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Old 09-05-2019, 03:52 AM
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Differential advice.....

Have a 2006 Rubicon that was built (not by me) for off road. I'm wanting it to do some trail running, but also suitable for daily driving/road trips. It is currently running 5.13 differentials. I'm considering regearing to 4.56 or possibly even 4.27. It has 35 inch tires. I guess I'm asking which diff ratio would serve me best as both a trail runner (not rock crawler) and a highway driver? And I would lean a little more toward the highway driver in the consideration. Good on the highway, but capable on moderate off road trails.

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Old 09-05-2019, 05:06 AM   #2
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you're going to have to reveal what transmission you have for the gurus to weigh in, but generally speaking it sounds like you're probably already geared for optimum performance on & off road. Re-gearing to 4.56 would be an awfully expensive adventure to knock a few rmps off on the highway. This move isn't making much sense to me.

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Old 09-05-2019, 05:30 AM
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Sorry for the omission. It has a six speed manual.
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Old 09-05-2019, 06:09 AM   #4
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I ran 4.56 with 5spd and 35's on my TJ, it was okay on the street, 4.88 would have been a better option for passing or on ramp merge etc.. Really depends if you are planning to stick with the 35's.. though for the cost I would just keep the 5.13's.
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Old 09-05-2019, 10:08 AM   #5
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Keep the 5.13s.



Depending on the transmission 5.38s may even be more ideal.
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Old 09-05-2019, 01:14 PM   #6
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With the 6 speed, the ideal ratio is 4.88. 3k rpm at 75mph is a nice place to be. 5.13 isn't that far away. I say leave it alone.

NSG370/34"/4.56=2839rpm @ 75rpm
NSG370/34"/4.88=3038rpm @ 75rpm
NSG370/34"/5.13=3194rpm @ 75rpm
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Old 09-05-2019, 01:43 PM   #7
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IMO, its not worth the cost to drop from 5.13 to 4.88. It might or might not be worth it to drop from 5.13 to 4.56 depending upon your economic situation.

I would definitely not recommend 4.27 gears for that transmission with 35" tires.

@jjvw generally likes gears a step lower than my usual preference, probably because he lives at altitude and contends with mountain roads on a daily basis, which explains why he thinks 4.88 gears for your transmission and tire combination would be ideal and I would be inclined to suggest 4.56.
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Old 09-05-2019, 04:37 PM   #8
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@jjvw generally likes gears a step lower than my usual preference, probably because he lives at altitude and contends with mountain roads on a daily basis, which explains why he thinks 4.88 gears for your transmission and tire combination would be ideal and I would be inclined to suggest 4.56.
I wish my daily driving was that exciting, but it isn't. The ground is still quite flat where I exist most of the time. We do both agree that 4.27, if one can still easily find that ratio, is too steep for this wheel/trans combo.
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Old 09-05-2019, 05:26 PM   #9
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I thought you spent more time in the mountains. At least I was correct that you live at altitude.
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Old 09-05-2019, 05:44 PM   #10
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I thought you spent more time in the mountains. At least I was correct that you live at altitude.
The mountains are mostly for playtime. Denver is still in the furthest edges of the Great Plains. 🙂

As far as my gearing, mine is something of an anomaly. If your typical Coloradoan regears ever, they seem to follow the more traditional recommendations from elsewhere in the country. If there is anything to take away from my thoughts on the matter, it's that there should be nothing to fear from higher rpms.
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Old 09-09-2019, 09:43 PM   #11
Knows a couple things...

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I'd keep the 5.13 gears. Don't be afraid of the rpms, the engine is perfectly fine with them. Cars don't need rpms like your Jeep has because cars run small tires. The bigger the tire the more higher rpms are appropriate.

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