Does the tachometer serve any practical purpose?

Dear Car Talk

Dear Car Talk | Dec 01, 1991

Dear Tom and Ray:

My 1991 Infiniti G20 is the first car I've ever owned with a tachometer. The owner's manual tells me to shift gears on the basis of speed, not on the basis of revolutions per minute. That being the case, does the tachometer serve any practical purpose?

TOM: Of course it serves a practical purpose, Dale. Ever since digital clocks became popular, manufacturers were left with a big round hole in the dashboard where the old analog clock used to be. We heard that they wanted to put a hologram of Wayne Newton in there, but negotiations broke down at the last minute. So at the eleventh hour, they had a meeting, and decided a tachometer would fill the spot.

RAY: Actually, Dale, if you have a car with a manual transmission, the tachometer does serve a couple of pseudo-practical purposes. One is to tell you where the "red line" is. That's the engine speed at which the engine will turn back into individual auto parts. But if you drive reasonably, you'll never get anywhere near the red line.

TOM: Race car drivers use the tachometer to tell them when the engine reaches the peak of its power output. So if your goal is to accelerate as fast as possible, you should learn to use a tachometer that way. You should also stay out of my neighborhood, especially when my kids are outside playing.

RAY: For the rest of us--those who don't drive like knuckleheads--the tachometer just isn't necessary. Just shift at approximately the speeds recommended in your owner's manual (and don't be too finicky about it). Also, you should ad?just those shift points for road or driving conditions. For example, if you're climbing a hill, or accelerating onto a highway, you'd want to stay in the lower gears longer.

TOM: Of course, if you have an automatic transmission, you would think that tachometers are completely irrelevant, because the transmission shifts whenever it wants to. And for the most part, you'd be absolutely right. The only exceptions are cars like the Lexus LS 400 and Infiniti Q45. We finally figured out why they have tachometers, and it has to do with how quiet they are. Seeing the tachometer at 1000 RPM instead of 0 is the only way to know that the car is running.

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