I have a 2010 Sport and I am running a 3.5" lift with 35" bfg km2s. Of course I have the 3.8 with the 3.73 gears now. I am looking at changing out to a 4.88 or a 5.13. What do you guys think? Would I be happy with those or do I need to go with something different?

 

On my '09 automatic 3.8 I initially did 4.88's and was disappointed later that I hadn't gone deeper. I started with 35s, went to 37s later with about the same performance. After taking out a rear pinion bearing in Moab I popped for Northridges Yukon deal on a set of 5.38s. Have never looked back.

 

5.13 for D30 is the deepest you can go 5.38 for a D44. I also went 5.38 for 37s. PERFECT!

 

What RPM are you guys running on the highway? That's one thing that concerns me since it is my daily driver.

 

Here is a great side by side calculator, which allows you to see the impact of gear and or tire changes...

Shows you RPM at different speed as well as crawl ratios. Etc.

http://www.grimmjeeper.com/gears.html

 

These charts were designed by a member of this forum, no idea why they are no longer hosted here. They are not generic one size fits all, or fill in the blanks, but designed specifically for the JK, and broken down by engine and transmission.



Measure your tires and plug it in. (measured, not mfg spec!!)

The OD ratio is .69, so to get OD Off, just divide the OD/On by that number.

ex. (3.8 auto, 35's that measure 34")
3.73 = 1781 rpm @ 70
5.13 = 2450 rpm @ 70

If you turn the OD Off, divide by .69

1781 / .69 = 2581 rpm @ 70 (about 130 rpm more than you would have with 5.13's. Close enough for you to jump on the freeway and get an idea of where you will end up.)

 

I'm running 35's with 4.88 but I'm 6speed 3.8 I feel like is just perfect not sure if you have auto?

 

5.38 with 37s auto 3.8, 2100rpm at 60 mph

 

Awesome! All of your info was very helpful. The charts were a huge help. Thank you guys. I will update you on what I decide in the weeks to come!