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I upgraded to 456's and 35's and my mpg has taken a nose dive. This morning was my first long drive about 100 mile and I went through almost a 1/2 a tank of gas. The team that did the gearing did provide a flashcal as they needed to program the new gear ratio.

Are there other things that need to be done to improve mpg with 35's. The odd thing is that on this trip I used my cruise control at 65 as I break in the gears, so it wasn't a led foot causing the lack of fuel economy.
 

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This isn't going to end well. But I'll bite.

Large heavy tires and associated mods aren't inline with good highway (or any) mileage....not sure what you expected to happen...

At 65 I get 17ish mpg *IIRC* with my 315's. (3.6L, automatic, 4.10's). With my mixed driving I get 15.


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With the lower gears your RPMs are going up within the gears. And then you are going to be cruising at highway speeds at a higher RPM. I have 4.88 and 35s and I make about 230 before my light comes. I hit half right around 120

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4.88 gears with 35's here and the best mpg is running 65mph - generally around 17mpg. Around town 13mpg. There was a thread where everyone posted their average mpg and I charted it. Many variables other than gears and tires come into play. Driving habits, flat or hilly, weight, etc..
 

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Using cruise control or driving steady state is not really good until the gears are broken in. Heat cycles is what you want and varying speeds of driving but no hammering the throttle. And until you have broken in the gears MPG means nothing.
 

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The basic rule of thumb is the more aerodynamic a vehicle is the better the MPG. OK, we can toss that one out with the Jeep, besides, we are comparing the same vehicle.

Next, the taller the tire the better the MPG, however the wider the tire the worse the MPG. The best mileage is achieved by the pizza cutters, tall and skinny. Ever look at the wheels on a Bonneville speed vehicle? Tall, very, very skinny with flush wheel covers.

Next, the taller the gearing, the worse the MPG. And of course with new gears, you have the break in period of higher resistance in the gears, hence worse gas mileage.
 

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On relatively flat ground at 65-70mph with no wind I can knock down high 19's... sometimes a 20.0...5.13's, 35x12.50 BFG KM2's at 36psi... 6spd.
Take tire pressure down, and/or increase speed and things start getting worse.
Around town I can get mid 17's if I really pay attention... If I think I'm in a hurry that quickly drops to low 15's.
Up in the mountains with long stretches of 6% or better grades I get mid 17's at the same 65-70mph.
I've got stubby front bumper with winch, a tonne of armor and the rear bumper/tire carrier... but no roof rack or light bars.
I run 87octane and around here it's got a lot of ethanol mixed in which does not help.
 

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wow mike I'm jealous, 5.13's and have several sets of 37s and one set of 35s. i can't get anywhere over 16mph on the highway. Im not sure on my mph as never recalibrated but I'm basing mine off highway speed of 3000-3200 rpm which should be around 65/70mph
mine is a 2011 so 3.8 motor.
 

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I have a Sport with the stock 16 wheels...I get 20 miles per gallon average. If I put on larger tires and 17 inch wheels, Would that screw up my gas mileage ?
 

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Yes eddie it will , the stock sport on 16s is about the best mpg you can get in a JK.
unless you have a diesel 2.8 liter, then you could go numerically lower gearing but the 3.8 and 3.6 are both really limited as to engine mods short of swapping motors.

in general if you have tall skinny tires the mpg will be better than fatter tires.
 

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I have a Sport with the stock 16 wheels...I get 20 miles per gallon average. If I put on larger tires and 17 inch wheels, Would that screw up my gas mileage ?
Maybe not as much as you may think. Yes, the best gas mileage is with tall skinny tires, but you have short skinny tires. P225/75R16 tires which are 8.9" wide and 29.4 inches tall. Going to 17 inch wheels and 255/75R17 tires (10" wide and 32" tall) can give you the better gas mileage or worse depending on the tire design. Don't forget your computer will have to be reflashed for the change in tire size so the engine computer is correct as well as your odometer and speedometer.

If you go with the BFG Mud Terrains which have large open blocks (the better to throw off mud) as well as softer compound, the rolling resistance is greater than on an AT style tire. My 2015 Sahara with P255/70R18 tires (also 10" wide and 32" tall) over the course of 19,000 miles had an overall average of 19.6 MPG. Note that I am retired and do not live in a city environment so most of my miles were on the highway, but there is also some trailer pulling miles in there as well. It also had 3.21 gears which I believe your Sport would have.
 

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wow mike I'm jealous, 5.13's and have several sets of 37s and one set of 35s. i can't get anywhere over 16mph on the highway. Im not sure on my mph as never recalibrated but I'm basing mine off highway speed of 3000-3200 rpm which should be around 65/70mph
mine is a 2011 so 3.8 motor.
If you never re-calibrated your mileage is off as well as your speed.
I assume you have a manual trans.
 

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Something to keep in mind is that if you go to a larger diameter tire and adjust your gearing at the same time, say switching to 35's and 4.56 gears, much of the gearing change is simply correcting for the increase in tire size. So, there may not be an increase in rpm's at a given speed cruising down the highway. Going to larger tires will almost always bring with it a reduction in mpg. If you don't adjust your gearing when you go to bigger tires you may see more of a reduction in mpg during city style driving and less of a reduction in highway style driving. That somewhat depends on the terrain you drive and how you drive. Adjusting your gearing when you go to larger tires will typically help your city mpg more than your highway mpg. But that again depends on your highway driving terrain and style (how fast / aggressive you drive).
I don't know why any of this really matters, as a Jeep is never going to get mpg worth getting happy about. They suck at mpg and adding bigger tires will make it suck even more. To me gearing is about either balancing the bigger tires you added to bring it back to where it was or adjusting it to make the Jeep perform better than it did stock.
 

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Crap, i'm going to gear up to 9.30's, looking for 40mpg, freaking awesome, the taller the gearing, the best mpg, who would have thought, only on WF... :drinks:
 

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If MPG matters, you're playing on the wrong team. When you graduate to 35's you get in the 13-16 camp. Start saving up for a 18 with the diesel. The hit you take on your JK plus all the added expenses of a new JL would pay for all the gas you could ever use. We all make choices in life. You chose a JK.
 

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If you never re-calibrated your mileage is off as well as your speed.
I assume you have a manual trans.
YEP its off and its great, odometer registers about 10 percent less miles, for mpg I'm using real math at the pump vs how far i can go . Advantage of a manual over automatic is you don't have to reprogram it.
 

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wow mike I'm jealous, 5.13's and have several sets of 37s and one set of 35s. i can't get anywhere over 16mph on the highway. Im not sure on my mph as never recalibrated but I'm basing mine off highway speed of 3000-3200 rpm which should be around 65/70mph
mine is a 2011 so 3.8 motor.
n/m, I see you have the 6spd.
 
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