Interesting mpg displayed on Electronic Traffic Speed Monitor

Speed doesn't drive the odometer, scangauge or factory.

What is there about the workings of a speedometer and odometer that makes you think it would be anomalous for them to be calibrated differently? Considering the potential manufacturers liabilities from any inadequacies, which way would you expect them to make any errors.

The past several cars I have had have all had odometers that were accurate within 1%. Speedometers have varied from dead on to 6% fast.

Most people here who have accurately checked their odometer and speedometer have found the odometers to be quite accurate and the speedometers invariable optimistic.

 

And invariably optimistic (which is based on distance traveled) fuel consumption display? It seems the common denominator is defining a mile slightly less than actual, which would cause (a) displayed speed to be high, (b) displayed fuel economy to be high, and (c) displayed miles traveled to be high.

The only thing that militates towards your assertion the odometer is (more) accurate (and not optimistic) is that when assessing actual MPG using the odometer reading and fuel consumed, the calculated value is consistently less than the display. However, I've heard this has more to do with fuel metering measurement accuracy than the odometer.

If not, the fact that other manufacturers have essentially admitted they calibrate odometers to be off by up to 5% makes me ask why Toyota couldn't be doing the same thing.

I'm not trying to be argumentative, but please provide data and not merely anecdotes. (And no, I don't practice law in any area that makes this more than an academic discussion.)

So I'll ask the question: has anyone here in fact used "speedometer" calibration markers on a freeway (that test over a distance of more than 5-6 miles) to confirm the ODOmeter reading shows 10 miles traveled in 10 minutes while the speedometer shows a constant 60 miles per hour? If so, then I'll concur with your conclusions and appreciate the education.

Best,
Bob.

 

You can determine speed error more accurately with a GPS. A GPS will be accurate to 0.1 to 0.5 mph depending on the GPS and atmospheric conditions. You can see how accurate GPS speed is by standing still with one. They will usually read 0 mph or within a small fraction of 0 mph. That doesn't sound like much of an achievement until you consider that the 0 mph is calculated based on your relative velocity compared to 3 or more satellites moving at approximately 18,000 mph and you are moving at about 750 mph relative to the center of the Earth. Then the GPS tells you how fast you are moving relative to the spot of the Earth you are standing on. It's a handy way to check your GPS velocity accuracy.

For the odometer reading, you can also use GPS if you are traveling on a relatively straight road but mile markers that are there to check odometers give many people a warmer fuzzier feeling. The reason for using a GPS for speed instead of the mile markers is that it is difficult to hold speed constant within a fraction of a mph over a distance of 5 or more miles. There is no need to make the odometer check at exactly 60 mph, although you shouldn't make it at a wildly different speed if that is the speed you are checking the speedometer at.

If you have a handheld GPS or can borrow one, give it a try.:rockon:

 

Its is so your warranty runs out faster.

 

Today I noticed that my GPS read about .5 mph too fast and the Scangauge read 2 mph too slow but then would jump up to the speedometer speed then back down again repeatedly. My new tires are larger in diameter than the OEM tires. I used to run 2mph too fast consistently with the OEM tires. I kind of like being accurate now. It also partially explains some of my mpg loss with the larger wheels.

 

Our Prius is the one of the first to be built, I believe
in April 2009.

I noticed that on radar trailers for traffic control when
the speedometer is at 35 MPH the radar trailer displays
a speed of 34 MPH.

The odometer is quite accurate. On the mesured 5 mile marker post on Interstate 5 near Olympia, Washington, at about MP #99, its
just a hair off.

In 5 miles actual the odometer would measure about 4.95 miles or so which is better than the other way. Now, I wish the MPG guage read the same way. It has been pretty much consitently off by 2.5-3.5 mpg since day one and we now have over 52,000 miles on our prius.

If the guage reads, lets say 55 mpg, than the true calculated mpg will be from 51 to 53 mpg, somewhere in that range.

A couple of times the MPG guage acutally read lower than calculated but I believe it could be a glitch in the pump shut off or another factor.

alfon