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Hey guys, so finally had a chance to get a full tank, and drive a good amount of 99% highway driving and trying to get as accurate number as I can. Only thing I'm having an issue with is compensating for my bigger tires and my speedo not being calibrated for it. Anyone know how to do that?

 

Here's my numbers:

 

Trip meter = 425.8 (has 285/70/17s when speedo is set for 265/75/16s so this is biggest concern)

Used 22.3 gallons of diesel

 

Hand crunching those numbers still comes out to 19mpgs which isn't terrible but pretty sure it's a little different due to tires/speedo being off. Thanks in advance!

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https://tiresize.com/calculator/

285/70/17. 102.7 inches 

265/75/16.  99.4 inches 

63360 inches in a mile

63360÷102.7=616.94 rev/mile

63360÷99.4=637.42 rev/mile

That's 3.21% different 

425.8÷22.3=20.3mpg 

20.3 at 3.21% should be around 19.65 mpg

But I suck at math,  so... 

Edited by Dieselfuture

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Don't even start this method... It does not work. 

 

Grab a GPS and track your mileage/odometer. Do not attempt to calculate mileage from a percent offset it will not come close. But you'll find that if you track with a GPS total distance you numbers are correct.

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Well I know this method won't be the gnats a** accurate, I have no plans on getting a GPS so close enough will work for me as I'm really more just trying to get an idea anyways.

 

Here's what I came up with

 

old tire diameter 31.6

new tire diameter 32.7

 

31.6 / 32.7 = .96 - 1 = .0336 or .035

 

So trip meter showed 425.8 x .035 = 14.9 + 425.8 = 440.7 of 'corrected' trip mileage

 

440.7 / 22.3 would be 19.7mpgs so really not that far off from uncorrected but still nice to know it's a little more accurate. 

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Like with my Quadzilla I run slightly higher (71%) volumetric efficiency percentage from stock (63%). The volumetric setting calibrates your fuel consumption rate. Then I've got my ABS reprogrammed with @Chris O. CCD tool. But there is an offset setting in the vehicle editor setting for speedometer offset. This will calibrate your speed and distance.

 

http://www.obdlink.com/

 

 

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