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Old 03-19-2014, 11:44 PM   #1
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Should i Re-Gear?

I drive a 2 dr Jk X. Running a 3 inch Rancho Lift kit with 35 inch tires. When I run out of freak (hopefully no sooner than a year) I plan to go to 37s. Needless to say, my MPG sucks. I run about 2500 rpm at 45 mph. I'm running stock gears; should I re gear?

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Old 03-20-2014, 12:50 AM   #2
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What year is your Jeep?

You'll want to re-gear for 37's. 3.73 is borderline for 35's with the 3.6. More liveable if you use a programmer to adjust for tire size (procal or flashcal).

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Old 03-20-2014, 01:16 AM   #3
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All gear questions can be answered by the gear ratio chart.

Pick your tire size and 70 MPH cruising RPM and you it gives the right gear ratio. If your current ratio is close enough then it may be not be worth upgrading.
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Old 03-20-2014, 03:57 AM   #4
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I drive a 2 dr Jk X. Running a 3 inch Rancho Lift kit with 35 inch tires. When I run out of freak (hopefully no sooner than a year) I plan to go to 37s. Needless to say, my MPG sucks. I run about 2500 rpm at 45 mph. I'm running stock gears; should I re gear?
Of course you do.
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Old 03-20-2014, 10:29 AM   #5
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For 37's and the older 3.8 V6, you'll be unhappy if you don't regear. Regardless, your MPGs are going to suck when you run 37s no matter what you do.
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Old 03-20-2014, 11:22 AM   #6
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X2 on all the above. The chart is great but only focuses on one speed. Use Derf's calculator (above)- I found it much more useful. You can calculate pretty closely to 45 MPH like you're asking. And your MPG with 37s is gonna suck like he says- there is no magic ratio that's guaranteed to fix that. I'd pick based on what you want- not what's best for MPG.
Year? Current ratio? We're all assuming you're running 3.21s or 3.73s.
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Old 03-20-2014, 11:30 PM   #7
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Thanks guys! Very helpful!
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Old 03-20-2014, 11:48 PM   #8
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For 35s, you should regear to 4.56 (some would say 4.88 ). For 37s, you would want 4.88 or 5.13.
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Old 03-21-2014, 04:42 AM   #9
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Personally, I would find others with tires and gears your looking for maybe test drive their rigs..,

The problem is, say you go 4.56 you will be wishing you went 4.88, or 5.13.. Lots of people love to "theory Craft" and decide for you.

best advice, once its done, your kind of stuck, so make sure.

I was waffleing between 4.88 and 5.13, I went 5.13, .... 4.88 on 35's would have prob. been fine, but 5.13 on trials/rocks is always better than 4.88. just my .02 its all in what your looking for, and the balance your needing.

For me, i gave up some gas mileage for better crawl speed, but thats what I was looking for, and i dont do much hwy driving. decide whats in YOUR best interest.
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Old 03-21-2014, 05:20 AM   #10
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Personally, I would find others with tires and gears your looking for maybe test drive their rigs..,
^ Good advice. A friend of mine at work drove mine the other day for exactly this reason.
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Old 03-21-2014, 06:45 AM   #11
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Personally, I would find others with tires and gears your looking for maybe test drive their rigs..,

The problem is, say you go 4.56 you will be wishing you went 4.88, or 5.13.. Lots of people love to "theory Craft" and decide for you.

best advice, once its done, your kind of stuck, so make sure.

I was waffleing between 4.88 and 5.13, I went 5.13, .... 4.88 on 35's would have prob. been fine, but 5.13 on trials/rocks is always better than 4.88. just my .02 its all in what your looking for, and the balance your needing.

For me, i gave up some gas mileage for better crawl speed, but thats what I was looking for, and i dont do much hwy driving. decide whats in YOUR best interest.
Why is 5.13 better with 35s? What would it do better? I am putting together my plan to grow up my Jeep, and my helper (who actually knows what he is doing unlike me!) said probably 4.88 would be be best (35s on 2.5 lift with flat fenders). We do play on rocks-in Phoenix that is about all we have other than mall parking lots lol. I have a Sport now with 3.73-he also says I should truss and reinforce the front axle and beef up I think the C-things. And while I am in doing the gears to add a rear locker. So what would 5.13 gain me? I do not plan to crawl the "big boy" trails (we will use his big boy Jeep for that lol), but just want a little more under me to open up more lines on mid/moderate level trails.
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Old 03-21-2014, 06:52 AM   #12
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5.13 will crawl slower And when crawling slower is better. Over all. Just my .02. 4.88 will be just fine. I picked 5.13 cause I don't have a Rubi transfer case so I wanted to go as small as possible The diff between 4.88 and 5.13 is not a lot , but after talking to several seasoned jeep buddies in my club that went 4.88 and some went 5.13. I just decided to go down that path. So far I love them. Super slow
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Old 03-21-2014, 07:01 AM   #13
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Personally, I would find others with tires and gears your looking for maybe test drive their rigs..,

The problem is, say you go 4.56 you will be wishing you went 4.88, or 5.13.. Lots of people love to "theory Craft" and decide for you.

best advice, once its done, your kind of stuck, so make sure.

