Northridge4x4

I am considering 4.10's as stock. For my purposes of this poll I only need to know about 4.56 and higher

panthermark

4.88's on a +2012 auto sounds like it is either a near dedicated off-road rig, or you live on the side of a mountain, or the shop that did the swap was stuck in 2007-2011.

JKBANDIT55

Currently running 3.73 with 37s auto. Honestly its not bad. Only thing is, I live in Denver Colorado, this whole state is full of hills. And in the mountains my RPMs run semi high.

With my 35s, this was a perfect set up.

I plan on going 4.88 soon, and those should do well on 40s when I reach that level.

itsthelaw

Currently running 4.88 on 2013 2dr with auto and 35" Nittos on alloys. I have wheeled it, run it down the highway for hours, and drive it daily in town. I cannot find a thing wrong with 4.88 other than my MPG is 14.5 in town, but getting about 16.5 on highway at 70-75 mph and higher. I don't care about the MPG, so I am pro 4.88.

I started with stock 16" wheels and 3.21. When I put on the 35" tires, I drove it for a few weeks and it was not fun. I even drove 5 hours on the highway, which was hell. I think the 4.88 gearing with the 35" tires is very close to the stock setup that I started with on the Jeep.

Lusky

2013 Auto 2 door:
I ran 3.73 on 37" BFG AT KO's then switched to 4.56 and it was great. Then I switched to 37" MT/R Kevlars and its still great. I think 4.10
Is correct for 35's that dont truly measure 35".

Here is pics of 37 BFG next to 37 MT/R

planman

Don't fear the gear. This is a fairly old saying, but is the same today as it was decades ago.

If 4.10s were ideal for 35s, they wouldn't work well with stock 32s.

A gas 3.6L engine is designed to be more efficient with higher rpms. It isn't a diesel engine.

The transmission gear ratio on 12+ automatics has a 5th gear ratio of 0.83:1. That is fairly close to the 6th gear transmission gear ratio for a 6 speed. The appropriate gear ratios would be somewhat similar to 6 speed JKs--even 07-11s.

Optimal performance for mixed driving a 12+ with 35s will be 4.56 or 4.88, depending on the weight of your rig and the elevation and hills/mountains where you live. 5.13s would work well for a rig that isn't driven much over 70 mph.

Optimal performance with 32s will be 3.73s or 4.10s, depending on weight load and where you live. This is why these ratios are on stock Rubicons.

It would be a waste of money for a non-Rubi owner to regear to 4.10s to run larger than 32s.

You could drive a 3.6L cross country at 4500 rpm and it wouldn't hurt anything but fuel economy. The engine certainly won't blow up at 3000 rpm for long trips either.

Someone should do 0-60 time tests, 75 mph extended freeway mpg tests, and in town mpg test with 35s and 4.10s, and then upgrade to 4.56s or 4.88s with the same tests and put opinions to rest with actual performance and mpg facts.

jetmechabq

I have bfg km2 that are 35x12.50x17

rays0852

I respect everything you have put out on this forum but I could not disagree more with your opinion on this.

Spinning an engine at over 3000 RPMs for an extended road trip year after year will wear both the engine and trans prematurely.

Also 4.56 would be a great gear for 35s but many of us run 4.10s and think its great. I re geared to 4.10s and love it. Where I live every worthwhile trail is 2-3 hrs away. 4.88 + is just too much.

planman

Yes. We would somewhat disagree about the rpms. The Pentastar rates at max HP at 6,400 rpm, and it redlines above that. This is no diesel or old school engine that redlines at a much lower rpm.

A stock 12+ Rubicon automatic with 4.10 gears and 32" tires runs over 2,500 rpm at 70 mph, and over 3,000 rpm at 85 mph. That jeep comes with a factory 5 year/100,000 mile drivetrain warranty. This means that if you drive it 99.999 miles back and forth across the country at 85 mph, over 3,000 rpm, and the engine fails, Chrysler will pay parts and labor to install a new engine. I am confident that the Jeep engineers and the bean counters would not give a 100,000 mile drivetrain warranty on an engine that could not handle 3,000 rpm.

I come from the world of motorcycles, where many of those engines redline at over 12,000 rpm and run efficiently at higher relatively high rpms.

4.88s would turn most full size 35s at about 2700 rpm at 70 mph. This is only 200 rpm more than at stock Rubi automatic, with stock tires and wheels. I don't believe an extra 200 rpm at 70 mph or an extra 350 rpm at 85 mph will cause a Pentastar to fail prematurely. If I had a heavy 4dr rig and lived in the Rocky Mountains, I'd want the extra horsepower from the extra 200-350 rpm to drive those mountain passes.

Of course, if I lived at sea level and had a lighter rig, I would not benefit as much from the extra 200-350 rpm, and I would run taller gears--somewhat agreeing with your experience. However, I'd still run 4.56 gears at sea level in Florida because the extra highway rpm isn't that much over 4.10s, but the in-town fuel economy and off road performance of 4.56s would be superior to 4.10s.

Now, would I want to run it 100,000 miles at 4,500 rpm? No. But my concern with the Pentastar would be more about fuel economy than about engine longevity. It is a very good engine.

Brightwhite

I have 4:88's in my 2012 JKU with 35's - live in Colorado. The 4:88's are a little steep for day-to-day driving in Denver. Anything putzing around 35-55 is fine, but flat, running 75mph down the interstate runs a little high on the rpm's. However, loaded down and going up a mountain pass and anything off road it's great.