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Old 07-18-2014, 09:28 PM   #1
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Gear Ratio Suggestions?

Hey all.

My 2012 2dr JK has the automatic and the 3.21 gears. Im running the stock 255/75-17 rims and tires.

Im going to run a 2"lift and step up slightly to the 285/75-17 wheel combo.

Should i do a gear change? If so to what ratio?

While i'm in there , i'm most likely going to put in True tracs or some kind of Limited Slip diffs at the same time.

Currently im getting btwn 18.5MPG in town and 24 on the fwy.

Ideas?????

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Old 07-18-2014, 10:11 PM   #2
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Man 3:73 or4:10s would be great for you but there more spendy than aftermarket gears. ie 4:56, 4:88s . Do you plan on heavier bumpers and stuff down the road ?
Trutracs are a good choice for LSD's.

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Old 07-18-2014, 10:19 PM   #3
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Yes, im gonna go with a Warn Full width, LOD full width or a Rock hard bumper and a warn Zenon. Most likely will get a tire carrier and a bumper in back eventually as funds allow. Its the wifes DD so i don't want MPG to slip tooooo much but want to keep some performance/ Get up and go.
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Old 07-19-2014, 02:03 PM   #4
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It's a tough call. 3.73s would be perfect for that combo, you can get used ones for 100 bucks. If you are adding trutracs front and rear it's a job worth doing. Probably going to cost you 2000 for parts and labor with used gears. You mileage wouldnt take too much of a hit. If you have any thought of larger tires dont go anything less than 4.56.
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Old 07-19-2014, 04:28 PM   #5
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Those are ~34" tires. You need 4.10 gears at minimum. As described above gears swaps are expensive so it's better to have slightly shorter gears in case you want larger tires.

Look at the 3.6 gear chart and pick the gears that best fit your fuel economy/performance needs.

