OK . . . you've got me wondering here. My truck came with the
31" tires (so the CABS should be set to 689 already right?). I
changed to 32" when the bad-years wore out. I haven't had the
computer flashed or anything. I thought my mileage would only
be off by the difference in percentage of circumference between
the 31" and 32" tires which is like 3.1%. If what I am reading
here is correct, the real difference is 9.3%? I'd appreciate
the confirmation.
Thanks,
JY
--- Ronald Wong <ron-wong@home.com> wrote:
> Nothing to do with trig. Just good ole fashioned geometry.
> The difference
> around the outside of the tire is called the circumference.
> Circumference =
> diameter X pi. The tire revolutions per mile is the number of
> times the
> tire rolls the length of the circumference. If you have a 32"
> tire you are
> right in your calculations. That percentage is a whopping
> 9.3%. The next
> time you calculate your mileage, multiply the mileage your
> odometer says
> you've gone by 9.3% and add that figure to the total because
> that's how far
> you've actually gone. Divide that by the number of gallons of
> gas you used
> for your MPG. This all presumes the dealer flashed your CABS
> to 689.
>
> Ron
> 00 PB SLT QC 4X2 5.9 46RE 3.92 LSD
> For modifications see my DML Profile (URL follows)
> http://www.twistedbits.net/WWWProfile/dakota/Kw9pV1EkFeOYY
>
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