Toyota Prius: Deviaton ODO meter

"Carpe Diem" <tx> wrote in message
newsTcSg.97546$telenet-ops.be... 
Would you mind telling us how you performed these measurements? I'm
presuming the deviation is from a calibrated standard.

"Bill" <now> schreef in bericht
news:com... 
I don't know how the situation is in the US, but where I live (in Belgium)
there are milestones (is that the correct word?) along the highway (big ones
each kilometer, small ones each 100 meter). So its very easy to calibrate,
assuming that the milestones are placed in the right place...
But as I said : I did the test on different highways, invariably with the
same result.

"Carpe Diem" <tx> wrote in message
news:4pdSg.97597$telenet-ops.be... 
I've a few years experience with precision measurement equipment. First,
you have to know the accuracy of the odometer used to place those markers.
Then, you have to eliminate any human factors such as the time it takes you
to move your eyes from the mile marker to your odometer unless you came to a
full stop at each marker and corrected for parallax.

The diameter of your tires diminishes by about 3/4" as the tread wears down
and there are differences in the diameter between brands of the same stated
size. Compared to tire wear, inflating the tires from 36 psi to 40 psi
isn't going to make anywhere near the difference you will experience from
tread wear. An honest manufacturer would calibrate the odometer to the
diameter of the tire they ship the car with adjusted for 50% tread wear.
There would be an error from the beginning of the tire's life, offset by the
error at the end.

> I've a few years experience with precision measurement equipment. First, 
The car is new ; tires have less than 2000 miles.
Anyway, 4 to 5% seems high to me..
Did anyone do the same test? With what result?

"Carpe Diem" <tx> wrote in message
news:lRdSg.97636$telenet-ops.be... 
The outside diameter of my tires is roughly 25" 4% of that is roughly 1".
Your speedometer should be roughly 2% off with no wear. Now, did you come
to a full stop at each marker? Does your odometer increment in tenths of a
mile? Mine does not hence I would have to see the miles digit increment
exactly as I crossed the starting marker.

I'm asking these question because I'm looking for the other 2%.

"Bill" <now> schreef in bericht
news:com... 
First of all, in Belgium the odometer works with kilometers instead of
miles, but this doesn't make any difference, of course.
In fact, I did not use the odometer (which indeed doesn't have increments of
tenths of a km) but the TripA meter (which DOES have increments of tenths of
a km).
I did NOT come to a full stop at each marker ; this is a bit dangerous on a
highway, isn't it? But each time I waited until the marker passes the very
same "point" (I do not find a better word) of the car, from my point of view
(I hope my English language is good enough to exactly express what I
mean...).
And I repeat : I asked the question because I hoped that other owners had
the same experience (i.e. : approximately the same deviation).

"Carpe Diem" <tx> wrote in message
news:FffSg.97769$telenet-ops.be... 
Under these circumstances, and with new tires, I'm surprised you were within
4 or 5 percent. I could perform this test using our mile markers however I
couldn't turn my head quickly and consistently from the marker to the trip
meter and at traffic speeds this alone would taint my results.

I'm thinking a much more accurate calculation could be made over 10 or 100
miles/km. I'll try this the next time I'm on the interstate highway.

I'm not too surprised...odometers were not really intended to accurately
measure distance, but rather to serve as a common unit for measuring vehicle
usage. Think about a mechanical odometer--because the least significant
digit moves, it's difficult to say when you are at a specific point, so it's
tough to calibrate it. As a result, it really can't be used to make an
accurate measurement of distance, and certainly the precision of the
measurement is poor as well.

A digital odometer only implies more precision, but its precision is
actually lower than a mechanical odometer because you can't estimate the
fractions of a mile like you can with a rolling digit (this applies whether
you are talking about an integer mile or a 0.1 mile type display).

I assume, based on the number of significant figures in your measurement,
that you did this over a fairly large distance (like 1000 miles, otherwise,
the last few digits are meaningless). Are you converting from kilometers as
well? That could introduce a fixed error into the calculation depending on
how many digits you use in the calculation.

- Doug


"Carpe Diem" <tx> wrote in message
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