Pet Peeve: Tachometers

[ls1mike]

Originally Posted By: Hokiefyd
To put it another way, common convention for gauge labeling is:

[gauge reading equals] "label"

So, [speedometer gauge reading equals] MPH. Nobody puts "= MPH" on a speedometer; the leading "=" is implied.

[gauge reading equals] x1000 r/min is not correct. It's telling you that the gauge is reading equals 1000 times the r/min which is not accurate. That's why it annoys me; it's inconsistent with other gauges.

I just read it as, RPM is the gauge label
Then 1000 X the number. Either way if it were, take a number, say 3 rpm x 1000 That is 3000 RPM by my GM tachs.

 

[Quattro Pete]

Originally Posted By: javacontour
Actually, isn't the one in the picture INCORRECT.


It says RPM/10. Don't gauges list the unit of measurement?

So if the needle reads 10 then according to the units listed on the gauge, is it turning 1 RPM?

No. The designation on this gauge is RPM/100. What this is telling you is that the gauge takes the actual RPM and displays it as if it were divided by 100. Example, it takes 3000 RPM and it displays it as 30. How did they get to 30? They took 3000 (RPM) and divided it by 100.

 

[TallPaul]

I really like this aftermarket tach I had in my old F150 4.9L

What irritates me is tachs without a redline. Many Fords over the years have had a 0-6000 rpm tach with no redline.
Can only figure they don't want to stock more than one gauge face.

 

[eljefino]

Originally Posted By: ls1mike


Funny story...My ex wife's grandma had a 2.8 Cadillac Cimarron.
Here is the dash...

She drove from Long Island to upstate NY when she first purchased it. When she got to the house, she told my father-in-law and I that the car wouldn't go over 30 mph and it used too much gas. We were puzzled so took it for a ride.


That's a canadian speedo. Look closely at the little blue MPH numbers inside.

Having owned a 1982 cimarron, I can say the speedo only goes up to 85 MPH, as did every car sold in the US at the time... a fuel economy thing.

Also note the yellow zone on the tach starting at "55"; remember, we had to circle or otherwise emphasise 55 MPH per law back then.

 

[ls1mike]

Originally Posted By: javacontour
Grandma may get confused and take that 30 as speed as we've seen described here.

Originally Posted By: Hokiefyd

Which is always awesome. I remember the conversation after we drove the Cadillac. "Grandma, you were driving by RPM or revolutions per minumte"
Grandma "What? Who gives a bleep about that. Where the bleep is the speedo?"
Nothing like an 82 year old 100lbs woman coming unglued.

 

[ls1mike]

Originally Posted By: eljefino
Originally Posted By: ls1mike


Funny story...My ex wife's grandma had a 2.8 Cadillac Cimarron.
Here is the dash...

She drove from Long Island to upstate NY when she first purchased it. When she got to the house, she told my father-in-law and I that the car wouldn't go over 30 mph and it used too much gas. We were puzzled so took it for a ride.


That's a canadian speedo. Look closely at the little blue MPH numbers inside.

Having owned a 1982 cimarron, I can say the speedo only goes up to 85 MPH, as did every car sold in the US at the time... a fuel economy thing.

Also note the yellow zone on the tach starting at "55"; remember, we had to circle or otherwise emphasise 55 MPH per law back then.

True, I just need it for the tach.

 

[Quattro Pete]

Originally Posted By: eljefino
Also note the yellow zone on the tach starting at "55"; remember, we had to circle or otherwise emphasise 55 MPH per law back then.

But why was it denoted on the tach? You'd never come anywhere close to 5500 rpm if you were to stay at 55 mph.

 

[ls1mike]

Originally Posted By: Quattro Pete
Originally Posted By: eljefino
Also note the yellow zone on the tach starting at "55"; remember, we had to circle or otherwise emphasise 55 MPH per law back then.

But why was it denoted on the tach? You'd never come anywhere close to 5500 rpm if you were to stay at 55 mph.


That is pre redline for a 2.8 55 being 5500 rpm and 60 being 6000 rpm which is redline.

55 was red, yellow, or stood out on the speedo back then. I screwed up and posted a Canadian Dash. KPH.

86 Cimarron state side, what dear old grandma had.

 

[opus1]

The Cobalt and Dakota both use single-digit numbers with "RPMx1000" on the face. The Ranger doesn't have a tach. Not sure about the Sonata and it's too hot outside for me to go check.

 

[davebarnum]

Google went outside and checked for you. You have a tach which displays "x1000 rpm."

