AaronW

Age old question of what ratio should I pick??


I've got a beefed up Dana30 coming in for my JK, it'll be running 37s and is also a daily driver/highway driver.


I've got 4.56 ring a pinion sitting in the garage but have been told it might be a bit sluggish for 37s. It's a 3.6L auto and I'm currently running 35s and stock 3.73 ratios.


I don't want to lose my comfortable daily & highway driving by picking a ratio too high like 5.13/4.88, I also hear the teeth get too small at that ratio...


Thoughts?

ECHO

I think you will be fine with th4.56 .. 4.88 or 5.13 are a mileage killer on the highway... You have a 3.6 auto, I think you are right on track

Trail Jeeps

The age old question indeed, one of the most common questions we field.

It's true, the pinion teeth get freakishly small with a lot less contact than is ideal for a vehicle this size. That being said, some folks run them with little issue. For what it is, the Dana 30 is a remarkably strong axle design.

From a performance perspective, 5.13 is a good pick for 37s. If you wheel with a light foot, you will be ok. Keep wheel spin down, don't allow it to bounce.

Now, as far as a recommendation goes, if you wheel it hard I would just stick with a 4.88. There are always people out there who claim they have rock bouncers with a Dana 30 with 5.13s or 5.38s in their 900 horsepower home brew buggy and they like to drive one handed at night with the throttle pegged and no sh*ts given, but the reality is that a 5.13 gear is a liability with a Dana 30.

If you do choose to roll with a 5.13, make sure the installation and set up is done by a reputable installer, a good set up is key, and invest in good gears. Also invest is a good, beefy diff cover which does seem to keep things together a little better, the theory is that is doesn't allow as much deflection in the housing which would matter in this situation where every little bit of contact between the ring and pinion matters.

Happy Jeeping!

Trail Jeeps

To each his own, of course and everyone has their own experience, but in our experience 35s are sort of the threshold for attempting to balance fuel economy and fun factor. With 37s, we find that there isn't much to be done to maintain better fuel economy, the tires are just too big and heavy and that motor lacks to bottom end grunt to make up for the additional rolling resistance of 37s even with the NAG1, and any gains you make on the highway are erased by the engine laboring to get your heavy Jeep off the line and up freeway onramps. The one exception is if you do a lot of highway driving on flat, relatively wind free roads, then you might actually see practical gains to run higher gearing, but on hills and you'll find that the trans is constantly hunting for the right gear, even with a 4.56. A proper tune can help, but better mechanical advantage is the only way to help with that.

In the end you're probably better off looking to balance performance vs strength instead performance vs fuel economy, because if you're expecting fuel economy you'll probably just end up disappointed.

The most effective way to squeeze better fuel economy out of these pigs with big tires is to grab a set of less aggressive all terrain type tires and run them slightly overinflated, you'll actually get some pretty dramatic results vs running your standard issue knobbies at proper contact pressure.

ECHO

Makes perfect sense! great info - thanks

caryt

Don't waste any $ on a 30 if your running 37"unless its a Mall Queen.
At a min get a 44 and beef it up if your gona play on real rocks.

Ryan0260

I'm running 4.88's on my '15 which has a manual and 37's, and the ratio is perfect. It feels just like it did with the stock Rubicon tires and 4.10's.

tgoss

4.88's or 5.13's are the gear ratio you want for 3.6L auto... Personally run 5.13's now and it's perfect for around town and on the trail.

I'm going to have to ask why bother with a "beefed" up D30 as an axle upgrade for the front of your rig but to each his own. If that's what you stick with I would highly recommend NOT locking it either.

4wheels4life

I ran 5.13's in my 07 JK Dana 30, granted it was the 3.8 but it was fine for highway and offroad. I was just careful not to get the front end hopping when offraod and when I pulled them after the 6.0 LS swap they looked like new. Which by the way I have them for sale in the for sale section if you do choose to go with 5.13's

OnBelay

D30. ARB locker. 5.13s. EVO C-gussets and LCA skids. Dynatrac Prosteer ball joints. ARB diff cover. 35" Toyo R/Ts. It's a lot of money into a D30, but we never had $4K+ to spend on an axle at one time. I think others are in the same position. It's gotten us by OK, but we don't wheel extremely hard right now. And when we do wheel, we don't lock the front, smash the throttle, and turn the front wheels.

A 60/80 combo + LS is in the works for 4-5 years from now though haha!