lopezv123

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.

Charlie K.

CParks has 3.21 and 35's with a 6 speed and gets around 17mpg I have 4.10's with 37's and get 16 to 19 depending on how I drive. I use 6th alot and he only uses up to 5th. I would think with 32's and a 6 speed 3.21 would be fine, if your foot was a little lighter on the skinny pedal. Like the above posts, if your going to stay with 32's I would save the money for regearing and upgrade something else. Even if you got an extra 1 to 2 mpg how long would it take to recoup your investment? If you look at the gear chart you are at the low end of min. but the extra 3-500 rpm's with the regear and use of 6th would probably lower your mpg. This is all guesswork on my part and may be completly wrong ( just going off what I have read here in the past and personal exp ) .

Ryan0260

4.56 would be a good gear with the 35's. Probably wont help with fuel economy guy it will put the engine back in its powerband and allow it to work more efficiently

raidue

I went 4.56s with my 35s and it's great on and off road. 5th and 6th gear can easily be used on the highway. And u can actually pass slow drivers now!

Fuel economy didn't change much to the good side but power is night and day difference. I was running 3.21s previously.

Surf City Dan

456 gears with 35's will keep you pretty close in RPMs to your stock set up.. With a 6sp it seems the majority of people run 488's with 35's. It gives optimal power and decent mileage. 513's is common in automatics since the 4sp auto is geared differently. If you increase tire size and keep your 321's it will not improve mileage due to your RPM being lower. Normally you find yourself deeper on the skinny pedal to maintain speed (even at a lower RPM) which reduces mileage. I run 456's and it seems strong with 315/70/R17's (34.5 inches). If I did it again I would probably throw in 488's.

Cosmo jk

I'm running 32's on 3.21's and I find that it is a pretty good combo sure I lost about 1 to 2 mpgs but definitely worth it. If you re gear to 4.56's you will get much worse mpgs then now but you will have a fast jeep lol and I find myself always in 6th gear my jeep doesn't feel like its killing itself to pull it either but it's all driving habits IMO and everyone drives different

BLACKJKUR

Just a thought, are you figuring your average MPG by filling up and dividing the mileage you've driven on that tank by the amount of gas you put in OR, are you going by your average mpg calculator that the Jeep has? Reason I ask this is, if you haven't reprogrammed for the larger tires, obviously your speedo is off BUT, so is your odometer and thus so is your Jeeps average mpg calculator. (not that it's the most accurate thing in the world anyway but...) When I reprogrammed for my 35's (up from stock Rubi 32's) my indicated average mpg went up. (still ain't great though, I average 13mpg, LOL!)

JCruz

What he said!




Since your speedo is off so is your odometer. You have no way of calculating actual miles traveled until you get it re calibrated.

Wgrin

I actually go by known miles, it's 200 miles door to door to my in-laws in Oklahoma. I fill up before I leave, before I come back, and when I get back.
I'm thinking 4.56 will be the answer for what I'm looking for.

atomthompson

I would regear. 14mpg with 3.21's is pretty ridiculous. I've got 3.73 with stock 32's and for highway I average around 24mpg because I can use the 6th gear to keep rpms down to about 2400, although I also have an air intake and exhaust. I'm thinking of going with 4.56 when I switch up. Especially if you plan on driving the highway. You might end up being stuck in 4th gear for all the hills if you don't. It's not just tire size, there's also the added torque required to turn the much heavier rubber. Here's a link with the rpm to gear ratio:

https://www.jk-forum.com/forums/show...276#post211276
Scroll down a little bit to find the charts.