35's and 5.13 or 4.88 gears?
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JK Newbie
Joined: Mar 2013
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From: Fort Worth, TX
35's and 5.13 or 4.88 gears?
I have a 2009 JK Unlimited X (4 speed auto w/OD) with 3.73 gearing. Will be adding a 2.5 TF coil lift to run 35's. In terms of MPG and power would it be better to re-gear to 4.88 or 5.13? This is also my daily driver. Any feedback is greatly appreciated!
JK Enthusiast
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From: Orange County
JK Jedi Master
Joined: Jan 2008
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From: Austin <--> Colorado Springs
Your best bet would be to just get the new 35's and drive it first. Turn the OD Off, and you'll get a decent feel for the freeway gearing you would have with 5.38's. (Divide rpm by .69 to get od off rpm)
As an example, using numbers from the rpm chart in the modified faq's and 34" as actual tire height for the 35's:
3.73 / 34" = 1781 rpm @ 70
O/D off = 2581 rpm @ 70
5.13 / 34 = 2450 rpm @ 70
5.38 / 34 = 2569 rpm @ 70
It won't be the same around town, but od off with 3.73 will be close to the feel of 35's and 5.38's, and just over a 100 rpm higher than you would have with 5.13's. (not taking bigger tires / lift into account, of course).
As an example, using numbers from the rpm chart in the modified faq's and 34" as actual tire height for the 35's:
3.73 / 34" = 1781 rpm @ 70
O/D off = 2581 rpm @ 70
5.13 / 34 = 2450 rpm @ 70
5.38 / 34 = 2569 rpm @ 70
It won't be the same around town, but od off with 3.73 will be close to the feel of 35's and 5.38's, and just over a 100 rpm higher than you would have with 5.13's. (not taking bigger tires / lift into account, of course).
JK Enthusiast
Joined: Aug 2010
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From: Park City, Utah
Chart shows you the optimum gear ratios based on your tire size and transmission type.
So, you'd want to be in a 5.13 or 5.38 with 35" tires ... choice would depend somewhat on the type of terrain you normally drive.
I'm in the Western Rockies with some fairly steep climbs between 5,000 to 7,000 ft on a daily commute -- for my area, I'd choose the 5.38. Texas is fairly flat, low altitude, so you might get by with a 5.13.
Think you'll find a 4.88 is a bit sluggish regardless of where you're at.
Alll In My Humble Opinion of course.
So, you'd want to be in a 5.13 or 5.38 with 35" tires ... choice would depend somewhat on the type of terrain you normally drive.
I'm in the Western Rockies with some fairly steep climbs between 5,000 to 7,000 ft on a daily commute -- for my area, I'd choose the 5.38. Texas is fairly flat, low altitude, so you might get by with a 5.13.
Think you'll find a 4.88 is a bit sluggish regardless of where you're at.
Alll In My Humble Opinion of course.
Last edited by nickcoleman; Mar 31, 2013 at 06:46 AM.
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