I know, I know... This has been spoken about over and over again but I have had conflicting advise. I believed for a long time that 5.13 would be the way to go with am automatic but I have had some credit people with experience on jk and regearing say that 4.88 would be better suited for me. Please if anyone can give me a definitive answer that would be MUCH appreciated. Also would I better my MPG and with what one would I get better milage with. BTW, I have 35 inch Goodyear Duratracs and a Superchip.

 

Depends on your elevation, location(flat/mountains), how much time you spend driving highway/city.

You can look at your window sticker from when you bought the jeep or call your dealer with your VIN.

 

If I were you, I would go with the 5.13's. You will love the gears in the trails and it gives you an option to go with a bigger tire in the future without regearing. You won't notice a big difference on the road, the tranny makes up for it on the road.

 

I just put my 35's on Friday... I have the auto with 3.73 gears and I thought it would of been worse from what I have read. If I was to gear it I don't think the 5.13 would be my choice... I am close to sea level and not many hills.

 

I'm running 35's with an auto trans and 5.13's. It's real hilly around where I live so 4.88's didn't even cross my mind. I would have gone with 5.38's if I had a Rubi.
I think you would be happier with 5.13's if the terrain was hilly, if your terrain is flat like the Florida area then go with 4.88's.
70mph at 2300rpms I avg 17mpg

 

As with lifting advice, and tire advice, there simply is no 'definitive' answer. There is personal preference and driving style and location and setup and model and transmission and whatever else involved. One thing to pay attention to when reading a few thousand threads asking this same questiomn is:

-How many that went 4.88 wish they had 5.13
-How many that went 5.13 wish they had 5.38
-How many with an X/Sahara wish they had a front 44 so they could have gone 5.38
-And then compare the above with the number of people that went 5.13/5.38 and wish they had gone 4.88.
(hint - you will find a ton of people in the first 3 groups, and I think I have seen '3' people in the last group. And one of the three had a hemi, so he didn't even count)

So, why are your reputable contacts saying that 4.88's would be better suited?

Here is some more reading, with lots of comments and charts and stuff to make it easier to understand.
https://www.jk-forum.com/forums/show...gh-Altitude%29

 

I'm getting 5:38's on Tuesday, I have KM2 35's and SuperChip Flashpaq

Just sayin

 

I have 4.88s with 35s. I was told 5.13s will eat my gas mileage on the highways. I like the 4.88s too

 

I'll just tell you what I've experienced over the last few years. I've owned several Jeeps with this same auto transmission, and have used them with everything from 4.10 gears and 37" tires, to 4.88 gears with both 35" and 37" tires, to 5.38 gears with 35" tires. So I've pretty much tried them all.

I think 4.88 gears are the worst possible combination you can choose for highway use with this auto transmission. At one extreme, with the stock 4.10 gears, it will be more sluggish around town, but on the highway you just drive with the overdrive off, and third gear feels pretty decent. It is still geared so high that third gear is not over revving the engine, even driving down the interstate. At the other extreme, with 5.38 gears, it is geared low enough that it stays in overdrive for level ground, and even for some minor hills. But with 4.88 gears, you're right in the middle. It isn't geared low enough to stay in overdrive as well as it should, but when it downshifts to third gear it has to rev significantly higher than with stock gears. You don't feel like driving with overdrive off with 4.88 gears, and it won't stay in overdrive either. The Jeep I owned with 4.88 gears was the worst one I've owned for driving on the highway.

This is something you shouldn't do half-assed, and 4.88 gears are just that. Gear it low enough to make a difference. I recommend 5.13s.

 

You have to have a D44 up front, as 5.38's simply are not made for the d30. So if you have an x/sahara, you will either need to swap in a rubi44 or a PR44 or one of the D60's.