"JCS" <j.stillings.TakeThisOut@comcast.net> wrote in message
news:FfydnSYxrpf5MwvZnZ2dnUVZ_qWdnZ2d@comcast.com...
> '03 ES300 w/60k miles
> Just replaced all four tires, and the odometer and MPG calculations seem
> to have changed slightly. Originally I recorded 27-28MPG on the highway
> and 21-23 in town. Now coming in at 23-25 and 19-21. Checked a couple of
> fixed routes that I drive frequently, and they are reading shorter
> distances than before.
>
> Asked the dealer to check the speedo and odo when it was last in, and they
> say there are not adjustments for tire size. Didn't check the original
> tires against spec but the new ones are exactly what is called for.
>
> Any thoughts/ideas are appreciated...
> JS
>
The dealer is correct, there are no adjustments for the
speedometer/odometer.
I've never measured tire circumferences, but there are probably variations
in tire circumference between tire makers.
Tire size alone does not explain the differences you are experiencing. The
shorter distances mean that the new tire's diameter is larger so it turns
fewer times for a given distance. Tire diameter will vary about 1/2 inch
over the tire's life due to tread wear. Theoretically, a larger diameter
tire should improve fuel economy.
Different tires will have different effects on fuel economy, as will
different inflation pressures. For improved fuel economy and tire life, I
recommend inflating the tires about 4 or 5 PSI higher than the
manufacturer's recommend tire inflation pressures, although this will result
in a slightly harsher ride.
--
Ray O
(correct punctuation to reply)
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