JK: axle ratio choice

[buellman]

Hey guys, just got a new jeep recently 3.6L auto and 4.10s. Started to upgrade it and have 35s on it wondering what axle ratio i should change to. I use it as a daily driver and love to wheel and also im looking at getting some decent gas mileage. Anyone got something similar. Thanks.

[vwtipeii]

4.56 should work just fine with an auto.

http://www.google.com/imgres?imgurl=...QEwBA&dur=1504

[Ol Man]

I put 5.13s in my 2008 Rubicon JK with 35s. I would guess the combination of tires and gearing cut my mileage by about 10%.

[mkjeepers]

I would suggest talking to a few 4x shops that are up on the new model JK's (2012 & up) for advice. The gearing is vastly different between the 2007 - 2011 models and the new 3.6.
My 2012 2 door with auto trans has 3.21's and feels lower gerared than
my 2007 was with 4.11's with the same tire size - power wise, RPM and speed range is very different in the two vehicles.

[vwtipeii]

agreed. you basically want to find a gearset that keeps your stock rpm range, shift points and power band

[dirtman13]

4.56 should work just fine with an auto.

http://www.google.com/imgres?imgurl=...QEwBA&dur=1504

It's a little more complex then just that diagram.
This is a good tool RPM Calculator to figure out what might work but Mike brings up a good point. Probably best to check with someone that has experience with the new vehicles.

[flatout]

Try this

[Toolman]

I looked into it a while ago and as I understand it, if you change the gear set in the 2012's the ECU needs to be reprogrammed at the stealership, otherwise it goes into "limp mode".
AEV makes some cool gadgetry to help with this issue also.

[mrchips]

Mike, Ronnie first put 4.56 in a 07 JK with auto tranny, they failed but then he upgraded to 4.88, and likes it much better. That mini van motor is gutless, I would also go 4.88 with 35's

[mrchips]

Got it, Pentastar motor, still would go 4.88

[Toolman]

Yep, 488's are my choice as well however my van has 410's with a NP271 transfer case. With this combo it put the shift points within the factory parameters so I was able to get the speedo spot on. It is fine on the highway and towing the jeep but, in the dirt on a descent in 4LO the gearing should be lower (2.7:1) in my opinion. 4 speed Atlas coming soon.
Which leads me to believe that with the 4:1 transfer case in the RUBI the 410's would be fine for a while with 35's. However in the future if I decide to build that pile I will pull the axles before I waste the coin on gearing it. All my research as lead me to one conclusion on that project.
Leave it alone and beat up the TJ and use the Van for expo trips. Let her enjoy it the way it is because she loves it and that's all that really matters.

On another note. After 8700 miles it needed the cylinder head replaced the ecm code showed #6 cylinder misfire. Checked the TSB's and sure enough. Factory "campaign" one of those "only replace head if it happens" recall. At that point I lost all confidence in that motor,
To be honest I'm not sure if we're even keeping it.

[Tumbleweed13]

Mike, I think the " mini van motor" Chips was referring to, is the JK's 3.8L, Not Vandetta"s.

[TipsE-Z]

I'm running the minivan motor with 5:13s. I don't think I'd go any higher than those, if you ever even think you may put 37s on there I'd go to 5:38s. Gas mileage will suck, but if that was a concern buy a Prius. I get about 17 on the highway, 13 around town. The Jeep pulled a 10 foot trailer with my bike on it with no real issue, but struggled a bit with a 14 foot trailer and my bike on it; I had to actually use the Tow Mode (OD Off) with the bigger trailer. Oh, and my bike only weighs in at about 435 pounds.

Oh, and I'm running 35 KM2s at about 30psi.

[Toolman]

After the head replacement, I have an oil leak coming from somewhere.. 2012 JKUR

this is for sale

no confidence in jeeps built after 1998

[Tumbleweed13]

After the head replacement, I have an oil leak coming from somewhere.. 2012 JKUR

this is for sale

no confidence in jeeps built after 1998

Come on Mike. I wouldn't even say you have confidence in a 98 TJ. How much of your drive train is 98 jeep?