ZF’s nine-speed (above) was the world’s first. Now Ford and GM think they can do 10. Image via ZF.
Ever since the first gasoline-powered car went up for sale, cars have nearly unilaterally been sold on the promise of more–more power, speed, luxury, comfort, safety, efficiency, wheels, more everything. In the last decade, there’s been a new boom of more: transmissions with more speeds.
While cars got by for a long time with two, three, or four speeds, today we’ve got the announcement that Ford and GM–mortal enemies in the domestic market–are actually partnering to developing a 10 speed transmission. Is this just more marketing hype aimed at capturing the bicycle nostalgia of aging millennials? Actually, it’s not. As silly as they may sound, 10 (and 11 or 12) speed transmissions are actually useful.
Videos by VICE
A BSFC map measuring the efficiency ranges of a Ford 2.0L Zetec engine.
Read it like a topographic map, the regions with lower numbers mean lower
fuel burn per unit of power (so independent of total power.) For this engine,
the most efficient range is between 1500 and 3000 RPM. Via EcoModder.
You can think of the engine powering your car as a glorified air pump–the more air it moves, the more fuel it can burn, which means more power. But because of physics and myriad mechanical operations that keep an engine running, that relationship isn’t always linear. With every engine, there’s a sweet spot where efficiency–whether for power production or, these days, fuel economy–is maximized.
That’s where a transmission comes in. The transmission connects the engine to the wheels, which makes it one of the most important, and most complicated parts on a car. Because of that complexity, along with weight and packaging constraints, cars for years were equipped with cheap four- and five-speed transmissions.
In the ongoing battle for automakers to balance efficiency improvements with R&D costs, it was for a long time cheaper to make an engine run more efficiently than try to cram a few more gears into an already-crowded transmission.
Still, having more gears is going to make your engine’s work easier, which saves gas. Like your bike, having more gears in a transmission means your engine can spend more of its time in its theoretical sweet spot, resulting in better acceleration, better gas mileage, or both.
But only in the past couple decades has engine technology reached the high water mark where it makes sense to spend R&D cash working on adding gears to transmissions, and then figuring out how to make them cheap enough for consumers to afford. Five years ago, a six-speed sedan was still novel. Now, as federal fuel mileage standards increase and consumers still demand a whole lot of power to match their rising MPG numbers, the gear count marches on.
The gains are still slight. Compared to, say, a two-speed transmission, where an engine is rarely in its optimal range, a 10-speed is a vast improvement. Compared to a six-speed, there’s less of a difference. But there’s still a difference, even if comes with huge development costs–huge enough for Ford and GM to try to share them, in any case.
So why not have infinite gears to keep the engine permanently in its most efficient zone? That’s the idea behind CVTs or continuously-variable transmissions, which use a band running through a pair of sliding cones instead of gears to give an unlimited number of ratios. (Yes, the video above is from Nissan, but it does a great job of explaining how CVTs work, and why adding gear ratios can boost efficiency.)
The only problem there is that many consumers don’t like CVTs at all. Unlike a regular automatic transmission, CVTs don’t shift, which means you never hear the “bwahhhhh *kck* bwahhhhh” of an engine revving through the gears as you get on the freeway. Unfounded or not, people also generally don’t like the idea that their gears have been replaced by a chain spinning in some grooves. So even if they’re potentially more efficient, CVTs weird people out.
Which means automakers are left trying to shove more gears into their gearboxes. Ten years ago, a 10-speed car sounded insane, but now they’re on the way, and eight- and nine-speed cars are relatively easy to find. Will we ever have a 15-speed? Well, maybe. Semi-trucks have up to 18 speeds in their all-important quest to always maximize efficiency, and if an automaker ever figures out how to fit that many gears into a car-sized transmission (a rather difficult task), I’m sure it will end up in showrooms.
