Why do modern cars come with up to 10-Speed automatic transmissions, yet we still only have 6-speed manual transmissions?
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The added complexity for the driver to have to deal with more gears to shift through doesn’t result in enough benefit to be worth the effort. Most higher speed autos are done so for fuel efficiency purposes but that’s not so much the case when driver’s choosing when to shift.
I’d imagine that you either have to shift gears 10 times to get to top speed and 10 times again when you get to a red light.
Or you can skip shift a couple gears at a time but risk the car having a jerking motion.
Automatic transmissions work by chaining multiple planetary gearsets in different ways, this is quite complicated to explain, but basically it means that they don’t really need ho have 10 actual gears like a manual, the gear ratios are created by combing the same gears in different ways
You ask a question that presumes to contain accurate information.
I instead could ask “Why do modern semi-trucks have up to eighteen manual gears, when a Shelby GT500 Mustang only has a seven-speed manual transmission?”
There are manual transmission setups with a large number of gears.
You’ll really only see them in tractors and freight trucks.
These setups usually include two or more transmissions in series.
A setup with two 4 speed transmissions will provide 16 different combinations, then a third only for forwards/reverse totals a full 32 possible combinations.
Designs like these are for equipment that really need a lot of power at low speeds.
The average car simply doesn’t need this. It doesn’t take nearly as much to get it moving, and cars typically don’t do any ridiculous amounts of work.
Even in my own car, I don’t use all the gears. They just aren’t necessary.
More often than not, I only use 4 out of the 6 gears, and that’s plenty of range.
As for automatic transmissions, you’ll often see them using planetary gears.
Now, planetary gears are quite special. Instead of selecting a single gear, they can select a combination of gears.
The gears are each equipped with their own clutches that can switch independently to create various ratios. It doesn’t take as many planetary gears to provide a large number of combinations.
This would be very difficult for humans to operate. It’s not so difficult for a computer.
With this in mind, an automatic transmission with more gears can have ratios that are quite close together. It’s almost like taking a 6-speed transmission and adding a new gear between each that’s halfway from one to the next.
These closer ratios make the shifting less aggressive. Instead of jumping from a ratio of 0.75 to 1.25, it can shift from 0.75 to 1, then 1.25, and the acceleration is going to feel much smoother.
These extra gears wouldn’t help make things smoother in a manual transmission quite as much. The aggressiveness or smoothness of shifting is based on people’s experience level and driving style and how well they can operate the balance between the clutch and gas, regardless of gear ratios.
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