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Deviaton ODO meter

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Posted by Carpe Diem on September 26, 2006, 4:50 pm

I noticed a deviation of the ODO meter (NOT the speed...).
Actually, 1 mile on the ODO meter is in reality 1.0465 miles.
I did the measurements more than once and always find the same deviation
(between 4 and 5%).
Is this normal? Is it because the tires have a higher pressure than what
Toyota recommends?

Posted by Bill on September 26, 2006, 5:08 pm

Would you mind telling us how you performed these measurements?  I'm
presuming the deviation is from a calibrated standard.

Posted by Carpe Diem on September 26, 2006, 5:26 pm

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.

Posted by Bill on September 26, 2006, 5:46 pm

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.

Posted by Carpe Diem on September 26, 2006, 5:56 pm

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?

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