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Tried2Live said:
Just out of curiosity, how have all of you guys corrected your speedometers/odometers with the bigger tires? Flash the computer or what?
If they haven't....what the are posting for mpg is wrong, in a good way. They are getting better gas mileage than they think.

a gps reference would be a good way to tell how far off the speedo is. By taking the precentage it is off and multiplying and adding the differance to what they got on that tank of gas...then calculate the new mpg. it should look like this -

all numbers and figures are just to illustrate my point.

350 miles to the tank with big tires and a 20 gallon tank

Mpg before correction - 350/20 = 17.5mpg

Speedo is off by 10%

correction - 350 x .10 = 35, 35+350 = 385

385/20 = 19.25 - corrected mpg (roughly)
 

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Tried2Live said:
Just out of curiosity, how have all of you guys corrected your speedometers/odometers with the bigger tires? Flash the computer or what?
From what some people have said here, the speedo is off from the factory and the taller tires actually correct the speedo. A few months ago I drove by one of those radar guns that display your speed and my truck was going the same speed that was displayed.
 

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Blackenedsrt-4 said:
If they haven't....what the are posting for mpg is wrong, in a good way. They are getting better gas mileage than they think.

a gps reference would be a good way to tell how far off the speedo is. By taking the precentage it is off and multiplying and adding the differance to what they got on that tank of gas...then calculate the new mpg. it should look like this -

all numbers and figures are just to illustrate my point.

350 miles to the tank with big tires and a 20 gallon tank

Mpg before correction - 350/20 = 17.5mpg

Speedo is off by 10%

correction - 350 x .10 = 35, 35+350 = 385

385/20 = 19.25 - corrected mpg (roughly)

Yeah, that's why I asked.


As for the factory speedo being off, I have the in-dash nav unit and a handheld Garmin GPS, and they both are within 1mph of the factory speedo. Not saying it's not possible that other peoples' speedometers are a little off, but I can't see them being off so much that tires that much bigger will fix things.
 

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Stupid is stupid does
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265-70-16's 2.7L 5 speed 17.5 mpg :disappoin
 
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