4 Oct 2009

Why do cars with automatic transmissions have tachometers?

This [unedited] guest post is by a student in my EEP100 class (background post).
Please praise/critique/comment on its economic quality and importance to you.

Jeffrey Hartmeier says:

Tachometers display engine speed via revolutions per minute and are useful in manual transmissions to determine shift points and avoid redlining. However, automatic transmissions have set shift points and will not allow the driver to redline the engine so using the tachometer is unnecessary. But if tachometers are useless in cars with automatic transmissions, why are they still included in such cars?

One possibility is that cars are produced on an assembly line and designed for the masses. Although the manual transmission option makes up only a small portion of the car market, the necessity of a tachometer in a manual car leaves the car producer with two options:
  1. Make two designs of dashboards with two separate production lines, or
  2. include tachometers on all cars.
The cost of putting the tachometer in all cars is outweighed by the savings of having only one design and production line for both manual and automatic cars.

Another possibility is that tachometers can be helpful in identifying or diagnosing engine or transmission problems in both manual and automatic cars. Tachometers also can help set the most efficient speed when using cruise control so that the RPM stay low. Still another possibility is that consumers simply enjoy watching the RPM increase when they step on the gas or when the gears shift.

Bottom Line: Tachometers are present in cars with automatic transmissions due to producer attempts to limit costs/designs and consumer demand.


  1. Actually, cars went decades with manual transmissions and no tachometers. It's pretty easy to hear the right time to shift. And the computerized diagnostic equipment nowadays does not need a gauge on the instrument panel to indicate issues with the drivetrain.

    Seems to me that tachometers are mostly a marketing item designed to give the illusion of sportiness to the vehicle.

  2. Speculation isn't evidence. Other possible explanations for this observation exist as well. It's a good subject for an economic analysis - but the author hasn't presented one.

  3. It's the ultimate affectation.

  4. Some automatic transmission have a "manu-matic" mode that allows them to be shifted manually, so a tach can be useful in that case. Modern engines have such a broad power band, and modern transmissions have so many more gears than the old three-on-the-tree in most cases it really is just a boy-racer affectation. But staring at the needle is a fun way to pass the time until your next text message comes in.

  5. well in my case where I drag race (which an auto tranny helps with consistent times) a tach is usefull because you dont usally start in drive..you start in 1st and you have controll when you shift through second into drive (3rd, 4th, and OD)

  6. Better question...

    Why no tach on manual shifets? I've noticed that such usually do not have a tach standard.r So... you want a tach when it would actually be useful? Oh, you'll have to pay for that.

    Bottom line: Usual stupid marketing crap! (Nuke Madison Ave.)

  7. As listed above, tacks make the dash more impressive, however if it fails, expect to pay over $350.00 in order to get it repaired. Mine works when it feels like, therefore since it is not really needed and all other components operate correctly, screw it.

  8. I wouldn't buy a car without a Tachometer, even if it had an automatic transmission. However I believe it shouldn't be as large as the speedometer. The tach should be one of the smaller gauges off to side of the speedometer. The 2017 Mazda 6 has a beautifully designed analog gauge cluster. They placed the tach in the right spot.


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