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Discussion Starter · #1 ·
has anyone here (preferably with an automatic) ever noticed better highway mileage after swapping to larger tires? i do a lot of highway driving every day for work and im at 3000rpm at around 70 and i think if i swap on my 285's it might lower my highway rpms a bit and help save me a little fuel. i know the tires are a bit wider and heavier but i dont know how badly that will affect my mpg's compared to lowering my rpm's.
 

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It really depends on how you drive. Remember your speedometer will be reading slow. My gas mileage stayed about the same going from stock 28.5" street tires to 32" MT tires.
 

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I feel that until the tires get so big that the dam air and force the engine to push against more resistance, then tire size will prolly give about the same gas mileage.

From stock to the 31s and 32s I've had on my Amigo (5-speed) I cannot say that I've seen any noticeable improvement - but the tach is running slower at a given road speed.
 

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I experienced a slight increase. Went from 19.5 to 20.0 when I went from 245/70/16 to 265/75/16.

To get the correction factor, Google it. There are several sites that let you input both tires sizes and get a percentage difference. So, take that percentage and add to the miles driven total.

For example, if your correction factor is 6%, take the miles driven on the odometer and multiply by 1.06.

I used a GPS to get the actual distances when I tested the change.

I also employ a conservative driving style, rarely hitting 70 on the freeway and shifting at low RPMs.

Good luck.
 

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If your main only purpose for the bigger tires is to help save mpg, don't bother.....seriously.

I run 32" tires, up from 29" tires stock on my 97 rodeo automatic V6, I've ran 285's in the past as well.

Doesn't matter what I run on this truck I've always averaged the same mpg, 17-18mpg city; 20-24mpg highway.

Personally, unless you're going to regear, 32"s are about as big of a tire you want mated to the automatic. 33's are ok, but if you pull a lot of mountains, tow, etc....you'll learn to hate 33's real quick.

They may lower your rpm's, but they can rob a lot of pickup/take off power too.
 

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i went with 33's knowing im regearing...I agree you do lose alot of pickup and power.....im running a 10ply Nitto trail grappler.....and my gas mileage has gone down noticeably from 29's and power has taken a hit...but im also carrying alot of extra pounds from my 255/55/18s to my 285/65/18's....

if you dont weant to lose power plan on regearing....cuse even with my current motor setup im not happy with the loss of power with all that extra tire.... 4.30's going in for now, from 4.10(was an auto trans) def getting 4.56!!!!!
 

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I think there are to many variables to know for sure without trying it, and letting us know the results of course.

Another thing most people don't realize or know is that tire design and tread pattern can have a big effect on mileage. I went from a straight ribbed Michelin tire on my Dodge pickup to their LTX M/S and lost 1 mpg.
 

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SurferJoe said:
...but the tach is running slower at a given road speed.
Did you adjust your speedometer to correct for the different size tires?

Jack
 

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My last tank was 21mpg with 32" MT tires. Previous best tank was 22mpg with stock tires. It still averages 19-20mpg mixed driving.
 

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Discussion Starter · #10 ·
since i already have the 285's, im just going to mount them and find out after i recalibrate. ill post my findings as soon as theyre on.
 

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I am not really sure as I have not owned the Passport very long to get a long term average but I think I am down a mpg or two with the TreadWrights. Treadwrights are also pretty heavy so that can have to do with it. I am averaging 17ish with little highway driving and lots of hills.
 
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