figuring mileage with larger tires

[daveyburt]

so, maybe i'm just completely missing the boat but, let me explain...

if larger tires make my speedo a few miles an hour slower, then my odometer is a little slow as well right?

if this is so, this thing tells me my Speedo Difference is 3.75%
i went from 265/75/16 to 285/75/16 - actual speed 60mph, speedo 57.8mph

then why would i not figure this into my mileage equation?

Example 1:
295.8 odometer miles on 20.5 gallons = 14.42mpg

Example 2:
(295.8 / 20.5) + (14.42 / 3.75) = 18.26mpg

of course we like the 18.39 better ....which one is reality?


just wondering if you all figure this way or not...
to a point, larger tires should give you more mileage (in general driving, not towing) as you're turning a taller gear....no? am i completely screwed up

dave

[SuperCrutyPS]

Here's my take:
Stock (265) tires go around 657 times, the 285's go around 633 times. So when you're Odometer sees a mile you've actually traveled over a phyiscal mile.
So with the 3.75% difference, you would take your miles traveled + variance % = actual miles. 295.8 + 3.75% = 306.9 <--round up a tenth.
Then take the 306.9 miles divided by 20.5 gallons = 14.97mpg

[daveyburt]

hmmm, i see how that makes sense.
figure the miles traveled before dividing by gallons used.

numbers don't lie, unless they're figured wrong.


thx!