Either way get ready to give up at least 1.0- 1.5 MPG.
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Old 07-19-2014, 06:47 PM   #6
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I personally wouldn't go with 3.73. I'd only go 4.10 and only if I was never going to go up in tire size. If I was even thinking of going to bigger tires, I'd go with 4.56 gears. Changing gears is expensive so do it with the long term plan in place. You don't want to have to do it twice.
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Old 07-19-2014, 07:23 PM   #7
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I've said it before, try it before you spend the money. I run 2.5 inch springs an 1 inch teraflex spacers with 305 - 70 -17 maxxis bighorns with 3:21 gears and it runs fine. I did use the pro cal module and like i said mine runs good
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Old 07-20-2014, 06:02 AM   #8
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Originally Posted by scapegoat32 View Post
I've said it before, try it before you spend the money. I run 2.5 inch springs an 1 inch teraflex spacers with 305 - 70 -17 maxxis bighorns with 3:21 gears and it runs fine. I did use the pro cal module and like i said mine runs good
I have the same exact configuration right down to the ProCal and I also would not consider a gear change.
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Old 07-20-2014, 06:10 AM   #9
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I run that size with 3.73 gears, it is okay but not optimal. I will be changing to 4.56 gears in About a year. I live in the hills and sixth gear is useless but what the real issue is with crawling speed, it's just too fast.
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Old 07-20-2014, 07:04 AM   #10
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I have a 14 with 285/75-17 4.10's and ~2 lift (RK 1.5) do yourself a huge money saving favor and skip the 285/75-17s and go right to some true 35's . 4.10's are perfect with the 285's but go 4.56's and with the money you save add that towards 35's.
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Old 07-20-2014, 09:29 AM   #11
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Should a gear be useless? I have 3.21 gears with stock 32's and when Im on the highway i cruise at 65mph still in 4th gear and my rpms are around 2700. I have a 6spd manual. Im looking to do 33's real soon. I know gear swap is real expensive so I will upgrade from 3.21 to 4.10 or 4.56. Going from 3.21 to 3.73 isn't worth it improving at least two sizes will be a noticed difference. Should I go 4.10 or 4.56. I do mostly street with mild trails.
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Old 07-20-2014, 12:49 PM   #12
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Quote:
Originally Posted by spinlock View Post
Those are ~34" tires. You need 4.10 gears at minimum. As described above gears swaps are expensive so it's better to have slightly shorter gears in case you want larger tires.
Look at the 3.6 gear chart and pick the gears that best fit your fuel economy/performance needs.
Either way get ready to give up at least 1.0- 1.5 MPG.
Agree with spinlock. My tires measure 33.75 and I have the 4.10 axle (automatic)... If I would have the 3.73 I would change to 4.56.
The 4.10 is a minimum with such tire... maybe consider a 315 and 4.56 combo...
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Old 07-20-2014, 01:01 PM   #13
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Originally Posted by Trendsetter75 View Post
Should a gear be useless? I have 3.21 gears with stock 32's and when Im on the highway i cruise at 65mph still in 4th gear and my rpms are around 2700. I have a 6spd manual. Im looking to do 33's real soon. I know gear swap is real expensive so I will upgrade from 3.21 to 4.10 or 4.56. Going from 3.21 to 3.73 isn't worth it improving at least two sizes will be a noticed difference. Should I go 4.10 or 4.56. I do mostly street with mild trails.
4.10 is fine, and 4.56 is not too much. I think the gear sets are cheaper for 4.56 than for 4.10. 4.56 will be ideal if you ever want to upgrade to 35's.
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Old 07-20-2014, 01:25 PM   #14
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When someone says "mine runs real good with 3.21 gears", ask yourself "compared to what?" I say that because earlier this year I sold a hemi Jeep for enough money to buy two brand new 2-door JKs. I kept one for myself and gave the other one to my son. The only differences between the two Jeeps is that mine has 3.21 gears and his has 3.73 gears. Other than that, and a different stereo system, the Jeeps are the same. His runs better; a lot better. Every time I get in his Jeep I think "this is a great little Jeep". Every time I get out of his Jeep, and get in my Jeep, I'm thinking "what is wrong with this Jeep?". The taller geared Jeep just doesn't want to move. I'm always having to push the gas pedal more on the 3.21 geared Jeep, and it isn't as much fun to drive. And this is with STOCK tires on both Jeeps. Throw a set of 34s on a 3.21 geared Jeep, and it is going to be a real dog, because they're a dog with stock tires on them.

I went with 4.56 gears in my Jeep, because I'm going to use 35" tires. In your situation, with 34" tires, 4.10 gears would be just right.
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Old 07-20-2014, 03:12 PM   #15
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Originally Posted by TerraSol View Post
Agree with spinlock. My tires measure 33.75 and I have the 4.10 axle (automatic)... If I would have the 3.73 I would change to 4.56.
The 4.10 is a minimum with such tire... maybe consider a 315 and 4.56 combo...
The OP has 285s, not 315s, 285s mounted run 31.75-32.50, and if it's a DD, then 4.56 is way too deep for him. Alloy USA and a few others have 4.10s for the D30, and if you don't catch the bug where it's never big enough, then some 4.10s would work (they are no more expensive than other gears)for 285/315s.
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Old 07-20-2014, 03:22 PM   #16
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Originally Posted by LVCapo View Post
The OP has 285s, not 315s, 285s mounted run 31.75-32.50, and if it's a DD, then 4.56 is way too deep for him. Alloy USA and a few others have 4.10s for the D30, and if you don't catch the bug where it's never big enough, then some 4.10s would work (they are no more expensive than other gears)for 285/315s.
285/75-17's run a true 33" when on the jeep and 34" when off the jeep, that is what I have.
There have been days I would have liked 4.56 vs my 4.10's and I run 80mph on the interstate often.
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Old 07-20-2014, 03:28 PM   #17
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285/75-17's run a true 33" when on the jeep and 34" when off the jeep, that is what I have.
There have been days I would have liked 4.56 vs my 4.10's and I run 80mph on the interstate often.
Please tell me what 285s run 34"? 33" installed?
Not trying to be argumentative but I've run Duratracs, Fun Country IIs, Coopers, Nittos Terra Grapplers in 285/70/17 flavor...and not a single one of them has measured 33"mounted on a moderate 2DR at 33-35PSI.
I'm currently running 315 ProComp MT2s with 3.73s and they measure a hair under 33.5" at 35PSI, get about 17.7 MPG and turn ~2200 at 70 MPH
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Old 07-20-2014, 03:33 PM   #18
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Toyo open country at2's. I think you might be thinking of 70's not 75's. I was not aware that duratrac or FC2's came in 285/75-17