 

[ls1mike]

Originally Posted By: davebarnum

Google went outside and checked for you. You have a tach which displays "x1000 rpm."

Oh, that was awesome, thanks for the laugh.

 

[Tegger]

Originally Posted By: Hokiefyd
Originally Posted By: Tegger
My Honda's tach is labeled x1000r/min, which is correct.
The Toyota tachs I've seen all say x1000RPM, which is correct.
My old Mazda's tach said x1000rpm, which is correct.

None of those is correct. Your tachometer labels tell you that the indicated numbers are x1000 the actual engine speed. If your tach shows 2, then what the gauge is saying is 2 is x1000 the actual RPM. It's telling you that the RPM is 0.002 revolutions per minute, which is not correct.

I guess it depends on how you interpret the numbers.

I'm interpreting the label at the bottom of the tach as a formula with a variable at the front of it, and with the "x" being a multiplication symbol. So if my tach reads 3, then I would apply this formula based on the label on the tach: 3 x 1000 revolutions per minute. And that's 3000 rpm, of course.

Your original question gave the label as "RPM x 1000", which is clearly wrong, since the purpose of the formula is to determine the RPM in the first place, not to multiply (unknown) RPM by 1000. And I can't ever remember seeing a tach with "RPM x 1000" on it.

 

[fdcg27]

This is your 530i?
Looks exactly like the display of my '95 318i, including the speedo.
Like a 318i would ever see more than 120 mph or so.
BMW must have used the same cluster on all of their cars for a number of years.
I like the "mpg" gauge.
What does it really measure?
Instaneous fuel flow (which the engine management computer could give)?

 

[DBMaster]

It might be interesting if a company decided to report RPM's financial statement style. In other words, have single digits on the tachometer display and have "1000's" printed at the bottom instead of "X 1000."

 

[ls1mike]

Originally Posted By: Tegger

And I can't ever remember seeing a tach with "RPM x 1000" on it.


Here it is again...

 

[ls1mike]

1/1000 of engine speed.
Ok I get that.

but 1 is = to 1000 rpm on that tachs scale. That is all they are doing. It is like calibrating gauges for the Navy.
Gauges on there are lets say for 700, they are labeled 70 x 10.
It is to just clarify the scale.


It is a display of revolutions of the motor. I expect that when my needle is pointing at 2 the motor is spinning at 2000 rpm. They make it nice and easy for everyone.

 

[Hokiefyd]

Yeah, I'm used to domestic tachs, and many of them do say RPM x 1000. Apparently, Ferrari does this as well.

Tegger, I understand what you're saying. "Engine speed is [gauge indicated] x1000 r/min." Much like "vehicle speed is [gauge indicated] MPH." I yield to that.

The way Chevy did it with the Chevelle is clearer to me, double-digits not withstanding. If Mike's Pontiac's tach (above) said "RPM / 1000", that would make more sense to me. Because that's literally what it is. That "6" at redline is indeed not RPM x 1000. It's really RPM / 1000.

Obviously, we all know what it means. The engineer in me hones in on things like this, though.

Oh well. Interesting to see all the various tachometer styles out there...

 

[Quattro Pete]

Originally Posted By: fdcg27
I like the "mpg" gauge.
What does it really measure?
Instaneous fuel flow (which the engine management computer could give)?

That's my understanding... it's based on fuel injector pulses which the ECU measures/collects, in relation to speed/distance.

 

[Hokiefyd]

Originally Posted By: ls1mike
You guys are making this too hard.


I know. It's just a tick I have, pardon the pun.

Some people will say to "unthaw" the meat, or to "unloosen" the knot. Some people don't even notice, but I catch stuff like that. Gauge labeling is car-guy grammar to me. It's like an air gauge that might be labeled in "pounds" instead of "PSI". We all know what "pounds" would mean, but "PSI" would be more accurate. I'm a geek like that.

Actually, I'm a geek all over, but...

 

[01rangerxl]

Originally Posted By: TallPaul
I really like this aftermarket tach I had in my old F150 4.9L

What irritates me is tachs without a redline. Many Fords over the years have had a 0-6000 rpm tach with no redline.
Can only figure they don't want to stock more than one gauge face.


Most Ford engines "redline" past 6000 RPM, which is why it is not displayed on the tach. Your truck is electronically limited to 6250 RPM. It would need to be turning faster than that to do any damage or make the valves float.

My pushrod 4.0 Explorer had the same gauge cluster, but did have a redline on the tach at I think 4500 or 5000 RPM.