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post #1 of 13 Old 02-24-2009, 06:06 PM Thread Starter
 
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Gears which to use for real life

I know this has been asked before somewhere. I have a rubi. 4.10's in the pumpkins. I am running 35's. Am looking for real world advice on 4.88's or 5.13's. My rig is a daily driver. I am sucking 14mgs's right now, would be nice to get some of the fuel economy back.
thanks in advance
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post #2 of 13 Old 02-24-2009, 06:41 PM
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Originally Posted by Red Rock Local View Post
I know this has been asked before somewhere. I have a rubi. 4.10's in the pumpkins. I am running 35's. Am looking for real world advice on 4.88's or 5.13's. My rig is a daily driver. I am sucking 14mgs's right now, would be nice to get some of the fuel economy back.
thanks in advance
If you plan on sticking with the 35's I would go with 4.88's


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post #3 of 13 Old 02-24-2009, 08:36 PM
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Manual tranny or automagic? The auto has a much taller overdrive, so I'd go 5.13 or 5.38. (yes, even with 35's) If it's a manual, then you'll need to try to predict if you'll stick with 35's forever or move to larger tires in the future, that will make the difference in my mind between 5.13 or 4.88's.


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post #4 of 13 Old 02-24-2009, 10:11 PM
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I agree with Tera, i have 5.13's with 35's and a slushbox and i wish i could stick 5.30's or so in there. But then again i like to be able roast my tires at will.
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post #5 of 13 Old 02-24-2009, 10:16 PM
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yup 5.13s w/ an auto here
kinda wish I had gone to 5.38s


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post #6 of 13 Old 02-24-2009, 10:43 PM
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With my stock setup of 3.73s and 32" tires I get around 21 mpg. Seems with 33" tires you would want 4.10s and with 35"s you would want 4.56 to keep around the same mileage. Does that sound about right? If you went higher then your mileage would go back down. Correct me if I'm wrong here. 4.88 seems a little much for a DD.
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post #7 of 13 Old 02-24-2009, 11:18 PM
 
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I'am running 5.13's cause I thought that was the be all end all solution to pushing 35's and keeping 15mpg. Now I find out people wish they went higher. Never feel like I can win. On the plus side I love my JK performance with what I got and still a happy man. 5.13's are great for real world daily driving use.
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post #8 of 13 Old 02-25-2009, 04:03 AM
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Originally Posted by woffles View Post
With my stock setup of 3.73s and 32" tires I get around 21 mpg. Seems with 33" tires you would want 4.10s and with 35"s you would want 4.56 to keep around the same mileage. Does that sound about right? If you went higher then your mileage would go back down. Correct me if I'm wrong here. 4.88 seems a little much for a DD.
Exactly, This guy wants to keep close to the stock final gear ratio and I believe the perfect ratio is a 4.63 with 35's.


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post #9 of 13 Old 02-25-2009, 06:23 AM
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Does anybody here really drive these things with different gears or are you too busy with your calculators to get behind the wheel? Here's the real skinny on gears for an A/T:
This used to be an '07 Sahara Unlimited with an AT. Stuff that may effect the numbers include full RH skids, full doors, hardtop, Shrockworks sliders, Nates 4x4 full width bumper, 9500ti winch, Currie (massive) control arms F&R, diff armor, chromoly axles F&R, wheel spacers, Tuffy everything, RH rear bumper/tire carrier, j-can carriers, at anytime about 50 lbs (minimum) recovery gear and me at about 200 lbs.
It's running a D44 in the front, an Atlas 4sp T/C with about 850 miles on it and the 5.13's have about 350 mi on them. Almost its entire life has been spent at 6,000 feet or better.

I reset the gear ratio and tire size (measured at 32" BFG 285/70/17 KM2's siped and running at about 32 PSI on stock Moab {Rubi} wheels) with my new AEV Procal.. If you're regearing, buy one of these now!

Here are the numbers taken from the flatest part of the highway.
45 mph 1500 rpm
50 1800
55 a hair under the 2000 mark
60 2100
65 2300
That was as fast as I dare go. Oh yeah the MPG thing never dropped below 18.7 for whatever that's worth.
Now for the best part, I PASSED TWO TRUCKS GOING UPHILL! It's been a long time since I've been able to do that.
It's also the first time in who knows when that I didn't have to turn the overdrive off on that road.

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post #10 of 13 Old 02-25-2009, 06:38 AM
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i have 5.13's with 35's on my manual. as my daily driver, right now, i wish i had 4.88's. right now, 5.13's suck on the highway because i run about 3000rpm's at 70mph.

someday when i go to 37's or 38's, i'll be glad i have 5.13's.

i wanted to go with 4.88's for the present, but decided to go with 5.13's, because i'll ultimately want them down the road.

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post #11 of 13 Old 02-25-2009, 08:16 AM
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mcnaught6 and I are on the same page. I love having 5.13's for any speed under 65. In 6th gear, I can go up a nice hill at 50 mph and not downshift. My MPG's are about 2-3 mpg better now with the 5.13's vs 4.10's and 35's (manual tranny).

37's aren't too far away though and that will be sweet with 5.13s.

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post #12 of 13 Old 02-25-2009, 08:38 AM
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Quote:
Originally Posted by woffles View Post
With my stock setup of 3.73s and 32" tires I get around 21 mpg. Seems with 33" tires you would want 4.10s and with 35"s you would want 4.56 to keep around the same mileage. Does that sound about right? If you went higher then your mileage would go back down. Correct me if I'm wrong here. 4.88 seems a little much for a DD.
In theory and on paper you would be correct however you also need to take into account the rolling resistance of a larger, heavier tire. Unsprung weight is the enemy of fuel economy. If you are interested in squeezing the best mileage out of your JK go with the 5.13's. as you add more farkles to your jeep its weight will increase causing more rolling resistance ergo using more fuel.
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post #13 of 13 Old 02-25-2009, 04:44 PM
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Quote:
Originally Posted by Mikey's Rubi View Post
mcnaught6 and I are on the same page. I love having 5.13's for any speed under 65. In 6th gear, I can go up a nice hill at 50 mph and not downshift. My MPG's are about 2-3 mpg better now with the 5.13's vs 4.10's and 35's (manual tranny).

37's aren't too far away though and that will be sweet with 5.13s.
He did say he had an auto. The overdrive takes care of that over revving issue. I don't know personally, but I've heard many recommend 4.88's even for 37's for JK's with manuals.

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