Why do modern cars come with up to 10-Speed automatic transmissions, yet we still only have 6-speed manual transmissions?

Question

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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Answer 1

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.