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2010 JKU 3.8L auto w/ 35s - 5.13s to low??

Old 03-09-2018, 12:16 PM
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Default 2010 JKU 3.8L auto w/ 35s - 5.13s to low??

I'm regearing my JKU. It's a 3.8L automatic, and my daily driver.

I currently have 35s on it, but want to regear for 37s.

I've researched this high and low and can't find a definitive answer.

I was planning on 5.13s, but I'm worried that may be too low of a gear. 95% of my driving is city/county with the occasional 55mph 2 lane highway. Rarely ever see the interstate.

Just looking for real world experience before I do something I'll regret

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Old 03-09-2018, 12:27 PM
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You will get different opinions, but mine is that : 5.13 is absolutely not too low for 35's with a 3.8 auto. I ran 5.13 with 33's for a few months until I got 35's. Then 5.38's with the 35's for a while before finally going to 37's. I think these 3.8 auto's run better with higher rpm's.

The downside will be the pinion size on that d30. (assuming you do not have a rubicon). Manageable, but some are concerned about it.

There are plenty of charts floating around, but assuming a 34" actual measured tire height, you would be looking at:

2450 rpm at 70. (35's that measure 34")
2313 rpm at 70. (37's that measure 36")

Certainly nothing close to "you'll have screaming high rpm's!!!" that you see some people rant about. If anything, you'll probably be kicking yourself for not going to a front 44 and 5.38's ...

Last edited by nthinuf; 03-09-2018 at 12:36 PM.
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Old 03-10-2018, 05:13 PM
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I agree. With the 3.8/automatic, 5.13's are about perfect for 35's. But they are not low enough for 37's.
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