'06 Unlimited Rubicon (6 Spd) w/35-37s - Re-Gear 4.88? - JeepForum.com
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Unread 11-27-2014, 12:14 AM   #1
Altonymous
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'06 Unlimited Rubicon (6 Spd) w/35-37s - Re-Gear 4.88?

Title pretty much says it all.

I currently have 35s on my jeep and about to re-gear to 4.88. Would 4.88 be enough for 37s if I ever decide to go 37s?

Thanks in advance for your advice!

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Unread 11-27-2014, 12:26 AM   #2
geroux
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Can't speak of the 6 speed but I have a 5 speed with 4.88 and 35's and that's about as high (numerically low) as I would go. I almost wish I did 5:13's. If you're considering 37" tires I'd go 5.13.
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Unread 11-27-2014, 01:47 AM   #3
DezertTJ
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4.88s should be fine for both. The 6 spd with 4.10s on heavy 35s is good, I can only imagine 4.88s and 37s being great
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Unread 11-27-2014, 03:59 AM   #4
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Originally Posted by DezertTJ View Post
4.88s should be fine for both. The 6 spd with 4.10s on heavy 35s is good, I can only imagine 4.88s and 37s being great
Nah, 5.13s. 4.88 is great for 35s
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Unread 11-27-2014, 08:21 AM   #5
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When reading the 3 previous responses, notice that both of the people who say 5:13s have the 5 speed. The 1 guy who suggests 4:88s has the 6 speed. 6th is a lower gear in our transmission than 5th is in theirs so in theory, we wouldn't need to gear as low as they do.

Also, I would think that this decision would be heavily dependent on your location and how much extra weight you have added. In NC, with a reasonably stock weight Jeep, I'd say 4:88 for 37s. I just wheeled with someone who has that set up and he is very happy.
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Unread 11-27-2014, 10:26 PM   #6
joe_jeep
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Use the grimmjeeper calculator. Aim for 2600 to 2800 at 70mph. Jmho.
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Unread 11-27-2014, 11:16 PM   #7
NumbSkull
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I'm running 35s with a 6 speed and just finished regearing to 4.88, and I'm pretty happy with it... the 4.88 is a little low, and first gear isn't worth much in mall-crawler mode, but I built it for the rocks, and have been very happy with it on the trails. I've never ran 37s, but I think it would be a good match for that sized tire as well.. Might even be a better match than it is for the 35s, since it would likely give some more function back to first gear when on road.
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Unread 11-27-2014, 11:22 PM   #8
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Quote:
Originally Posted by srfnfly227 View Post
When reading the 3 previous responses, notice that both of the people who say 5:13s have the 5 speed.
Which is why I first disclosed the fact that I had a 5-speed. My suggestion is based on the 1:1 4th gear performance, or in his case 5th gear. Just an opinion. I can say that I wish I had done 5:13 with my 35's so I can't imagine anything less with 37's with any speed trans.
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Unread 11-27-2014, 11:53 PM   #9
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So I was just screwing around with the grimjeeper calculator and came to the following conclusions:

With the 6 speed and 35" tires at 80mph your RPMs are as follows

4.88s = 3148

5.13s = 3309

Difference of 161 rpm

Crawl ratio:

4.88s = 87

5.13 = 91.5

With 6 speed, 37s at 80 mph:

4.88s = 2978

5.13s = 3131

Difference of 153 rpm.

For reference a factory 6 speed rubicon is turning 3038 rpms at 80 ( 6 speed, 245 mtrs, 4.10s)

I don't know about you guys but I was given the opportunity to drive an 06 6 speed tj rubi with less than 4k miles on it through the mountains which included 8 hours of interstate driving. I still thought the thing was underpowered especially at highway speeds.

If I was in your shoes I would absolutely spring for the 5.13s you have to remember the additional lift and rolling resistance that those bigger meats promise you will definitely slow your jeep down, it makes more than enough sense to get the slightly better than stock gearing advantage to help propel you along.
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Unread 11-28-2014, 12:04 AM   #10
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I have thought about this same situation.... and played on grimmjeeper numerous times.

I am currently on 35's with stock 4.10's with a 6 speed.
If I switch to 37's I will be going to 5.13's.


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Unread 11-28-2014, 12:29 AM   #11
DezertTJ
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While 5.13s would be great for power, the 4.88s would be more ideal for highway. I thought the 6 spd ran too high of an rpm at highway speeds, but pulls hard enough. It really varies by who the driver is though. I'm used to under geared jeeps and the 42re. So either 4.88 or 5.13 will work great. You decide
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Unread 11-28-2014, 12:38 AM   #12
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Quote:
Originally Posted by JeepnBlake View Post

For reference a factory 6 speed rubicon is turning 3038 rpms at 80 ( 6 speed, 245 mtrs, 4.10s)

I don't know about you guys but I was given the opportunity to drive an 06 6 speed tj rubi with less than 4k miles on it through the mountains which included 8 hours of interstate driving. I still thought the thing was underpowered especially at highway speeds.
Why use 80 mph as an example? I live in the mountains at 10,000 feet. I am not driving 80 mph anywhere unless I head east out past DIA on I-70. Even then, why bother? Gas mileage really tapers off after 65-70...

Unless I get on I-70, I am rarely going more than 65. Most often I am going 30-55.

Engines lose power at altitude due to less dense air. It would be for this reason that I would go slightly deeper than just right with gearing.



As for the OP- They list Cary, NC as their location which google shows to be @ 480 feet...
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Unread 11-28-2014, 01:09 AM   #13
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4.88 would be great for 35's and probably be good for 37's as well. I would also think 5.13 would be too low for the 35's.

I have 4.56 and I'm happy with it (06 LJ 6 speed on 35's). I bought it like this though. Would probably have gone with 4.88 if I had the re-gear done myself.
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Unread 11-28-2014, 01:11 AM   #14
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Originally Posted by suicideking View Post
4.88 would be great for 35's and probably be good for 37's as well. Question I have regarding 5.13 (or even 4.88) is if you have the stock axles, can you even get 5.13 in the D30 front? Rear is a D44 so should be good there. I would also think 5.13 would be too low for the 35's. If going with 37's, might want to replace the D30 first.

I have 4.56 and I'm happy with it (06 LJ 6 speed on 35's). I bought it like this though. Would probably have gone with 4.88 if I had the re-gear done myself.
The OP lists Rubi 44's...
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Unread 11-28-2014, 01:13 AM   #15
suicideking
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Originally Posted by irnmadn88 View Post
The OP lists Rubi 44's...
I fixed my post before you finished your post. Knew that would happen lol.
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