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Old 10-03-2009
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Question about MPG calculation

I have heard from a few people on here that if you have bigger tires you need to use a certain calculation to figure out your actual MPG.

For example, I would take the number of miles I got the tank and multiple it 1.09. That would compensate my new tires size. I would then divide by the number of gallons like usual.

My question is, is this legit or fake?
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Old 10-03-2009
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full tank

drive x ammount of miles.

fill up agian

take miles divided by gallons = miles per gallon.
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Old 10-03-2009
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Quote:
Originally Posted by Vonhanson View Post
full tank

drive x ammount of miles.

fill up agian

take miles divided by gallons = miles per gallon.
I know how its supposed to work. Its an easy equation.

I want to know if larger tires change this.
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Old 10-03-2009
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Quote:
Originally Posted by Vonhanson View Post
full tank

drive x ammount of miles.

fill up agian

take miles divided by gallons = miles per gallon.
Yeah i think what he was askin, was because he has a different tire size on the truck the speedo is off which would make the clock turn at a different rate then the stocker size.

As for conversion i am not sure.
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Old 10-03-2009
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Yeah, you just have to know how far off your speedo is. Get a GPS and go 50mph according to your speedo, and whatever the difference is multiply that by two and thats how far off it is. Mine was 15% off before I got 4.10s so when I calculated MPG I'd multiply my trip miles by 1.15
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Old 10-03-2009
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Yes, the larger tires throw off the odometer so you need to figure out how much the difference is.
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Old 10-03-2009
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have seen an article in an offroad mag that has a chart for you to run the numbers....
I will try and find it, I know its still in the house, havn't cleaned the magazine rack in awhile....
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Old 10-03-2009
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u got it right. mine is for every 1 mile im actually going 1.2
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Old 10-04-2009
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So if this is the case then my odometer is off by .09.

So say my truck since 0 miles has had 295/75/16 tires on it. Then lets say it has 100,000k on it now. In reality it would have 109,000K on it?
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Old 10-04-2009
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bump
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Old 10-04-2009
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Hmm i want to know the answer to this
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Old 10-04-2009
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OK heres the forumla take the difference in your old diameter tire and your new size tire. I.e...stock tire aprox 29 " tall, new tire 35" tall. 35/12=1.2. so for each 1 mile multiply by 1.2. so for every 100 miles on the odometer youve really gone 120. hope this helps
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Old 10-04-2009
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Quote:
Originally Posted by mlw20lu View Post
OK heres the forumla take the difference in your old diameter tire and your new size tire. I.e...stock tire aprox 29 " tall, new tire 35" tall. 35/12=1.2. so for each 1 mile multiply by 1.2. so for every 100 miles on the odometer youve really gone 120. hope this helps
You mean 35/29=1.2
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Old 10-04-2009
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here's the easy way:
Tire Size Calculator - tire & wheel plus sizing

enter in stock tire size, enter new tire size, they tell you the difference.
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Old 10-04-2009
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Jake. There are several ways to do this. The web site above is good if you have large tires. I like this one myself.

Tire size calculator (Works best with tires under 30" tall.)


Another way to do it is just check your odometer against the mile markers on the sides of most roads. A 10 mile trip will give you a good idea. The further you go the more accurate you'll be. If you drive 10 miles and your odo reads 10.3, your speedo is off by +3%. If it reads 9.7 you're off by -3%. Use whatever system works for you.
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