I have 5:38's and its not to much, I wish I would of saved my money and went with Dana 60's. A little more money, but now I want the V8 too.

 

That gear chart isn't real life. Real life for me was on a return from wheeling in Disney, the group of us had to hold our speed on the turnpike to 70-MPH because one Jeep had 35s, six speed and 5.13s. He said he could not hold 75-MPH (the speed limit). The rule of thumb is 4.88s for a six speed with 35s and 5.13s for an auto. It's a good rule of thumb.

As for people who say that they live in a flat area--Do you plan to never leave the area where you live? Even here in Oklahoma, which is generally considered pretty flat, we have enough up and down hills to make down-shifts necessary when not properly geared. Think about it: Do you want to have shifting problems when you head out on vacation?

 

From a power perspective it doesn't make any sense as to why they couldn't maintain 75mph. From the perspective of their comfort level twisting the engine at over 3,000 rpm they probably didn't have the stomach for it. It's not a lot of power per stroke and likewise I too like to stay under 3,000 rpm just from feel. I don't think it would dissuade me from keeping up with the pack, but by design that's where I would draw the line.

As for the OP, what planman stated is the same as what I would have mentioned with a little different verbiage.

 

That gear chart is mathematically perfect. If your vehicle doesn't follow it then your tires are not exactly the size you are going off. I have ran three different gears each with five different tires, and the chart was exactly perfect.

 

I have a 6 speed with 37's and have 5.13. They work great! Great improvement over the stok gearing. I dont think I would go much lower though. 70% of my driving is in town.

 

I like my 5:13 w/35" tires they are just right for me still 14/15 MPG and its better than stock.

 

What about in the long run? Will running my X, on 35s, at over 3000 rpms over time stress the 3.8? I'm thinking further down the road you would be doing work to the engine. I'm also a gear noob and have been considering regearing. I live in maine and I am not happy with constantly downshifting on a paved road. Thanks for the info guys!

 

im in the same boat as this thread author and my neighbor is telling me to go 4.88s. reading this is making me want 5.13s but i off road probably once or twice a month and it isnt that hard. should i still go with 5.13s or 4.88s? i drive 40 miles a day and dont want to make a bad choice. i do care about gas mileage and rpms, but am very much a gear noob!

edit: auto unlimited X with 315/75/16 goodyear wrangler duratracs not going to 37s

 

My Jeep is a auto and 4dr x with 35x12.50x18 and I'm running 5:13 couldn't have picked a better gear for me. I off road a little and hunt a lot I can run down the interstate at 70 MPH and it turns 2400 rpm. I started to go with 4:88 but glad I didn't I wouldn't have been happy even my wife said the Jeep runs better than it did with smaller tires and stock 3:73

 

You have all the info you need right here in this one thread. If the number of people saying 5.13 is the ratio to go with for an auto on 35's isn't good enough for you, then go back to post 12 and look at the numbers. The only ratio that would be better is 5.38's. (But you would need a front 44 to run them, so...)


Why is your neighbor saying 4.88? Does he have a JK? Is it an auto? Does it have 35's? Most of the people that suggest under-gearing auto's either don't OWN a JK, or are basing their opinion off of a manual transmission. You can't base an opinion on some other vehicle with a completely different engine/transmission/R&P setup. You can't even base the choice of auto JK gears using your experience with a manual JK...