I assume you know that you need the same gears in both axles. I have a 2013 daily driver and upgraded the gears to 4.88 to run BFG 35s (really 34s). Around town the MPG didn't really change. On the interstate it would get around 14mpg at 75mph-ish. If it ran slower at 65mph the mpg would go up to almost 16. Worked well both on and off road. Now with the 37" Nittos installed, I wish I went with 5.13s.

 

I personally feel that 4.88’s are too short for 35’s on the highway, but I seem to be in the minority on this forum. Anytime you get better MPG’s driving in town than you do on the highway, something ain’t right.


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I run 4.88s with 35x10.50 Kenda klevers. The gears are short but not too short for me. I have a stick and the highway seems fine to me. I never have to downshift on hills or to pass. There is always power. I can also pull out in 2nd sometimes.

Wheeling is great too with the lower gears. I work from home and my Jeep is my toy, but I drive it most of the time anyway. I do not think 4.10 gears are good with 35s. I know this because I had them in my Rubicon before I swapped in the 4.88s. Tolerable is the best description. Go for 4.88 gears and do not look back. If you go up to 37s at some point the gears will be tolerable but will work, not so with 4.10s.

 

Since you are in a two door and that is lighter than a four door, 4.88's should be ok for 37's provided you aren't at high altitude and keep your Jeep light. I have 5.13's in my four door that weighs about 6100 pounds when I last weighed it before putting on the 37's and am glad I went 5.13. Just my opinion. Good luck with your build.

 

My 2010 2 door manual had 4.88s on 35s and was absolutely perfect. Yes, my milage was better around town, but it towed my small boat flawlessly on the highway too.
I would have gone to at least 5.13s if running 37s however.
Troy

 

Im installing 5.13's this week w 35 inch tires. 2011 JK Unlimited Rubi Auto. Looking forward to having the correct gear ratio.

 

The 3.8 and 3.6 are apples and oranges. I don’t know what the OP has.

Generally speaking it’s hard to overgear the 3.8 if you have oversized tires, particularly if you have an AT. I would not go less than 5.13s with 35s, 4.88s with 34s, 4.56 with 33s, etc.

 

I’ve got the

The 3.8 and 3.6 are apples and oranges. I don’t know what the OP has.

Generally speaking it’s hard to overgear the 3.8 if you have oversized tires, particularly if you have an AT. I would not go less than 5.13s with 35s, 4.88s with 34s, 4.56 with 33s, etc.

I’ve got the 3.6. I feel like 4.56 should be a good choice for running both 35s and 37s not looking to make my Jeep sporty just get it in an ideal RPM range for the highway

 

Just buy the gearing that you want and adapt your driving style to maximize your mileage. I still think 4.88 is the better choice if 37s are in your future particularly since you don't have a Rubicon transfer case and you talk about offloading a lot. If mileage is important to you, realistically you should stick with 35s and 4.56 gears. On a 2-door this will still allow you to do almost all the trails you will ever want to do with good skills and spotter.

 

New here
I was wondering the same thing. I have a 13 jku rubicon and live in the Boston mountains area of northwest Arkansas. Jeep has bumpers, winch, all the extra skids, sliders, high lift jack, light bar. I had 35’s and took them off pretty quick because of all the downshifting to 3rd even out on the interstate.
I am leaning towards 4:88 with 35’s because all the downshifting drives me crazy. I drive rural highways and roads mostly but love aggressive trails and twice a month I have to run 70mph a couple hours on interstate. Would 4:88 be a good fit?
Any help would be greatly appreciated

 

4.88's would be perfect for your Rubi. I regeared my 13 JKUR with 35s a few years ago and went with 4.88's. I drive on the highways daily and hit 70+ mph every day, along with a 2600' ft elevation drop and climb dropping off and picking up the kids. If I was just driving around town and not on the highways, I may have gone 5.13s, but 4.88s are ideal for 35s with any kind of hills or mountains and then highway. My JKU came with 4.10's from the factory, so 4.56 wouldn't make much sense. Good luck, regearing is one of those thing you'll wish you had done sooner.

And welcome to WF!

 

Welcome from Arizona.

 

Thank you for the replies
I don’t believe I will be going with 37’s
I go places with my 33’s that are on it now that others think they need 37’s. I drag the belly and bump the diffs sometimes but I think 35’s will be perfect for my use.

 

4.88 and 35's are fine. At 70 mph you are probably turning 2800 rpms. with a auto and about 150 less with a manual. I have run all day at 80 mph in the summer time and the vehicle has never complained. Now that I am on 37 I am down to 2500 rpms and I am up about 1 mpg but it struggles much harder in the mountains.

