit.
Despite this "natural limit", in the future we’ll get to see ten-speed gearboxes since Hyundai has already confirmed they are developing one, while GM teamed up with Ford to jointly create 9- and 10-speed automatic transmissions.