Kind of ramdom
JK Enthusiast
Joined: Nov 2010
Posts: 344
Likes: 1
From: NH
You will not get better mpg with 4.56 gears. I have 33s (28.8" actual) with factory 3.73 gears and 6 speed. Mpg is about 17 on flat highway travel. I think 3.73 is the best setup upto 33" tires. If you go to 35s, you'll probably want to regear to compensate for power loss but dot expect better mpg.
If you increase tire size and keep 3.21 gears you'll be running at lower rpm and may see mpg increase slightly but not enough to be happy with power loss (you won't be using 6th on large hills anyway).
Jeeps have the aerodynamics of a brick. Recommend you stick to 3.21 and lighten up on the skinny peddle if you're looking to get a bit better mpg. Nothing you can do about loss of power and mpg on big hills short of supercharging or swapping for a hemi.
If you increase tire size and keep 3.21 gears you'll be running at lower rpm and may see mpg increase slightly but not enough to be happy with power loss (you won't be using 6th on large hills anyway).
Jeeps have the aerodynamics of a brick. Recommend you stick to 3.21 and lighten up on the skinny peddle if you're looking to get a bit better mpg. Nothing you can do about loss of power and mpg on big hills short of supercharging or swapping for a hemi.
JK Freak
Joined: Jan 2011
Posts: 933
Likes: 0
From: El Paso, TX
If you ever plan on going to 35's and no bigger then that go with 4.56. 4.88 and 35's are too much for highway driving 70 mph I'm running at almost 3k. Yea it's great off road and around town but not really for long trips if I wasn't going with 37's next tire upgrade I would probably consider regearing again to 4.56. I have a 6speed and I did have 3.21's stock
JK Enthusiast
Joined: Jul 2010
Posts: 457
Likes: 0
From: BC
Word. I agree fully I am rocking 4.88's on a manual unlimited with 316/75r16's if 75 is a speed you rock often then I would say 4.88's are too much gear if gas mileage is a factor. I get about 14 mpg combined city and highway. 4.88's work for me cause I am in Canada and live no where near a freeway. So with speed limits at 60mph 4.88s are fine but 75 I think would be up there in rpms. This again is mostly true if you do lots of highway and want good mpg's.