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Unread 01-10-2010, 09:08 AM   #1
Kenny
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4.88 or 5.13? advice please

I have an 06 LJ rubicon with 33 inch tires and the auto with a .69 overdrive. I live and drive in southern colorado so its a constant fight with 8% grades at least. Right now I still have the stock 4.10 gears and on just about any " hill " around here its dropping into second gear just to maintain 60 65 mph. Takes all the fun outta driving when you know its just a dog to drive. I am going to put gears in the jeep just confused about what to use. The auto in my rubi makes it seem like such a lazy jeep its killing the joy of driving a jeep.

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Unread 01-10-2010, 09:13 AM   #2
cmoore
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4.88s will be the nicest of the two at highway speeds. The 5.13s would bump your rpms pretty high by 75.
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Unread 01-10-2010, 09:21 AM   #3
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4.88s for 33s. 5.13s for 35s. but 4.88s will work with 35s, its just not ideal.

the 42RLE and the 4.0L shouldn't have been mated together, so you've got to be willing to suffer with some suck.
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Unread 01-10-2010, 09:22 AM   #4
pielet97
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I have 4.88, 42RLE and love them with 35's, but you'll find on here a lot of people praise 5.13 with 35's and the 42RLE. I have driven from Cali to IN and to Moab a couple of times, so I've seen hills.

My vote would be for 4.88
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Unread 01-10-2010, 09:52 AM   #5
Kenny
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i have been playing with the gear calc and its a tight call between the two.... i dont know what to do. Been thinkin 4.88 but according to the calc at 70 it think it said i would be at around 2500 Gear Ratio Calculator
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Unread 01-10-2010, 10:52 AM   #6
Wheelin98TJ
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Go with 5.13.

2,500 RPM at crusing speed is just about perfect.
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Unread 01-10-2010, 10:56 AM   #7
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Quote:
Originally Posted by Kenny View Post
i have been playing with the gear calc and its a tight call between the two.... i dont know what to do. Been thinkin 4.88 but according to the calc at 70 it think it said i would be at around 2500 Gear Ratio Calculator
Having run 35" tires for years, I believe 2500 at 70 mph is too low of a highway rpm. To me, for that big of a tire and the added power it takes to turn coupled with the Jeep's increased wind resistance from a suspension lift, that 2700-2750 rpms is ideal at 70 mph. That's what my TJ ran for years and I wouldn't have wanted any lower rpms.
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Unread 01-10-2010, 10:58 AM   #8
Alexia
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Originally Posted by Wheelin98TJ View Post
Go with 5.13.

2,500 RPM at crusing speed is just about perfect.
Adding to this, 2,200rpm and above is generally where the engine has no issue pulling up steep hills on the highways.
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Unread 01-10-2010, 11:04 AM   #9
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Adding to this, 2,200rpm and above is generally where the engine has no issue pulling up steep hills on the highways.
You can't make a blanket statement like that. 2200 rpms might be adequate for factory size tires but no way is 2200 enough for going up hill with 35" tires.
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Unread 01-10-2010, 11:09 AM   #10
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You can't make a blanket statement like that. 2200 rpms might be adequate for factory size tires but no way is 2200 enough for going up hill with 35" tires.
I agree I have 33's and stock 3.73's for now. On the highway i leave it in 4th gear runnin 72 at 2800rpms i get better gas milage this way and plenty of power to pull hills
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Unread 01-10-2010, 11:12 AM   #11
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Originally Posted by Jerry Bransford View Post
You can't make a blanket statement like that. 2200 rpms might be adequate for factory size tires but no way is 2200 enough for going up hill with 35" tires.
X2. Next thing you know, you're at 2100, 2000, 1900...
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Unread 01-10-2010, 11:13 AM   #12
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With 5.13, RPM at 70 will be 2,600-2,700.

I was thinking RPM would be around 2,500 with 5.13 and I misunderstood you when you previously said 2,500 was the RPM for 4.88.

I might have been misleading when I previously said 2,500 RPM is just about perfect. I was not suggesting 4.88.
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Unread 01-10-2010, 11:21 AM   #13
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Originally Posted by Jerry Bransford View Post
You can't make a blanket statement like that. 2200 rpms might be adequate for factory size tires but no way is 2200 enough for going up hill with 35" tires.
Steep hills and "2,200 and above". I can pull my Jeep up normal hills at 1,800rpm with stock 30" tires in fourth gear, but it is entirely unhappy about doing that. I am stating that 2,200 is the absolute minimum.
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Unread 01-10-2010, 11:37 AM   #14
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Based on my 4+ years of experience with the 42RLE, 35's and 4.88's...

I'd recommend 5.13's for your 33's. The 42RLE loves low gearing. The difference between 4.88 and 5.13 is only 5%. So, if you're turing 2400 with 4.88's, you'd be turning ~2520 with 5.13's. If not for my D30, I'd be running 5.13's or lower, believe me...
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Unread 01-10-2010, 01:17 PM   #15
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4.88's will be fine for 33's but if you see yourself moving up to 35's eventually then go with 5.13's.

The 5.13's will still be fine with the 33's, it will just give you a little more room to grow.
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