I was waffleing between 4.88 and 5.13, I went 5.13, .... 4.88 on 35's would have prob. been fine, but 5.13 on trials/rocks is always better than 4.88. just my .02 its all in what your looking for, and the balance your needing.

For me, i gave up some gas mileage for better crawl speed, but thats what I was looking for, and i dont do much hwy driving. decide whats in YOUR best interest.
+2, I went from 3.73s with 35s to 4.56 on 35s. Very noticeable positive change. Would probably do 4.88s if I did it again. I was concerned about going with the 4.88 in a D30. Would have been fine probably, but being a daily driver tip the scale for me to the 4.56s.

Definitely re-gear though, you'll love your jeep even more!
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Old 03-21-2014, 08:54 AM   #14
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+2, I went from 3.73s with 35s to 4.56 on 35s. Very noticeable positive change. Would probably do 4.88s if I did it again. I was concerned about going with the 4.88 in a D30. Would have been fine probably, but being a daily driver tip the scale for me to the 4.56s.

Definitely re-gear though, you'll love your jeep even more!
So another question because I need to time all my "improvements" - cant have the heep sitting for days on end because well I still need to get to work. While I suspect not ideal, this tells me at least short term I could run 35s on my 3.73? Would I be confined to pavement or could I still run bunny trails? I would probably do the axle reinforcing stuff with the tires. Just how bad would it be short term? Or best to wait and just throw about $5-10k at my Jeep all at once and live with a rental for a while to get to work?
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Old 03-21-2014, 09:14 AM   #15
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2014 JKU 35's and 4:88's... Glad I did it.
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Old 03-21-2014, 09:20 AM   #16
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I ran 3.21 on 35's for 8months. i did put front gussests on the front because of the smaller axle, thats a given because of the added weight. but on 3.73 35's you can do a bit more than bunny trials.

I like doing upgrades then playing with them for a while.

honestly, your best upgrade is "seat time" no matter the wheel/gears/..whatever..
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Old 03-21-2014, 09:38 AM   #17
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I ran 3.21 on 35's for 8months. i did put front gussests on the front because of the smaller axle, thats a given because of the added weight. but on 3.73 35's you can do a bit more than bunny trials.

I like doing upgrades then playing with them for a while.

honestly, your best upgrade is "seat time" no matter the wheel/gears/..whatever..
Thanks! So long as I beef up the axles my Jeep wont self-destruct on 35s and I could still play with it. Will keep that in mind as I finalize the plan.

I ran a few trails already and that is what told me I need a few more inches-I was awesomely impressed and was the only true stock Jeep on the trails down to my tires (and these were mid/moderate level trails not gravel roads) and made it relatively unscathed. The only issue was that lack of clearance limited some of my lines-which is what my new shoes will address. I sort of took the girl Jeep back to pavement princess for a while until I can get new shoes figuring my luck would run out at some point and I would crunch something important.
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Old 03-21-2014, 09:58 AM   #18
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So another question because I need to time all my "improvements" - cant have the heep sitting for days on end because well I still need to get to work. While I suspect not ideal, this tells me at least short term I could run 35s on my 3.73? Would I be confined to pavement or could I still run bunny trails? I would probably do the axle reinforcing stuff with the tires. Just how bad would it be short term? Or best to wait and just throw about $5-10k at my Jeep all at once and live with a rental for a while to get to work?
My regear and lockers was a 2 day job.

