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Discussion Starter #1
when my commander was completely stock the information center in the instrument cluster was saying i was averaging 11.4 miles per gallon (i have the 3.7 liter V6)....i just put the 20 inch wheels and tires on and it is now saying 14.2 miles per gallon. is this number inaccurate because of the new wheels and tires or did my fuel economy actually improve? the new tires only have a .21 inch larger diameter and .66 inch larger circumference than stock.....
 

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I am not sure if the computer is inaccurate, but larger wheels will not improve your gas mileage. It will probably lower your mpg's since there is more weight to move around. How are you getting 11.4 mpg's with the 3.7L V6? I have the 3.7L and I get 18 in the city and 21 mpg going 75 on the interstate.
 

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When I had my 3.7 I avg 13mpg, mostly because it seems like every 10 ft in this city we have a stop light. He might be seeing improvements because his driving style is not the same as the previous driver.

Now the larger tires cover more area when you drive so you will loose mpg due to the weight and the diameter of the tire. Also your speedo will show slower speeds due to this. So say your doing 55mph according to your speedo, you could be actually doing 65mph.
 

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It is possible you are seeing the significant decrease in rolling resistance street treaded tires provide.
I think a 3mpg difference is a bit of a stretch but I can't say it couldn't happen either.
Regardless, if you are experiencing any increase, lucky you.
Jeep looks cool and cheaper to run as well......bonus!

Rob
 

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The bigger tires will definatley cause the engine to run at a lower RPM than the stock tires ... weather or not that will incrse MPG depends on many factors.

If you did not have the speedomoter adjusted to compensate for the new tires, it is reading incorrect MPG and incorrect MPH

It will be out the percentage difference in the tire's circumference .
 

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Well, agreed,
But he's only .66 larger in overall circumference and .21 taller.
I can't imagine that small a varience causing that much gain in readouts.

Rob
Sorry i din;t check the tire sizes ... So .66 inches?

if it IS getting better milage any real gains could be doubled in error by the computers inacuracy ... maybe the .66 was enough to lower shift poiints across the board??

I agree it should not be anywhere near that much though.
 

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Discussion Starter #9
thanks for the replies guys....according to the tire size calculator posted as a sticky on this site, when im going 60 mph with the stock tires, i would actually be going 59.5on the 20 inch tires, which is a speedometer difference of 0.715% slower.....but yea i cant imagine it gaining that much of a difference either.....but i will try the reset button, i dont know why i didnt think about that beforehand lol
 
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