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Old 07-20-2014, 03:36 PM   #19
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Toyo open country at2's. I think you might be thinking of 70's not 75's.

Good call......100% my bad

OP, what kind of driving do you do? What are your wheeling plans? I think that will help us help you
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Old 07-20-2014, 04:35 PM   #20
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Please tell me what 285s run 34"? 33" installed?
...
BF Goodrich KM-2 mud terrains. 33" exactly, listed at 33.9"
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Old 07-20-2014, 05:09 PM   #21
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BF Goodrich KM-2 mud terrains. 33" exactly, listed at 33.9"
Yeah, if you read the thread there was some confusion between 285/70/17 and 285/75/17...
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Old 07-20-2014, 05:24 PM   #22
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Yeah, if you read the thread there was some confusion between 285/70/17 and 285/75/17...
I did, in it you asked the following;

Quote:
Originally Posted by LVCapo View Post
Please tell me what 285s run 34"? 33" installed?
Not trying to be argumentative but I've run Duratracs, Fun Country IIs, Coopers, Nittos Terra Grapplers in 285/70/17 flavor...and not a single one of them has measured 33"mounted on a moderate 2DR at 33-35PSI.
I'm currently running 315 ProComp MT2s with 3.73s and they measure a hair under 33.5" at 35PSI, get about 17.7 MPG and turn ~2200 at 70 MPH
I then replied with my answer KM-2's, 285-75-17

The OP and jadmt were both refering to 285-75-17
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Old 07-20-2014, 06:38 PM   #23
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Good lord man.........
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Old 07-20-2014, 06:59 PM   #24
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Originally Posted by MOPWR2U View Post
When someone says "mine runs real good with 3.21 gears", ask yourself "compared to what?" I say that because earlier this year I sold a hemi Jeep for enough money to buy two brand new 2-door JKs. I kept one for myself and gave the other one to my son. The only differences between the two Jeeps is that mine has 3.21 gears and his has 3.73 gears. Other than that, and a different stereo system, the Jeeps are the same. His runs better; a lot better. Every time I get in his Jeep I think "this is a great little Jeep". Every time I get out of his Jeep, and get in my Jeep, I'm thinking "what is wrong with this Jeep?". The taller geared Jeep just doesn't want to move. I'm always having to push the gas pedal more on the 3.21 geared Jeep, and it isn't as much fun to drive. And this is with STOCK tires on both Jeeps. Throw a set of 34s on a 3.21 geared Jeep, and it is going to be a real dog, because they're a dog with stock tires on them.

I went with 4.56 gears in my Jeep, because I'm going to use 35" tires. In your situation, with 34" tires, 4.10 gears would be just right.
I have to agree with this post I have a 14 jku with 3.21 and 33" duratracs , mine is a manual so it's alittle better but you can def feel the power loss. I went from a 2011 mustang gt with about 550 hp to the jeep complete opposites lol and yes with 3.21 it's ok i still have 6th gear on the hwy but sometimes have to downshift if your gonna regear go 4.10 at minimum
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Old 07-20-2014, 07:09 PM   #25
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Ok so it's the wife's DD you want to keep mpg up, your getting bumpers winch, 2" lift. I would look into your crystal ball to see down the road mods,
ie bigger lift, bigger tires. It's an addiction man admit to it now you will feel better lol..I guess I'd seriously think about the 4:56s. Jeep on....

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