FYI: The highest mpg I ever got is with 4.88's and 35's, just shy of 21 mpg. Speed limit 55mph little to no wind and it was there it was a tail wind. And it was much easy to wheel being a manual.

 

That’s awesome! I seen 21.8 mpg the other day after a 3 hour highway drive of mixed mountain and flat free way driving this being with 3.73s and 33inch ko2s

 

I always answer this question the same way (as a general rule of thumb). How fast do you feel compelled to drive on the freeway?

If you are like one of those people I see driving 80 mph in the fast lane with 37's and don't mind giving up a LOT of control while off-road (and never tow anything) then use a numerically lower gear, especially if you have an automatic trans. For me, I like to drive 65-70 (and usually 65 when I tow my camping trailer). With a manual trans (0.8 overdrive gear ratio) I am very happy with 4.88 gears and 34" tires (BFG 315's). Here's a small screen shot of a calculator I built when I was trying to decide on tire sizes and gear ratios. I've arbitrarily set the color code as follows:

white = not recommended
Yellow = "I like to drive fast on the freeway and don't care as much about rock crawling or towing"
Green = Optimal balance for a lot of people
Blue = Better towing & rock crawling and willing to sacrifice "go fast" on the highway. Better drivability around town.

(note this is assuming a 1.00 top gear. If you have an automatic, you'd divide by 0.83 for overdrive and if you have a manual you'd divide by 0.8)

 

The moral of the story here is there is ZERO guarantee what anyone will get MPG wise with "XX" gears and "XX" tire size. Selecting any gear ratio with the idea that you'll get better MPG with one vs. the other is pointless. A crap shoot. I've been on hundreds of these threads by now. There are simply too many factors that affect mileage. One person gets 20, the next person chimes in at 15 MPG. 2 door, 4 door, terrain, weight of your right foot. For a moment think logically and not like a Jeep owner. WHY WOULD YOU SPEND $$$$ on tires, wheels and a re-gear to be concerned if you'll get 15 or 17 MPH? If your gas budget every month is that tight then why get 35s to being with? Neither 4.56s or 4.88s will be drastically different from one another. Pick one. You will NOT be disappointed in either because once you drive the Jeep without the god-awhile 3.21 or 3.45s or whatever you have....you'll be giddy over the difference.

 

EXACTLY!

 

 

4:88’s and 35’s are perfect for me. 3.6 auto. I turn around 3000 rpm at 70 ish mph. I am getting around 15 mpg on average. I drive 18 mi each way to work over a 1,000 ft pass. 28 to 30 psi.

I have never actually calculated my mileage. I just look at the computer from time to time. When I made the decision to go to bigger tires , I became willing to accept the negative consequences. I also commute on my motorcycle most of the time anyway.

 

Forgot to update you guys but I went to 4.88s a while ago. I’m driving around on 33s right now actually. It feels fine for now, waiting on some 35s to come back in stock

 

How much did the labor cost for the upgrade? I know I can get the gears for less than a grand but I am not sure what a good price on labor would be. Or did you do it yourself?

 

My 4.88 arrived today. Running 3.21 with 35x12.5x 18 now.

 

When I regeared my 2013 JKR automatic, I went with 4:56 for 35 inch tires. Worked very well. Currently running 37 inch tires. Still works well. Never had any issues in Moab or Colorado! I do not tow anything and do not worry about gas milage! As soon as I find a decent tire, I will be going back to 35 inch tires. No need for any brake modifications other than EBC greenstuff brake pads!

 

I'm probably in the minority here, but I'm happy with my 3.73, gearing with 37's, and the 4:1. On my 2010.

I get around 18 on average as long as I keep it under 70mph.

That is as measured by actual distance traveled, not as indicated. The odometer is off by about 450 feet per mile. And the cluster says 13.8-12.1L/.
But it's confirmed by actual consumption and actual distance.

I think some people forget to compensate for the difference in tire size, for instance going from 33.5inch tires to 37 is about a 10% difference, so if the cluster says 17MPG it's actually 18.7MPG
Or for instance 13.5L/ it's actually 12.15L/ ish.

 

I'm probably in the minority here, but I'm happy with my 3.73, gearing with 37's, and the 4:1. On my 2010.

I get around 18 on average as long as I keep it under 70mph.

That is as measured by actual distance traveled, not as indicated. The odometer is off by about 450 feet per mile. And the cluster says 13.8-12.1L/.
But it's confirmed by actual consumption and actual distance.

I think some people forget to compensate for the difference in tire size, for instance going from 33.5inch tires to 37 is about a 10% difference, so if the cluster says 17MPG it's actually 18.7MPG
Or for instance 13.5L/ it's actually 12.15L/ ish.

