Why do cars with automatic transmissions have tachometers?

On Sun, 18 Sep 2005 07:52:40 GMT, TLittle said the following in rec.autos.driving...

Often wondered about this myself. If the auto makers just have some bug up their butts that says they *have* to put gauges in the instrument cluster, I can think of several that I would rather have before a tach.

Reply to
Paul.
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They are little more than visual entertainment for virtually all drivers. You can watch the needle move up and down as the automatic transmission shifts itself. For those who are truly bored or need to feel in control a tiptronic type automatic transmission in combination with a tach can provide hours of road-racer-like thrills.

The space could be used more effectively with a good analog clock and a couple of useful gauges like oil pressure and voltage.

Reply to
John S.

While I don't disagree entirely; a tach is not completely useless. When I'm sitting a a light with the stereo up and the car is idling a little rough the tach might indicate that I'm only idling at 400 rpm. If I'm at the same light and the car is idling exceptionally smooth the tach might indicate that the engine has died completely. Until I recently diagnosed a faulty idle speed stepper motor either of these was a regular occurrance.

Reply to
Rick Brandt

I wonder why Audis have such high top gear ratios. At 70 mph in 6th, the engine is running at 2800 rpm.

Reply to
Arif Khokar

Smaller engine, I suspect. What's the capacity? And how many MPG are you getting?

Reply to
223rem

2.7L V6 twin turbo. I get roughly 25 to 26 mpg on average according to the trip computer.
Reply to
Arif Khokar

TLittle writes in article dated Sun, 18 Sep 2005 07:52:40 GMT:

So you can detect a stall at a traffic light without turning the stereo down. :^)

Most automatic transmissions have low-gear settings. It would be a good thing to know when you're at the upper range of one of these.

-- spud_demon -at- thundermaker.net The above may not (yet) represent the opinions of my employer.

Reply to
Spud Demon

My old '87 T-Bird "redlines" at 5000, and the rev limit is factory set to 5500. I'm not kidding.

BUT: I could buy a PROM chip which would crank it up to about 5700 RPM and modify the VE mapping, to give me about 9% more horsepower. Hmmm........

So, what is redline, anyway? 500 RPM before it blows up? :-)

It's kind'a like the torque on Honda motorcycle cylinder head bolts. No torque wrench, or can't get the damn torque wrench in there? No problem! The correct torque is: "a quarter turn before it strips".

Reply to
~^Johnny^~

I thought you were referring to my Enzo. Never mind.

Reply to
~^Johnny^~

Isn't that usually quoted: "Torque it until it strips and then back off a quarter turn"?

:-)

Reply to
Alan Baker

Sun, 18 Sep 2005 07:52:40 GMT:

Yes, most automatic and manual transmissions have a low gear setting.

An automatic transmission takes care of that automatically.

Reply to
John S.

You do know that all auto trannies allow you to shift down, right? -Dave

Reply to
Ted B.

Yes, as do manual transmissions. And your point is......

Reply to
John S.

That RPMs can get awfully darn high when you downshift. While a tachometer isn't absolutely necessary (regardless of transmission), it is useful (regardless of transmission) -Dave

Reply to
Ted B.

But by then, it's too late, you see... ...it's already been stripped! ;->

I'd hate to tell you how they test fuses...

Reply to
~^Johnny^~

haven't read the entire thread but looks like this is the first "correct" answer:

When descending a hill, with the automatic transmission selector lever in low gear, like "L" or "2", the tachometer can be used to insure you do not exceed redline and incur engine damage, which when locked manually in the lower gear is possible.

Reply to
nospampls2002

True for older purely hydro-mechanical transmissions. But name me an automatic transmission currently made that won't upshift at or before redline REGARDLESS of what gear is selected. There are probably a few still out there, but not many.

Reply to
Steve

Please don't take this personally, but if you don't have a good idea what will happen to engine speed when you downshift a tachometer will not do much to solve that problem. If you drop it into an inappropriately low gear the tach will only tell you after the fact that you screwed up and overrevved the engine. Engine noise will tell you roughly the same thing. I would strongly suggest that you just leave the transmission in Drive and let brakes do the work of slowing the car.

Reply to
John S.

If you don't know what will happen prior to moving the shift lever a tachometer won't solve that problem. You would be much better off leaving the car in drive if you can't avoid overrevving an engine by dropping to the next lower gear.

A tach is for the most part low grade visual entertainment - watch the moving needle.

Reply to
John S.

TLittle < snipped-for-privacy@mail.net> writes in article < snipped-for-privacy@mail.net> dated Sun, 18 Sep 2005 07:52:40 GMT: What's the point of the tachometer on a vehicle with an automatic transmission? So you can detect a stall at a traffic light without turning the stereo down. :^)

Seriously, based on my understanding of WHY the tachometer exists, why are there tachs on vehicles with automatic transmissions? Most automatic transmissions have low-gear settings. It would be a good thing to know when you're at the upper range of one of these.

-- spud_demon -at- thundermaker.net The above may not (yet) represent the opinions of my employer.

I offer the following; it hasn't to do with why or when to use a tach with an automatic transmission, but rather why there's a tach in an automobile with an automatic transmission at all.

It's more cost effective for the manufacturer to include a tach in all models where a tach would otherwise be an option.  As I postulate, it's cost effective from the design, manufacturing, procurement, assembly, and all other aspects for the manufacturer, not necessarily the consumer.  All consumers pay a small price for a gauge few will ever use, even those with a manual transmission.

This is especially apparent when you consider the similarities (i.e., cost effectiveness) among models, not only with the gauges, but also the supporting electronics as well.

Similar to, but different than...why are automatic transmissions even offered in certain vehicles, for example: Jeep Wrangler, Corvette, and

4x4 Trucks.  I already know the answer, but it still makes me laugh a bit when I pull up next to a "sports car" and look down and see an automatic shifter.

Agave

Salud, dinero, amor y tiempo para disfrutarlos

01 F350 PSD Crew Dually
Reply to
Agave

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