I'm in the same boat man. Except I have 3.21 gears with 33's and I feel like when the transmission shifts into the next higher gear it really bogs the motor down. The 3.6 doesn't seem to have much power before 2k rpms. It bogs to the point where my heat shields create an annoying vibration. I took the jeep to the dealer and they tightened the heat shields down, but it still makes the noise.

Thinking the 4.10's should be sufficient as an upgrade, but I know after these tires wear out I might consider 35's and will want more gear. I can't really do 80 mph where I'm located without getting a ticket, so cruising at 80mph is not much of a concern. According to the 3.6L graph, 33" tires with 4.56 gears puts me at 2,698 rpms @ 70 MPH. Is this too much for the stock drive shaft? Gas mileage isnt much of a concern either, as I am only getting about 16.5 mpg average according to the dash.

 

If you look online there are some gear ratio tire size calculators that may help you. when I went to 4.88's and 37's I used one to find out what my ratio would be with larger tires so I could get as close to 4.10 final as possible. I run 75 - 80 mph with 37's everyday on 4.88 gears and no problems but using the calculators I was able to hit close to 4.10 final ratio as possible. This with the charts are pretty accurate for figuring where RPMs will be.

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I'm in a 2012 JKU Sport. When I upgraded to 2.5" lift and 35" tires (actual 34.5), my 3.73 gear ratio was adequate in town, sucked on the highway, and forget about hills. I went to 4.56 gears and it's been perfect for me. I drove from Texas to Colorado and did the silver mine trails, and it always felt good whether on- or off-road.

I do 80-90 all the time, and when I do, my gas mileage sucks. I probably lost 5 mpg going from stock to where I am now. I agree that much of the MPG loss occurs at 65 MPH and up, but- there's also a lot of gas burned getting off the line. I can save an MPG or two just by laying off the skinny pedal. Well some days I can.

 

Your drive shaft u-joint life is also decreased, the higher your average Rpm is.

 

I recently lifted 2014 JKUR with 6sp and am running 315/70/17 duratracs. At first I was planning to re-gear from 4.10 to 4.56 to get it back to stock like rubi gearing. After driving and doing research, from what I can determine the set up I now have is pretty much like running 3.73s on stock 255/75/17.. This is what a lot of jeeps come with from factory. Not a race car, but gets up and goes pretty good.

I have decided to hold off on doing to deeper gear for now, Given that I have the 4:1 transfer-case, lockers, and I am not a rock crawler.. I should be more that okay off road with this setup . Figure I have better engine life, better mileage, and better/easier cruising speed along with good off road capability, better that anything stock except a rubi (from a gearing perspective).

Am I missing anything in my thought process?

 

Just curious as to the highway mileage you do get at those speeds?


What are the stock driveshafts rated for. Based on some calculations, the driveshaft of a stock rubicon at 80 mph is spinning 3556 rpm and stock sport with 29" tires and 3.73 gears will have a drive shaft rpm of 3500 at 80 mph.

 

Now I am moving soon wich will be about 10 miles from work but for the last year I have been doing 100 miles round trip to and from work. I run my Rubicon between 80 and 85 MPH. I have not had any issues. My 3.6 sees 3k A LOT is that bad?

 

I honestly do not think so, the redline is 6400 RPM and there is no increased engine noise from 2500 to 3200 that I can tell.

Any Chrysler engineers in the know out there?

 

We have over 42,000 miles since new on a stock '13 JKUR with 4.10's and the 6-speed. It goes down the freeway all day long between 70-80mph and no issues to report. We keep a close eye on things like u-joints, and they seem to be wearing appropriately.

I'm in a similar boat as the OP.... 33's and 3.73's in my 2-door sport, also a 3.6. Thinking about a regear eventually.

The Jeep falls flat on its face on mountain grades, and I'm often grabbing 5th or 4th to maintain adequate speed.

What I'm curious about....lots of people saying they drive 70, 80++ mph in their lifted Jeeps, and towing is part of the conversation too. I don't know that I'd personally tow anything that fast, with any rig. Certainly not my 2-door. Not judging, but in my experienc-- I don't even like to drive it that fast and I supposedly have done all the correct things for my 2.5" lift. The Jeep just handles poorly as a rule of thumb, and it gets blown around if there's any wind, and the larger tires (even though balanced, wheels are round) still creates a lot of vibration at higher speeds. Just doesn't feel great after 70mph. Maybe I'm missing something?

I'd probably be looking at 4.56 or 4.88's for my gear upgrade, but like others, need to decide if I'm sticking with 33's first. I think I am..it's been a really great setup for me on and off road.

 

I have a JKU and I do not tow at 80MPH, Most trailer tires are not rated to go above 65mph. I usually just tow my skis around town to and from the ramp, and my utility trailer I drive on the highway to get to the local Lowes. Its actually not to bad since I never load it down. I really notice trying to start with my skis which is right around the 3500lb mark.

As far a driving on the freeway with a lifted Jeep and bigger tires, I experience no vibrations and I have taken it up to 90mph. I have had to get my tires balanced after my first rotation and since then they have been great. Road force balancing made a huge difference. I might be crazy I don't know, but I do 80 every day on my way to work and its fine, sure the wind will push you around a little, but not enough to cause steering issues.