If you use an OBDII adapter and Jscan or the Flashcal, you can update the computer with your new ACTUAL tire size and the computer will not only adjust the speedometer, but it will also automatically adjust for the mileage as well. Each time I have put new tires on mine I had to adjust for the true measured size so I could have accurate speedometer readings so I don't get a speeding ticket. You also need to adjust for new gears when changing those as well.

 

All I know is that I am running 3.73 in my 2016 Rubicon, (Special Ordered by the original owner for some reason) on 35's and while I am in general happy with the performance, maintaining 80 mph when that's the speedlimit whrere I live is near impossible. Not without feeling like the engine is going to explode anyway. I also want to be able to reliably tow a camping trailer with this thing and I fear that I will upgrade to the wrong gears as I am thinking 4.11 but also considering upgrading to 37's in the future.

 

don't mean to thread jack, but after reading all 4 pages, I want to ask my question in this thread so as to not create yet another thread about gearing because there are so many....

2014 JKUR 6 Speed Manual currently on 35x12.5r17 and 4:10 stock gears
3.5 Metalcloak lift
looking to go to 37x12.50r17
Mammoth Wheels D window 17x9

I was considering 4:88 based off the review from Jason Auto Edits channel on youtube. He has a 2013 I believe like mine, 6spd manual, and went 4:88. I'm not sure what he's on now since he's no longer on the stock axles. What are you thoughts? 4:88 or 5:13?

Again, I plan to upgrade to 37s, I don't tow in my jeep at all. I live in southern CA, and most the trails I do are overland/mild in nature, I don't rock crawl at all. I get flexy on some technical trails, but I don't rock crawl or slam the jeep on rocks. My driving is mostly street city, and a mixture of highway, but definitely more street than highway due to how close my job is to my home. I have steel bumpers, winch, no rack or other heavy stuff that I carry.

I don't have any supporting mods for 37s yet either. Was considering C gussets, new ball joints from Dynatrac, and really that's it for now. Upgrade my brake pads perhaps to the greenstuff ones.


Your professional input from YOUR ACTUAL EXPERIENCES is greatly appreciated.

 

I have a 2013 JK 10A w/6spd Manual, 35x10.50R17 tires and 4.88 gears. I'm not super heavy, steel bumpers, winch, aluminum flat skids and some tools, not much else. I think it is perfect for all scenarios. It is terrific on the highway, but I don't really get to altitude so I cannot fully speak to mountain performance. It crawls terrific and I only use 1st for the most technical of rock crawling. I can pull out in 2nd sometimes too.

I think with 37s and a 4 door you will be happiest w/5:13, Not to mention California does have actual mountains. I don't think you will regret it, and I have no recollection of anyone saying I wish I did not gear this so low.

 

@aaaslayer been there, done that, only mine is a 2 door and probably heavier than your rig. When I was still on 35's I regeared to 4.88 and it was perfect, I had no plan to go to 37's. Years later I having gone to 37's. 37's are workable with 4.88 gears, better than 35's and 4.10 but not has good as 5.13's would be.

I do get slightly better mpg with the 37's but I am also shifting more often. I used to be able to run up Cajon pass, I live in Hesperia, in 6th gear on 35's on all but the hottest days. With 37's I'm in 5th almost the entire way from the 15/215 merge to the top.

If I had any idea that I would be on 37's all those years ago I would of gone 5.13's. I regeared only for on road performance. And there have been a couple of times even with 4.88 and 35's where 5.13's would of been the better choice like spending a week above 6000 feet. If I ever upgrade my axles to d60's 5.13's will be my gear of choice.


We could always arrange a demonstration, we don't live that far apart.

 

@aaaslayer been there, done that, only mine is a 2 door and probably heavier than your rig. When I was still on 35's I regeared to 4.88 and it was perfect, I had no plan to go to 37's. Years later I having gone to 37's. 37's are workable with 4.88 gears, better than 35's and 4.10 but not has good as 5.13's would be.

I do get slightly better mpg with the 37's but I am also shifting more often. I used to be able to run up Cajon pass, I live in Hesperia, in 6th gear on 35's on all but the hottest days. With 37's I'm in 5th almost the entire way from the 15/215 merge to the top.

If I had any idea that I would be on 37's all those years ago I would of gone 5.13's. I regeared only for on road performance. And there have been a couple of times even with 4.88 and 35's where 5.13's would of been the better choice like spending a week above 6000 feet. If I ever upgrade my axles to d60's 5.13's will be my gear of choice.


We could always arrange a demonstration, we don't live that far apart.

Were you able to tow with 4.88's on 35's adequately and with no issues?