2012 w/ 5.13, my thoughts after my road trip.
12-27-2011, 01:57 PM
#1
JK Enthusiast
Thread Starter
2012 w/ 5.13, my thoughts after my road trip.
Just thought I'd post this for any new 2012 guys that are thinking of regearing. I still wish I'd gone with 4.88, especially after averaging 13mpg (@ 77mph avg speed). I drove from Denver to Lawrence, KS and averaged about 13mpg on I-70 with the 5.13 on 37s with auto trans. The 200-300 rpms you would drop by having 4.88 IMO would make a significant change in the mileage. After 5000 miles with the Pentastar and 37s combo I'd recommend:
5.38 (Rubicons) - Trail only, auto only. ***manual trans will rev, clutch dump and grenade the D44 diff with this HP. You will blow it up, just a matter of time.***
5.13 - Drivers that mostly town and trail drive.
4.88 - Drivers that drive a fair amount of hwy and want a good gear ratio for all types, including trail.
4.56 - Drivers that make significant trips on the highway with regularity, but still tool around on moderate offroad trails.
This being said, I make 2-3 trips a year back to the KC area and I just prefer to drive my Jeep rather than her car, and I really do wish I'd installed the 4.88. The Pentastar has good power, enough to spare without killing offroad performance by going to a 4.88.
The new Jeeps just don't compare to the 3.8L guidelines for gearing. Apples and Oranges.
5.38 (Rubicons) - Trail only, auto only. ***manual trans will rev, clutch dump and grenade the D44 diff with this HP. You will blow it up, just a matter of time.***
5.13 - Drivers that mostly town and trail drive.
4.88 - Drivers that drive a fair amount of hwy and want a good gear ratio for all types, including trail.
4.56 - Drivers that make significant trips on the highway with regularity, but still tool around on moderate offroad trails.
This being said, I make 2-3 trips a year back to the KC area and I just prefer to drive my Jeep rather than her car, and I really do wish I'd installed the 4.88. The Pentastar has good power, enough to spare without killing offroad performance by going to a 4.88.
The new Jeeps just don't compare to the 3.8L guidelines for gearing. Apples and Oranges.
12-27-2011, 02:18 PM
#2
JK Enthusiast
Thread Starter
cant you just use a set off 33s or stockers when traveling distance ? would that work ? im not that familiar with gearing ! i have 33s on my 410s and get 17 ` 19 mpg on straight runs but if i want great milage id have my stock ones put back on for a long run ! 22 or 23mpg 
im not sure if that works with that gearing at all ! thats why im leaving mine prety much stock ! best of both worlds !
im not sure if that works with that gearing at all ! thats why im leaving mine prety much stock ! best of both worlds !
12-27-2011, 02:31 PM
#3
JK Enthusiast
Thread Starter
theres a price to pay for going big !
12-27-2011, 03:55 PM
#5
JK Enthusiast
Thread Starter
It is really hard to get good fuel economy in a loaded down jeep at an average 77 mph regardless of gearing. With that average, you probably spent some time over 80 mph.
At 70 mph ave instead of 77 mph, and with tire psi maybe 3-5 lbs higher, I'd bet you would see an increase from 13 to as much as 17.
I'd agree with the observations on the 2012 automatic with the exception that slowing down a little compromises a little extra travel time in exchange for better offroad and in-town performance.
I wouldn't agree that 5.38s would end up blowing up the gears off road as a certainty. Just the opposite, with a lower crawl ratio, you dump the clutch less frequently. What blows 5.38s offroad is a combination of bouncing through obstacles with tire spin/sudden traction situations.
At 70 mph ave instead of 77 mph, and with tire psi maybe 3-5 lbs higher, I'd bet you would see an increase from 13 to as much as 17.
I'd agree with the observations on the 2012 automatic with the exception that slowing down a little compromises a little extra travel time in exchange for better offroad and in-town performance.
I wouldn't agree that 5.38s would end up blowing up the gears off road as a certainty. Just the opposite, with a lower crawl ratio, you dump the clutch less frequently. What blows 5.38s offroad is a combination of bouncing through obstacles with tire spin/sudden traction situations.
As for the clutch dump, I'm talking about average drivers not used to that sort of torque, caught on big hills, panicking and dumping it at 5k rpm. Kaboom. Of course you won't blow it up if you're already in gear and crawling. The 5.38 would just be massive overkill if it ever touches pavement. Totally unnecessary unless you trailer it. My 2009 was 5.38 and just fine, but I wouldn't EVER gear the 3.6L to 5.38 without running 40s, just not needed at all.
12-27-2011, 04:41 PM
#6
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I can see that being low when 4.88 gears with 35" tires would get you about back to stock being similar to 4.10 gears and 32 inch tires. 40's would put you back to stock as well ratio-wise, but it might be tough on axles and drivetrain.
12-27-2011, 05:42 PM
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Just thought I'd post this for any new 2012 guys that are thinking of regearing. I still wish I'd gone with 4.88, especially after averaging 13mpg (@ 77mph avg speed). I drove from Denver to Lawrence, KS and averaged about 13mpg on I-70 with the 5.13 on 37s with auto trans. The 200-300 rpms you would drop by having 4.88 IMO would make a significant change in the mileage. After 5000 miles with the Pentastar and 37s combo I'd recommend:
5.38 (Rubicons) - Trail only, auto only. ***manual trans will rev, clutch dump and grenade the D44 diff with this HP. You will blow it up, just a matter of time.***
5.13 - Drivers that mostly town and trail drive.
4.88 - Drivers that drive a fair amount of hwy and want a good gear ratio for all types, including trail.
4.56 - Drivers that make significant trips on the highway with regularity, but still tool around on moderate offroad trails.
This being said, I make 2-3 trips a year back to the KC area and I just prefer to drive my Jeep rather than her car, and I really do wish I'd installed the 4.88. The Pentastar has good power, enough to spare without killing offroad performance by going to a 4.88.
The new Jeeps just don't compare to the 3.8L guidelines for gearing. Apples and Oranges.
5.38 (Rubicons) - Trail only, auto only. ***manual trans will rev, clutch dump and grenade the D44 diff with this HP. You will blow it up, just a matter of time.***
5.13 - Drivers that mostly town and trail drive.
4.88 - Drivers that drive a fair amount of hwy and want a good gear ratio for all types, including trail.
4.56 - Drivers that make significant trips on the highway with regularity, but still tool around on moderate offroad trails.
This being said, I make 2-3 trips a year back to the KC area and I just prefer to drive my Jeep rather than her car, and I really do wish I'd installed the 4.88. The Pentastar has good power, enough to spare without killing offroad performance by going to a 4.88.
The new Jeeps just don't compare to the 3.8L guidelines for gearing. Apples and Oranges.
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12-27-2011, 06:23 PM
#10
JK Freak
i agree. my only mod is a 2" lift, still stock tires and got 20 mpg on the highway with 4:10s. awesome performance off road too, no reason at all to regear with stock tires and probably not with 33s or even 35s with the auto. the first 3 gears in the auto are a lot lower than previous years, and the 5th gear OD is also lower - meaning lower crawl ratio but also higher rpms at speed than the previous autos.
Last edited by bbolander; 12-28-2011 at 03:28 AM.