The nine-speed transmission might be where the race to add gears ends, ZF Friedrichshafen CEO Stefan Sommer said, according to a report by Automotive News Europe.

He deemed nine speeds the “natural limit” because surpassing that number would add weight and complexity that cannot be offset by gains in fuel efficiency.

“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,” he told the Automobilwoche Congress in Berlin. Automobilwoche is Automotive News Europe’s German sister publication.

ZF is expecting big sales gains for next year because Chrysler Group is adopting the German company’s eight- and nine-speed transmissions (pictured above) for mass-market models.

There have been reports of General Motors’ and Ford’s collaboration on nine- and 10-speed transmissions, as well as of Hyundai developing a 10-speed gearbox.

In an earlier Automotive News report, ZF North America president Julio Caspari hinted that a “Can-you-top-this?” cog race may be driven by marketing considerations rather than fuel economy, explaining that there is only an 11% gap between the most efficient transmissions today and a theoretically perfect gearbox.

Next year, ZF will start production of its 9HP nine-speeder at a Greenville, South Carolina plant, while Chrysler will manufacture that and the existing ZF eight-speeder under license at its Kokomo, Indiana plant.

ZF says the nine-speed transmission, which is designed for transverse-mounted engines, is up to 16% more efficient than a conventional six-speed automatic.