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Old 06-19-2013, 07:42 PM   #1
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JK Tires Size

What size tires can I put on my 2008 4-door JK without affecting the engine/transmission shifting in and out of overdrive excessively? I own the 6 cylinder automatic. I have a 3 inch lift.

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Old 06-19-2013, 07:53 PM   #2
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like 33ish if it came with 31 inch tires stock(the ones with the 17" aluminum wheels). 31ish if it came with 29s(the 16" stamped steel wheels) but really man you should get a procal at least, it'll pay for itself in gas and transmission life, as well as give you an accurate mpg reading and speedometer.

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Old 06-19-2013, 07:56 PM   #3
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Besides, you could then go to 35 inch tires which, based on my experience, is the minimum worth upgrading to! Especially in your 4 door which has less of a breakover angle anyway.

After that it would be limited mainly by axle strength, stock Dana 44s could get you up to a 37 but after that you're going to need reinforcements!
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Old 06-19-2013, 08:01 PM   #4
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Without regearing? 33's The auto that came with the 3.8 is a DOG. 35s behind that setup without a regear SUCKS.
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Old 06-19-2013, 08:16 PM   #5
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Thanks I have 18 inch stock rims. Will look at the 33s. i do have an AEV Procal.
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Old 06-21-2013, 10:29 PM   #6
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okay the off road shop put on NItto 35/12.5/18 and i am not happy. i am having problems with the high rpms and constant in and out of over drive. When questioned about these tires the tech said this is what we put on all the jeeps. i have 2008 JK 6 cyl automatic
I need some help here. I have 30 day exchange/store credit
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Old 06-21-2013, 11:13 PM   #7
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Originally Posted by shotan View Post
okay the off road shop put on NItto 35/12.5/18 and i am not happy. i am having problems with the high rpms and constant in and out of over drive. When questioned about these tires the tech said this is what we put on all the jeeps. i have 2008 JK 6 cyl automatic
I need some help here. I have 30 day exchange/store credit
Your tech is no good. The pre 2012 auto trans jeeps don't do well with larger tires. Look up jeep 42rle transmission and you should find a lot of good info from the TJ crowd. The only way you and straighten it out is to re gear.
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Old 06-21-2013, 11:17 PM   #8
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Without regearing? 33's The auto that came with the 3.8 is a DOG. 35s behind that setup without a regear SUCKS.
Yes regearing is the way to go. I'm regeared to 4.56 with the pentastar. From what I've been told, JKs with the 3.8s are best regeard to about 4.88 with 35s.

OP - although a regear would help with acceleration and smoothness, you really shouldn't have an issue with abnormal shifting and such. Be sure to double check the procal settings, if the shop did it, they might have messed it up. Use a speedometer app driving down a straight road to double check your Jeep's spedometer. Keep in mind that tires labeled at 35" might actually run about 34.5 when on your Jeep. Start there, and then if you can't get it to behave, I would regear to about 4.56-4.88. What stock gear ratio did your differentials come with?
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Old 06-23-2013, 01:18 PM   #9
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i have the 3:73 stock gears
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Old 06-23-2013, 01:53 PM   #10
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Dang I'm really sorry to hear that, man.
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Your tech is no good. The pre 2012 auto trans jeeps don't do well with larger tires. Look up jeep 42rle transmission and you should find a lot of good info from the TJ crowd. The only way you and straighten it out is to re gear.
Good point, I heard that the pre-12 trannys and engines are a little under-engineered for large tires but you'd still think that with 3.73, 35s would be drivable. While I was waiting to save up for the regear, I ran with my 3.21 gears and 35s for quite a while with no issues. I guess the tranny and engine improvements for the 12s made the difference, hell my wife actually wheeled with her '12 on 33s with 3.21 gears a couple times with no issues.

OP - I don't know if you have any experience with regearing. I'm like 99.99 percent sure that the carrier for the 3.73 gears is compatible with 4.56 gears, so it shouldn't cost that much to regear if you have a buddy who does it or you're willing to take on the task yourself. I went from 3.21s which required a new carrier so it was a bit pricey.
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Old 06-23-2013, 02:01 PM   #11
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Here you go as to how big overall: Largest tire on stock JK? Here's your answer!

As to the gearing issue, yeah, you need new gears unless you don't mind it being a dog.
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Old 06-24-2013, 06:41 PM   #12
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thanks for all the info you would think a 4x4 shop would tell you the max staying on stock gears or to regear. such a pain
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Old 06-24-2013, 06:46 PM   #13
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Some people just deal with it, some re-gear. Re-gearing would be the preferable method.
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Old 06-25-2013, 08:47 PM   #14
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thanks for all the info you would think a 4x4 shop would tell you the max staying on stock gears or to regear. such a pain
Not all shops specialize in jeeps

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