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I installed a 2.5" BB lift and 35" tires on my 2008 JK Unlimited, I used to get around 20mpg on the highway and now only get around 14-15mpg (I KNOW, changing tires always drops your gas mileage down! :bawling:). I currently still have the stock 3.73 gears in the rear but am wondering if there was a better ratio to run to help out. I am not much at figuring up ratios, but I can change some gears if I need to. Unfortunately, the Jeep is more of a daily driver than it is an off-roader. :mad:
I read in a couple forums that adjusting the ratio to match the current tire size might help with mileage. :confused:

I am open for ideas and help.
 
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Just a quick question. When calculating your new mileage are you taking into account that your odometer (and speedometer) is reading incorrectly because of the larger tire size and that the mileage calculated by the computer is also inaccurate?
 

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True... I have not taken mine to the dealer to have the computer recalibrated for the larger tires. I will have that done and then re-evaluate it. I have read (looking at tables with gears and tires) that it would be better to move to 4.56 gears (avg about the same as stock) to give it back some of that mileage.

Thanks for the info.
 

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If you do a lot of flat highway driving, your gas mileage could improve with bigger tires. When I had 32" tires on my Range Rover I got better MPG on flat highways but worse on hilly terrain. Putting on larger tires is similar to adding overdrive, the problem is it takes more to get going so city MPG suffers greatly as does driving a lot of hills.
 

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I installed a 2.5" BB lift and 35" tires on my 2008 JK Unlimited, I used to get around 20mpg on the highway and now only get around 14-15mpg (I KNOW, changing tires always drops your gas mileage down! :bawling:). I currently still have the stock 3.73 gears in the rear but am wondering if there was a better ratio to run to help out. I am not much at figuring up ratios, but I can change some gears if I need to. Unfortunately, the Jeep is more of a daily driver than it is an off-roader. :mad:
I read in a couple forums that adjusting the ratio to match the current tire size might help with mileage. :confused:

I am open for ideas and help.
Eh, pretty much every combination we've had so far has produced crappy gas mileage...you can only do so much with gearing. You are after all adding alot of air drag, and heavy tires.


first jeep
auto, 4.10's, 35's = 10-12mpg
auto, 4.88's, 35's = 12-13mpg

second jeep
6spd, 3.21's, 37's = too far off to really even drive
6spd, 4.88's, 37's = 12-13mpg
 
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