As far as running 3.73 gears with 35s, some do it. Only you can really judge if it's tolerable.
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Old 03-21-2014, 08:56 PM   #19
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2014 JKU 35's and 4:88's... Glad I did it.
Which tranny? How is it on the highway?
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Old 03-22-2014, 12:50 AM   #20
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My regear and lockers was a 2 day job. As far as running 3.73 gears with 35s, some do it. Only you can really judge if it's tolerable.
I've been doing it for the last year. It's tolerable. I'm just not satisfied with tolerable.
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Old 03-22-2014, 08:27 AM   #21
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Did you reprogram your computer with a ProCal or whatever yet? I'm not sure if you drive an automatic, but that's recommended so the computer will know to change the shift points. The Jeep will feel a little better once that's done.
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Old 03-24-2014, 04:12 PM   #22
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Thanks guys! Been very helpful! I'm going to keep doing research and hold off for a little while longer as I scrape up some more cash.
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Old 03-24-2014, 04:24 PM   #23
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But if I re gear, are there any majorly essential upgrades that absolutely HAVE to go with it?
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Old 03-24-2014, 04:48 PM   #24
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But if I re gear, are there any majorly essential upgrades that absolutely HAVE to go with it?
While not 100% vital, it makes good sense to install lockers when you regear, assuming you want to put them in.

A full case locker has to be installed exactly the same way as the new gears. If you do both at the same time, you only pay for the labor once. Granted, you don't have to set the pinion depth the second time. But still. Taking apart everything else and installing the locker correctly takes up over half the time anyway.

If you want to do gears and lockers it pays to save up and do it all at the same time. Even if you have to wait a year to get the money scrounged up, it's worth it.

Swapping in chrome molly axle shafts is also easier if you do it when you install the gears. It doesn't take as much to install them later as it does to install the lockers but it's just easier since you already have it all the way apart.

I drove my JK with the 3.21 gears for a year while I saved up for lift, lockers, gears, chrome molly shafts, and tires all at once (along with a weld-on axle truss for the front D30). It was two very long weekends to get it all installed but when I was done it was all worth it.
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Old 03-24-2014, 04:50 PM   #25
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But if I re gear, are there any majorly essential upgrades that absolutely HAVE to go with it?
It's a Jeep my friend. Not "have", WANT. ; )
You can simply do a regear and regain your performance. Add a Procal for programming the gear ratio and you're done. Nothing else you have to have.
Anything else is icing on the cake/"while you're in there" modifications. Better pricing because the tech is already working on the carrier/pumpkin/gears. Vs. if you want to add a locker later you're paying for the full labor costs again.

Make that an X2 for Derf. Posted at the same time.
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Old 03-24-2014, 04:57 PM   #26
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Did you reprogram your computer with a ProCal or whatever yet? I'm not sure if you drive an automatic, but that's recommended so the computer will know to change the shift points. The Jeep will feel a little better once that's done.
should I have done that right after the lift and tires?
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Old 03-24-2014, 05:47 PM   #27
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I drive a 2 dr Jk X. Running a 3 inch Rancho Lift kit with 35 inch tires. When I run out of freak (hopefully no sooner than a year) I plan to go to 37s. Needless to say, my MPG sucks. I run about 2500 rpm at 45 mph. I'm running stock gears; should I re gear?
2500 rpm @ 45mph? That doesnt sound right???

With 37's your going to want at least 4.88. Your MPG is still going to suck.

With 5.13's I run 65mph @ 2500 rpm. 70mph @ 2800 rpm

@45 mph I am at maybe 1800 rpm when the OD kicks in.
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Old 03-24-2014, 07:51 PM   #28
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2500 rpm @ 45mph? That doesnt sound right??? With 37's your going to want at least 4.88. Your MPG is still going to suck. With 5.13's I run 65mph @ 2500 rpm. 70mph @ 2800 rpm @45 mph I am at maybe 1800 rpm when the OD kicks in.
yeah, I know. Once my OD kicks in, it's about 2000. I'm not going 37s until my 35s wear out, and they're basically brand new
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Old 03-24-2014, 08:51 PM   #29
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Just got my Jeep back from getting a re-gear and throwing in an Eaton E-Locker. Went from 3.21 to 4.10 but I've got the 33.8" Nitto Terra Grapplers. Two day job. Bought Procal to reprogram.

Seems to have more pick-up to it, but third gear stretches to 4000 plus RPM. Seems like it isn't shifting right.
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Old 03-24-2014, 10:06 PM   #30
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Just got my Jeep back from getting a re-gear and throwing in an Eaton E-Locker. Went from 3.21 to 4.10 but I've got the 33.8" Nitto Terra Grapplers. Two day job. Bought Procal to reprogram.

Seems to have more pick-up to it, but third gear stretches to 4000 plus RPM. Seems like it isn't shifting right.
Did you re-program for tire size and gear ratio? Also remember tire size for the procal is actual mounted/measured size, not what it says on the side wall.

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