Just curious...

I am researching my next mod, the gears. Originally, i was leaning toward 4.56, but the more i read the more everyone says go to 4.88. I have 2012 JKU 35s with 3.21 auto. The 3.21 actually wasnt as bad as i expected after lift and tire upgrade. Acceleration and highway cruising at 75 wasnt all that noticeable, but i do want to add more weight with bumpers and towing.

So, that said..pricing 4.56 vs 4.88, the 4.88 is way less expensive. Any reason why? I would think 4.88 would be more $$$

 

Check out 4ws.com for gears. They have the best prices I've seen. 4.56's are much less common in the reverse pattern that our jk's have.

 

I have 4.88's and I love them! You will not be unhappy. Do it!

 

4.88 is too much for 35's. I ran 4.56 on two different sets if 37's. The first set measured out 35.25 and the current 37's measure 36.9 and it is plenty of gear on my 13 2 door. I have heavy bumpers, winch, 37" spare, tools, added insulation.

 

I'm doing 4.88 on my 2010 JKUS with auto. Already got the gears and am doing it myself because I don't trust anyone close to do it right.

I've been told by several here that I should be going to 5.13 but that's not me. Two main reasons (which may be flawed but that's OK) are:
1) Lower driveshaft RPMs at highway speed so driveshaft should last longer, less vibration.
2) I believe 4.88 gears are stronger and will last longer than 5.13 in a D30.

I often drive interstate speeds.

 

I have 4.56 on my 2012 jku with 35" nitro trail grapplers. No issue at all, and love the way it drives.

 

It's very important to remember what that if you have have the new motor and trans you want one number lower than us with the 07-11. For example, if you have the older 3.8 motor and auto trans with 35's, 4.88's are a great overall choice. If you have the new 3.6 with auto and 35's, 4.56 is the preferred choice. The type of wheeling and your physical location (mountains, beach, etc) will need to be factored in.

 

As has been said, 4.56s are less in demand, so fewer are made. So, the cost to make them is more per unit.

4.88s with 35" tires that measure 34" mounted on a 12+ automatic till turn about 200 more rpm at 75 mph than 4.56s.

If you are going to tow or be heavy, you will want the extra power generated by the extra 200 rpm.

An extra 200 rpm at 75 mph will make almost no meaningful difference in fuel economy and absolutely no difference in engine or drivetrain longevity.

Your heavy weight, aggressive tires, leveled suspension, etc., will make much more difference in lower mpg than an extra 200 rpm.

All this is why people are generally advised by those with experience to do 4.88s instead of 4.56s in your circumstance.

 

At 75 mph, 5.13s will turn about 125 more engine rpm for you than 4.88s.

At 75 mph, your driveshaft will turn 185 rpm faster with 5.13s than with 4.88s. If your driveshaft is unbalanced at 3802 rpm, it will cause the same problems at 3617 rpm.

The JK is now 6 years old. There is no evidence that people have broken 5.13s in a Dana 30 anymore than with 4.88s. There are plenty of threads about how weak the stock ball joints are, but there almost no threads about multiple people breaking 5.13s in Dana 30s that wouldn't have broken 4.88s.

So, you are saying that 125 engine rpm, 185 driveshaft rpm, and a supposition without any evidence over the last 6 years of 5.13s being the weak link in a Dana 30 are the basis for going with 4.88s in an 07-11 automatic on 35s. Correct?

 

I did 4.88's to turn my 35's and it seems to be a nice choice for me, I have no complaints or regrets about it...two thumbs up.