4.88 or 5.13 on a Automatic
JK Super Freak
Joined: Mar 2010
Posts: 1,399
Likes: 1
From: Next To You
I'm not running a programer even though I really would like to have one. I run my tires at 38psi which has to do with what kind of fuel mileage I get also.
What is the terrain like where you live?
What is the terrain like where you live?
Last edited by jeepoholic; Jan 23, 2011 at 04:40 PM.
JK Enthusiast
Joined: Sep 2010
Posts: 135
Likes: 0
From: Denver, CO
I'll just tell you what I've experienced over the last few years. I've owned several Jeeps with this same auto transmission, and have used them with everything from 4.10 gears and 37" tires, to 4.88 gears with both 35" and 37" tires, to 5.38 gears with 35" tires. So I've pretty much tried them all.
I think 4.88 gears are the worst possible combination you can choose for highway use with this auto transmission. At one extreme, with the stock 4.10 gears, it will be more sluggish around town, but on the highway you just drive with the overdrive off, and third gear feels pretty decent. It is still geared so high that third gear is not over revving the engine, even driving down the interstate. At the other extreme, with 5.38 gears, it is geared low enough that it stays in overdrive for level ground, and even for some minor hills. But with 4.88 gears, you're right in the middle. It isn't geared low enough to stay in overdrive as well as it should, but when it downshifts to third gear it has to rev significantly higher than with stock gears. You don't feel like driving with overdrive off with 4.88 gears, and it won't stay in overdrive either. The Jeep I owned with 4.88 gears was the worst one I've owned for driving on the highway.
This is something you shouldn't do half-assed, and 4.88 gears are just that. Gear it low enough to make a difference. I recommend 5.13s.
I think 4.88 gears are the worst possible combination you can choose for highway use with this auto transmission. At one extreme, with the stock 4.10 gears, it will be more sluggish around town, but on the highway you just drive with the overdrive off, and third gear feels pretty decent. It is still geared so high that third gear is not over revving the engine, even driving down the interstate. At the other extreme, with 5.38 gears, it is geared low enough that it stays in overdrive for level ground, and even for some minor hills. But with 4.88 gears, you're right in the middle. It isn't geared low enough to stay in overdrive as well as it should, but when it downshifts to third gear it has to rev significantly higher than with stock gears. You don't feel like driving with overdrive off with 4.88 gears, and it won't stay in overdrive either. The Jeep I owned with 4.88 gears was the worst one I've owned for driving on the highway.
This is something you shouldn't do half-assed, and 4.88 gears are just that. Gear it low enough to make a difference. I recommend 5.13s.
JK Super Freak
Joined: Mar 2010
Posts: 1,139
Likes: 0
From: The OC
OK, I just did both ...
My Jeep: 4 door, Automatic, 37"s, Superchip - 5.13's
Son's Jeep: 2 door, Automatic, 35"s, Superchip - 4.88's
This is the correct set-up for both situations. Could have gone 5.38's on the 4 door, but I intend to do some hard wheeling and wanted the extra strength.
My Jeep: 4 door, Automatic, 37"s, Superchip - 5.13's
Son's Jeep: 2 door, Automatic, 35"s, Superchip - 4.88's
This is the correct set-up for both situations. Could have gone 5.38's on the 4 door, but I intend to do some hard wheeling and wanted the extra strength.
JK Freak
Joined: Sep 2009
Posts: 894
Likes: 0
From: Kirkland, WA
Toyo stated specs on the 35x12.5x18 are 35" exactly, I'm running 35x12.5x17 that they state is 34.8"...either way I'm running 5.13's with my auto and wouldn't want it any other way. I can run 80mph on the highway up here @ 2700RPM no issues. Off-road they are the most ridiculous change over 4.10's (in a good way). I get ~1mpg better mileage because I no longer have to floor it getting on the highway or merging into traffic.