figuring mileage with larger tires - Ford Powerstroke Diesel Forum
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post #1 of 3 Old 01-23-2009, 02:52 PM Thread Starter
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figuring mileage with larger tires

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

Last edited by daveyburt; 01-23-2009 at 03:00 PM.
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post #2 of 3 Old 01-23-2009, 03:43 PM
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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


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post #3 of 3 Old 01-23-2009, 03:51 PM Thread Starter
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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!
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