Do Yourself a Favor - Regear Your 2012-Up JK!!

Draconianwinter said:
Personally, I don't care how the information is given to me if I am about to make a huge mistake with my jeep.

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There is no need to worry about regearing now. Just take these mods 1 step at a time. Determine what is important for you and start there, then 1 step at a time. Your jeep won't self-destruct.
 
I wanted to report that the 4.88's I just installed are perfect for "35's".

2015 JK automatic with 315 duratracs (33.75" tall with weight on them). RPM's are 2500@60 and 2850@70.

Take off from a stop is much improved. The jeep barely downshifts now where it used to need to kick down on every little uphill with the 4:10's.

My only worry is when I go to 37's in a few years, I'll probably wish I went 5.13, but I only have 12,000 miles on my tires so it'll be awhile.
 
zimm said:
I wanted to report that the 4.88's I just installed are perfect for "35's".

2015 JK automatic with 315 duratracs (33.75" tall with weight on them). RPM's are 2500@60 and 2850@70.

Take off from a stop is much improved. The jeep barely downshifts now where it used to need to kick down on every little uphill with the 4:10's.

My only worry is when I go to 37's in a few years, I'll probably wish I went 5.13, but I only have 12,000 miles on my tires so it'll be awhile.
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That's good to know, because the only thing I miss about the stock tires, is the way it drives on the road. I now have that aggravating kick down on a slight grade.


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zimm said:
I wanted to report that the 4.88's I just installed are perfect for "35's".

2015 JK automatic with 315 duratracs (33.75" tall with weight on them). RPM's are 2500@60 and 2850@70.

Take off from a stop is much improved. The jeep barely downshifts now where it used to need to kick down on every little uphill with the 4:10's.

My only worry is when I go to 37's in a few years, I'll probably wish I went 5.13, but I only have 12,000 miles on my tires so it'll be awhile.
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How did your gas mileage change?
 
It's too early to tell but on the ride home (55 miles) going 60mph computer showed 18 mpg when I got home. It's never been that high. Yes corrected with aev pro cal. Not having to kick down and rev out motor is probably helping. I'll report back after a tank. I was getting 12-13 hand calculated before with mixed driving. I hope I picked up a mpg.
 
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After 2 tanks of gas my MPG has settled in at 13.6 for mixed driving- I have a 12 mile commute that's half highway, half stop and go, and about a mile of gridlock. It does drive a hell of lot better though. Shift quicker, fast off the line, etc. The only "negative" if you can call it that is that it takes several long seconds for the tranny to get up into 5th on the highway, but that's just a nit-pick. It downshift a lot less when driving too. What a great mod!
 
zimm said:
After 2 tanks of gas my MPG has settled in at 13.6 for mixed driving- I have a 12 mile commute that's half highway, half stop and go, and about a mile of gridlock. It does drive a hell of lot better though. Shift quicker, fast off the line, etc. The only "negative" if you can call it that is that it takes several long seconds for the tranny to get up into 5th on the highway, but that's just a nit-pick. It downshift a lot less when driving too. What a great mod!
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Thanks for the update
 
I've posted about this in my build thread, but this great thread deserves a bump. Wayoflife is right. Oh what a difference!

I have a 2014 JKU Rubicon, with an automatic transmission, that came with 4.10 gears. After putting on 315/70r17 Goodyear Wrangler Duratracs, that measured about 33.75, and programming for the new tire size, with an AEV Procal, my rpm dropped to around 2450 at 70 mph. The 3.6L handled everything pretty well, but when driving in hills, the engine could not hold speed as well, without downshifting a lot more.

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Yesterday, I had my differentials regeared to 4.88. My current rpm at 70 mph, is right around 2900, or essentially 300 above stock rpm, with stock tires. The chart, here, seems very accurate.

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The 3.6L doesn't seem to be bothered at that rpm. It ran close to that, going 80 mph, before the regear. I may reduce my driving speeds, in the interest of fuel economy, but now I feel like the Jeep has its powerband back!

For your reference, my 60 mph rpm are about what 70 mph was with the metric 35's, and it doesn't shift as badly as it did.


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I too just got 4.88 installed 2015 3.6 manual what a difference from 3.21 with 315-70-17 great power never new the 3.6 was this good now just cant wait to get out and wheel it
 
jeepdave15 said:
I too just got 4.88 installed 2015 3.6 manual what a difference from 3.21 with 315-70-17 great power never new the 3.6 was this good now just cant wait to get out and wheel it
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I'm pretty pleased, that I skipped 4.56, and went 4.88. If I lose any gas mileage, I'll just chalk that up to the cost of having fun! [emoji2]


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