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Most people know that for old or even somewhat old cars, manual transmissions are more efficient. Recently automatic cars have become almost as efficient or even as efficient as manuals.

I was recently reading an article by Road & Track magazine that was comparing different sports cars, and it mentioned the fuel efficiencies of the manual versions versus the automatic versions, and actually listed the automatics as being more fuel efficient than manuals by about 2 mpg.

Are automatic transmissions now really more efficient than manuals? Is this for all cars or just high-performance cars?

If autos are now more fuel efficient than manuals then how have they managed to make this so?

Zaid
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user180969
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3 Answers3

24

Traditionally...

The major drawbacks of automatic transmissions were:

  • parasitic losses in the torque converter, something which manual transmissions don't have.

  • fewer gears, so a given engine was more likely to be in its sweet spot with a 5-speed manual than a 4-speed automatic during regular operation.

  • gear selection logic which was inferior to well-trained human drivers

Over time...

Transmission manufacturers have worked out ways to reduce the impact of these drawbacks, including:

  • Direct-drive to lock out the torque converter to prevent losses
  • Adding more gears helps keep the engine in the right rev range for optimal fuel economy when the conditions allow for it (8-speeds are quite commonplace nowadays, even 10-speeds)
  • Quicker and more intelligent gear-selection logic that can handle a wide variety of driving scenarios.

For further reading: see this reddit comment, which does a good job of summarizing the answer to this question.

Zaid
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20

A lot of new automatic transmissions (e.g. Volkswagen DSG) arent actually auto transmissions, at least not in the traditional sense. They have a normal computer-controlled dry clutch (well two actually) so they do not need to move around a lot of transmission fluid like traditional automatic transmissions do. Also they have a lot of gears (7, 8 or even 9 speeds like the Mercedes 9G-Tronic) and upshift quickly when cruising to have better gas mileage. That part explains why modern automatic transmissions often are even more fuel efficient than manual transmissions.

MadMarky
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With a greater number of gears in the autobox and with a lock-up function called more frequently for the fluid flywheel.

Then add a better computer based control system for moving between gears : improved algorithm and faster change control.

Solar Mike
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