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.