4.56 or 4.88 gears w/ 35" Tire on a 2012 JKU RUbicon Automa ?
03-23-2012, 09:52 AM
#11
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Not surprised at all on this. Early on with the JKs they were ran out of 4.88s and 5.13s and the 4.56s were so unpopular there wasn't a production run of them. That basically leaving the choice of 4.88s and 5.13s. That's the point where the 4.88s for manuals and 5.13s for autos was born although it didn't totally wash.
I hope that the run on 4.56s opens someone's eyes to a need for 4.30s.
I hope that the run on 4.56s opens someone's eyes to a need for 4.30s.
03-23-2012, 10:03 AM
#12
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It is decision time on which gears for my daily driver 2012JKU Rubicon with the Automatic transmission. I put a 3" Teraflex lift on to fit 35" Toyo M/T's. That coupled with the front and rear bumpers, winch, and skid plates seem to have made for a very heavy JKU. Around town (San Diego) it drives just fine and gets up to speed on the highway just fine - not a peppy as it used to be, but acceptable. However, when I go up a hill it has to dig deep into the gears and has difficulty maintaining speed. At 70mph, the tach reads around 21K. It will get up to 26k if the road goes up a grade. MPG also sucks ~13mpg.
The charts would indicate that a 4.56 gear swap is in order. When I scheduled the work, the shop strongly encouraged me to use 4.88s. This has me dithering. One reason put forth is that the evolution path of jeep owners inevitably leads to 37" tire. Frankly, I do not see this happening. My primary goal is to get it back to speed on the hills and I am hoping that some of the poor gas mileage is due to lugging. I plan on several off-road trips per year and am currently getting ready for the EJS. Looking for advise.
Thanks!
gjoyce3
The charts would indicate that a 4.56 gear swap is in order. When I scheduled the work, the shop strongly encouraged me to use 4.88s. This has me dithering. One reason put forth is that the evolution path of jeep owners inevitably leads to 37" tire. Frankly, I do not see this happening. My primary goal is to get it back to speed on the hills and I am hoping that some of the poor gas mileage is due to lugging. I plan on several off-road trips per year and am currently getting ready for the EJS. Looking for advise.
Thanks!
gjoyce3
Did you try using a programmer for your jeep to get your shift points back in the right spots??? With the power this thing has there shouldnt be a need to re gear. Not at least till 37's
03-24-2012, 06:23 PM
#13
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I have reprogrammed with an AEV unit and around town it is OK (meaning generally level driving). It is the going up hills and starting out on inclines that causes the Jeep to reach deep. Also, there seems to be resistance to maintaining highway speed (not sure how to describe it other than that). Admittedly, I put the heaviest tires on that I could and I suspect that coupled with the added weight of front/rear bumpers; winch; EVO skid plates, and a full size spare are what puts the damper on my get up and go.
BTW - where is my beer?
gjoyce3
BTW - where is my beer?
gjoyce3
04-21-2012, 04:05 AM
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I am holding out for 4.56's. The stock 4.10's got me to Moab and back. Generally, the 4.10's are acceptable - pick-up is fine with no problems passing, but going up the mountains in 3rd gear got old and really cemented my desire to upgrade. I got pretty close to 15MPG on flat or downhill highway stretches, dropping to 13 in the mountains.
In the meantime, she has been in the shop getting a new header due to a cylinder 6 misfire which started the day before I left for Moab :( Dealer told me it would be fine to use for a week and they were right
Took two weeks to get the part (apparently very much in demand). Just got her back today. I will start calling around for the gears next week and will follow up when installed.
gjoyce3
In the meantime, she has been in the shop getting a new header due to a cylinder 6 misfire which started the day before I left for Moab :( Dealer told me it would be fine to use for a week and they were right
Took two weeks to get the part (apparently very much in demand). Just got her back today. I will start calling around for the gears next week and will follow up when installed.gjoyce3
04-21-2012, 05:21 AM
#17
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Go with 4.56...I am running them in my 2012 JKU Rubi and love the set up. At the time Superior was the only manufacture that was making the 4.56 and I found them at Quadratec. I feel 4.88 would have been a little steep for the new engine, pre-2012 4.88 or 5.13 all the way. Oh and I am getting 17 mpg running 35's.
04-23-2012, 12:21 PM
#18
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Go with 4.56...I am running them in my 2012 JKU Rubi and love the set up. At the time Superior was the only manufacture that was making the 4.56 and I found them at Quadratec. I feel 4.88 would have been a little steep for the new engine, pre-2012 4.88 or 5.13 all the way. Oh and I am getting 17 mpg running 35's.
02-22-2013, 03:12 PM
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I have a 2008 with a 6-speed manual which I put 4.88 gears on and it was a crazy difference from the original 3.21 gears. Now I'm back to 4.56.
I was in 6th gear at like 45 mph. Due to a weird crazy incident with a dealearship - I ended up taking my Jeep back to the shop and getting 4.56 gears. They were just put on yesterday so I don't have RPM versus mph comparisons yet plus I have to ensure my speedo is set correctly as my SuperChips isn't ever accurate if I just set the tire size for some weird reason. But I will post that info later if you like.
In a day of driving have barely noticed a difference between 4.88 and 4.56 gears when it comes to torque and/or power, but I got first gear back (barely usable before and skipped first gear often) and it seems like I can use all my gears better now. It is only day 1 though...
I was in 6th gear at like 45 mph. Due to a weird crazy incident with a dealearship - I ended up taking my Jeep back to the shop and getting 4.56 gears. They were just put on yesterday so I don't have RPM versus mph comparisons yet plus I have to ensure my speedo is set correctly as my SuperChips isn't ever accurate if I just set the tire size for some weird reason. But I will post that info later if you like.
In a day of driving have barely noticed a difference between 4.88 and 4.56 gears when it comes to torque and/or power, but I got first gear back (barely usable before and skipped first gear often) and it seems like I can use all my gears better now. It is only day 1 though...