I’m running a 2018 JK 4 door with 4.5” lift, 35” tires. I actually just bought this Jeep. It’s not my first JK but my first really modified one. All the rest were stock lift, tires etc.
According to the build sheet it has 5:56 gears. Back when I was young I could go to the auto wreckers and swap out gear sets from other compatible diffs. Dana 30’s etc.
Can this still be done with these diffs, if the desired ratio is there? I actually don’t know exactly what diffs I have but they have had modifications for strength.
I have had about a 30 year break from serious wheeling and many things have changed so I thought I would ask.
This Jeep runs with high rpm on the road and sucks fuel like crazy. I ready a sticky that the ideal ratio should be 5:13.

 

That 5.56 is way big for 35s.. being as someone else did the build, per the build sheet are you sure that it has 5.56s.. AND NOT 4.56.. I checked Dana Spicer & no 5.56 is sold by that company. and I believe that the front is a Dana 30 and if still offered 5.38s were the lowest offered. Check for the gear ratio installed.. I would not consider running used gear sets; you still have to install a master kit. BTW I run 4.10s on 35s on our 2013 JKU and it is fine; we don't go for Rock Crawling.. Let the forum know what on your gears.

 

I actually do not know for sure what was written down for ratio is correct. I think my only option at the moment is to wait until spring when it’s warm enough outside to take the covers off and see what I’m dealing with. Whatever is in there doesn’t work well for commuting. I will be playing in the mud but not extreme rock crawling.

 

You might try this in the driveway: https://www.quadratec.com/content/ho...removing-cover

 

Agree, the lowest set for these axles are 5.38, and unlikely that you have those. Usually 4.56 is the sweet spot for the 3.6L and 35s, 4.88 to lean a little more aggressive if living around some big hills. The gear charts floating around on the web are fairly accurate if you know your true tire size (ground to center of hub x 2) and then note the rpms while cruising at 70mph. I wouldn't even consider a set of used gears in your '18. Regearing these days has gotten to a reasonable price in most areas. Heck, I think the going regear rate in my area for a JK is now about $1k-$1200 including parts. Up there in Calgary things might be pricier though.

 

I will definitely give this a try when the weather permits.

 

Thanks for all the input so far from everyone. I kind of feel dumb because I guess I really don't know what the actual ratio is at the moment. like I said earlier, it was on a piece of paper that I found it in the glove box after I got the jeep home. when this cold snap goes away i will be able to try and confirm for sure what ratio i have.

 

May not help at all as a previous owner may have regeared, but there are some sites that let you plug in your VIN # and get a build sheet. At least you can see what gears your jeep left the factory with.

https://fcacommunity.force.com/RAM/s/equipment-listing

 

The procedure in the link works fine, provided you can make sure both tires turn exactly together. Sometimes one tire will turn more than the other.
In that case, leave one tire on the ground and let the remaining tire turn 2 revolutions.