For a while there, it seemed as though automatic transmissions would be gaining an extra gear every few years ad infinitum. ZF began building eight-speed transmissions for Chrysler in 2009, and shortly thereafter began work on a nine-speed automatic. Soon after this, Hyundai announced plans to build a ten-speed transmission. Now Ford and GM are working jointly on their own ten-speed transmission. It seemed like it had become somewhat of a transmission arms race until ZF’s American representative told reporters that the efforts to cram more than nine gears into a transmission has more to do with marketing than it does with any actual advantage the extra gears might offer.
Now, according to a report in Automotive News Europe, ZF’s CEO Stefan Sommer has elaborated on why his company is stopping at nine. “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 said, pointing out that adding additional gears would come with a disadvantage in weight and complexity, which would cancel out any benefits.
The advantage of extra gears thus far has been to allow for earlier upshifts and lower revs while cruising at highway speeds, thus improving fuel economy. More gears has tended to be better so far, but it was always obvious that it would have to end somewhere. There does seem to be some disagreement about where that end is,however, and ZF is the first transmission maker to draw a line. In explaining this line, Sommer pointed out that there is now only an 11 percent fuel economy difference between the most advanced automatic transmissions today and a theoretically perfect automatic transmission. His belief is that any narrowing of that gap won’t be achieved by the addition of more gears.
Porsche famously produced the world’s first seven-speed manual transmission for the new 911, but here the number of gears is limited somewhat by the complexity it adds to the shift gate, a problem which automatic transmissions don’t suffer from. This is significant because manual transmissions have been the more fuel-efficient choice for decades, but with recent improvements in automatic transmission technology, they have overtaken manuals in fuel conservation ability. We can probably expect some more improvements in the future, but as Sommer pointed out, we will be hitting a wall very soon.