Auto and 35's
JK Super Freak
Joined: Mar 2007
Posts: 1,441
Likes: 1
From: Gilmanton Iron Works, NH
I've got an 07 JKU with auto, 4.10s and 35s. In addition to that, it is heavily armored. No problem. I was going to regear before I put my Rubi t-case in but now I'm not so sure. 
JK Enthusiast
Joined: Oct 2010
Posts: 216
Likes: 0
From: St. Louis, MO
5.13s w/35s in my auto JKU Rubi seem to be just right. Feels peppier off the line than the stock 4.10s w/32s. Anxiously awaiting the SuperChips tunes for the 2011 so I can get even a bit more of a boost...
JK Enthusiast
Joined: Nov 2010
Posts: 228
Likes: 0
From: RSM, Ca
I have 4:10s and 35s. I superchipped for performance tune. Noticed some improvement. I also noticed an advanced tune that changes up/down shift rpms. Do I have to go advanced tune route to get what your getting or does the standard perf tune pretty much get you there?? Thanks
JK Enthusiast
Joined: Oct 2010
Posts: 202
Likes: 0
From: Youngstown
I have to do this too and it makes a huge difference. I drive highway about 40 miles one way to work and I bog down on every incline with OD on.
JK Enthusiast
Joined: Feb 2010
Posts: 205
Likes: 0
From: Albemarle, NC
Bite the bullet and get 5.13's. I had auto, 4.10s and 35's for about a year and it aggravated the crap out of me. Now with my regear i can maintain speed on most inclines and not constantly shifting out of OD. My fuel mileage went from 14ish to 17ish. I have a hypertech max energy so I am calibrated. I wish I would have regeared the day I bought my JK U
JK Super Freak
Joined: Aug 2008
Posts: 1,799
Likes: 1
From: Seattle, WA
Bite the bullet and get 5.13's. I had auto, 4.10s and 35's for about a year and it aggravated the crap out of me. Now with my regear i can maintain speed on most inclines and not constantly shifting out of OD. My fuel mileage went from 14ish to 17ish. I have a hypertech max energy so I am calibrated. I wish I would have regeared the day I bought my JK U
JK Junkie
Joined: Sep 2010
Posts: 2,215
Likes: 0
From: Scottsdale, AZ
I've been running 35's for a week now on my auto with 3.73. I can't tell you the actual gas mileage yet, but after using half a tank, I don't think it will have changed much from my stock tires. The speedometer is 10% off so I have to recalibrate eventually, but no big deal. I drive her to work every day about 40 miles round trip highway and side streets and haven't noticed much difference...at least not enough to make me crazy.
JK Jedi Master
Joined: Jan 2008
Posts: 11,463
Likes: 165
From: Austin <--> Colorado Springs
It's not magic or a big secret or anything. Turn OD Off and you bring your rpm's up to a liveable level.
Measure your tires, then plug the number into the chart in the FAQ's. That gives you the OD On rpm at 70. Divide that number by .69 to get the OD off rpm.
Auto, 4.10's -
stock 32's = 2150 rpm @ 70
new 35's = 1950 rpm @ 70
35's OD Off = 2825 rpm @ 70
new 37's = 1850 rpm @ 70
37's OD Off = 2680 rpm @ 70
The negatives are that:
When you downshift, you are dropping down into 2nd gear. This raises the rpm's considerably higher than being properly geared and downshifting from 4th to 3rd.
And you lose your low end. You will find that to go up steeper hills, you will 'have' to go into 4lo for the gearing just to keep moving forward.
Neither are huge issues, just things to be aware of.
Measure your tires, then plug the number into the chart in the FAQ's. That gives you the OD On rpm at 70. Divide that number by .69 to get the OD off rpm.
Auto, 4.10's -
stock 32's = 2150 rpm @ 70
new 35's = 1950 rpm @ 70
35's OD Off = 2825 rpm @ 70
new 37's = 1850 rpm @ 70
37's OD Off = 2680 rpm @ 70
The negatives are that:
When you downshift, you are dropping down into 2nd gear. This raises the rpm's considerably higher than being properly geared and downshifting from 4th to 3rd.
And you lose your low end. You will find that to go up steeper hills, you will 'have' to go into 4lo for the gearing just to keep moving forward.
Neither are huge issues, just things to be aware of.