I've been going back and forth between getting a Wrangler sport and modifying it my self or getting a Rubicon X. A couple days ago I settled in the Rubi, but yesterday I found a 2013 sport S with just over 1000 miles (yes... 1k!) for $25k. It's got all the bells and whistles I would get on a new one, except the 3.73 axle. If I do go with the sport instead of the Rubi, I plan on putting a 2.5" lift and 35" tires on it. According to a chart I found on this forum, that is right at the limit of tire size for the 3.21 axle (1720 rpm @ 70 mph). Will I be happy with that? It will be 90% street, but not a daily driver. Any offroading that I do will be mud, dirt trails, and some sand (not much rock crawling here in central Illinois...). What are everyone's thoughts?
I have the 3.73 gears in my '12 JK sport. I have 33's (well, 305/70/16.. so sort of 33's) and a 2.5" RK lift. I would not be happy with 3.21 gears. I'm boarder line happy with the 3.73 and have 4.56 gears (and 35's) on my short list of next years mods. Mine is an auto, and not sure if you are looking at manual or auto. It's also my DD.
I have the 3.21 gears with Rubicon take offs. It works well that way. I can use Sixth gear on the my way to work at 50-55 here in PA. I am getting a built Dana 30 with gussets, CV axles, and C-bracing. Right now it has 5.13 in it, because the friend I am getting it from has 37" tires & an Automatic 3.8 Liter. I will regear it, and the 44 in the back with 4.56's when I move up to 35" tires. I will do it myself, because I can borrow the Dana tools I need.
The 3.21 gears are fine on our automatic 2013 Sahara - getting between 21 and 22mpg on the highway with cruise around 70mph. We do plan on lifting and putting on bigger tires though so see 4.56 gears in our future. To summarize - 3.21 is fine for stock tires but any increase in tire size will warrant deeper gears to keep you happy.
2013 JKU Sahara - ours
2001 TJ SE - hers, 2001 XJ Sport - ours
2003 TJ Sport - sold, 2000 TJ Sport - sold
1993 XJ Sport - totaled, 1987 XJ Laredo - sold
1987 XJ Chief - sold, 1953 CJ-3B - sold
I have a light 2013 2 door with 35's and 3.73. It sucks. I only use 6th gear on flat road and above 70. The engine just doesn't have the power at the lower rpm to pull larger tires. I run around 2000 rpm at 70 and it's no good. A rubi with 4.10's would be perfect though!
I guess if you have an auto it is less of an issue. It just won't use overdrive. When I get into hilly areas on the highway, I have to get my rowing skills on.
Final comment, 3.21 + standard transfer case + 35's = worthless off road for anything above mild. I'm swapping to a Rubi case next weekend. Although, I'd recommend that regardless of the gears.