familytime

Try slowing down,we get 17-18 highway on 37's

JK yeti

Whaaaaaatttt?!!! How.. I'm on 35's, 4" lift and 4.10 gears and I averaged 15mpg at 65-70 mph

CombatDiver

In Utah I was getting 20-24mpg regularly, now I live in Houston I get 12-13mpg. My wife's Toyota Camry Hybrid has also suffered a a similar 1/4 to 1/3 drop in efficiency. I am seriously considering a complete overhaul of the air intake to exhaust to try to obtain better fuel efficiency but I'm afraid like mentioned there's more to it than simply the vehicle and what wheels (while certainly a major component it's just not all there is).

Sent from my DROID RAZR using Tapatalk

twotonevert

I get 15mpg, just a little better when I run 100% gas. Not more than 16 though.

TheEngineer13

What is 100% gas? or rather, what would you run otherwise?

twotonevert

Around here, most of what you will find has an ethanol blend, usually 10%. The station closest to my house is non-ethanol, or 100% gas. My jeep runs a lot better without ethanol, but it is usually 15 to 20 cents higher than ethanol blends at other stations. My wifes car actually gets another 5mpg better on 100% gas. Wish the jeep did. LOL

SKTN Rubi

I am guessing he uses a fuel additive to achieve the better mpg calculations.

EDIT: never mind he just posted his answer I was wrong.

TheEngineer13

Things that can effect your gas mileage.

1. Type of fuel you are using. Depending on your location, a lot of areas have switched over to "winter blend". This fuel has more additives to prevent things like jelling during lower temps. These fuels are notorious for lower MPGs.

2. Non calibrated ECU. Adding larger tires changes the number of axle rotations in a mile, if the ecu is not re-calibrated for the change in size, this will effect your odometer, speedometer, and displayed MPGs. The factory tire is a 32.06"; your 305/65/17 are roughly 32.67" your difference in speed you be roughly 2 to 3 mph at 100mph. The calculated MPGs would be off by such a small percentage (depending on your driving style and use) that you may be off .1 - .3 MPG.

3. Rotational mass. This is the weight of all the parts which have to be rotated by the engine. More rotational mass = more required torque. To produce more torque you use more fuel. I will not go into static vs. kinetic energy because that's middle school physics, other than to say, if you can keep the rotating mass in more of a kinetic state you will increase your MPG. Factory wheels and tires are somewhere between 64 lbs and 72 lbs depending on which wheels and tires you had stock. Your tires alone are 65 lbs a piece add in the weight of what ever wheels you may have and chances are you are somewhere between 90 - 100 lbs per tire; or a difference of roughly 30 lbs unsprung rotational mass, per tire.

4. Your driving style. This plays the largest factor in MPGs. How you accelerate, how you stop, even the way you make a turn will effect your MPGs. Jeeps aren't fast. If you drive your Jeep and expect to keep up with everyone else from a stop, you can kiss your MPG goodbye. My biggest testament to the way you drive is my own Jeep. its a factory fresh 14' 6MT with 3.73s. I've seen as high as 22mpgs, I keep it between 65 and 70 on the highway, and I don't care about keep up with everyone else on the road. I accelerate at my own pace, shift in the "eco" range, and slow at a nominal pace. In traffic I avoid the stop and go by falling back and keeping a steady pace. Sure it sounds like I drive like a bitch, I don't care, I get 20+ MPG and I still take the Jeep off road and get it all dirty.

5. Lastly, as you now have an automatic, verify that this is actually shifting into 5th gear. Your 5th gear is your overdrive gear, or in other words, a gear ratio that is far lower than the other four in order to keep your RPMs lower at highway cruising speeds. As your new tires now weigh more, your engine must now work harder to maintain the same speed. As your transmission is now controlled by a computer, the programming my not allow the car to get into 5th. You can fix this with a tuner which will allow you to adjust your shift points.

TheEngineer13

Okay. Yes, ethanol = bad (in many cases). Its not cost effective, and it gets horrible mpgs, but it also give you more power. I built a rally car to run on E85 because it was a race car so MPGs were not a concern and we could get about 415 hp out of the engine which would produce about 360 hp on normal gas. But thats besides the point, if you can, stay away from ethanol for your normal street driven cars.

JKUon37s

I don't even see how this is possible. I'm on 37's with stock gearing, 4.10's, for now and I'm averaging 12. Highway at 65-70 mph I can squeak out 14. It is hilly and windy where I live so that May have something to do with it but you must only drive downhill with a tailwind.