gears & gas mileage
Thread Starter
JK Newbie
Joined: Jan 2010
Posts: 12
Likes: 0
From: beachcity, tx
gears & gas mileage
OK, I'm talking about a 4 door auto with 35s
What I understand is most of you think an auto should run 5.13s with 35s
and the 6 speeds with 35s should run 4.88
but at what cost, to fuel mileage , ( I run from Houston to San Antonio a lot )
I read that there is a tire size RPM chart on here somewhere but I can't find it ?
I'm thinking 4.88s might be better in my case, what do you think?
What I understand is most of you think an auto should run 5.13s with 35s
and the 6 speeds with 35s should run 4.88
but at what cost, to fuel mileage , ( I run from Houston to San Antonio a lot )
I read that there is a tire size RPM chart on here somewhere but I can't find it ?
I'm thinking 4.88s might be better in my case, what do you think?
JK Junkie
Joined: Jul 2009
Posts: 2,343
Likes: 1
From: The San Andreas Fault
The gear chart is in the FAQ of this section.
Unless you change your driving habits most of your reduction in gas mileage is going to come from the increase in mass of the larger wheels.
I increased my cruising RPM by ~400-500 RPM when I added gears and tires and my MPG went down ~2.5 MPG.
However part of that is because I also reprogrammed my PCM with a Flashpaq which made the engine/tranny more responsive. So now I step on the skinny more often because I know it will respond, where as before it was an exercise in futility.
Unless you change your driving habits most of your reduction in gas mileage is going to come from the increase in mass of the larger wheels.
I increased my cruising RPM by ~400-500 RPM when I added gears and tires and my MPG went down ~2.5 MPG.
However part of that is because I also reprogrammed my PCM with a Flashpaq which made the engine/tranny more responsive. So now I step on the skinny more often because I know it will respond, where as before it was an exercise in futility.
JK Junkie
Joined: Jul 2008
Posts: 3,017
Likes: 0
From: Lakewood, OH
OK, I'm talking about a 4 door auto with 35s
What I understand is most of you think an auto should run 5.13s with 35s
and the 6 speeds with 35s should run 4.88
but at what cost, to fuel mileage , ( I run from Houston to San Antonio a lot )
I read that there is a tire size RPM chart on here somewhere but I can't find it ?
I'm thinking 4.88s might be better in my case, what do you think?
What I understand is most of you think an auto should run 5.13s with 35s
and the 6 speeds with 35s should run 4.88
but at what cost, to fuel mileage , ( I run from Houston to San Antonio a lot )
I read that there is a tire size RPM chart on here somewhere but I can't find it ?
I'm thinking 4.88s might be better in my case, what do you think?
https://www.jk-forum.com/forums/show...76&postcount=4
As for mileage, kick downs will negatively effect your mileage more than a couple hundred rpms. 4.88s, an auto and a heavier unlimited is also a dead end as far as moving further up in tire size.
Being in Texas, and relatively flat you might do OK with the 4.88s as far as economy goes, but even so over the life of your Jeep there is no way it would pay for doing it twice.
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Thread Starter
JK Newbie
Joined: Jan 2010
Posts: 12
Likes: 0
From: beachcity, tx
Here's the gear chart,
https://www.jk-forum.com/forums/show...76&postcount=4
As for mileage, kick downs will negatively effect your mileage more than a couple hundred rpms. 4.88s, an auto and a heavier unlimited is also a dead end as far as moving further up in tire size.
Being in Texas, and relatively flat you might do OK with the 4.88s as far as economy goes, but even so over the life of your Jeep there is no way it would pay for doing it twice.
https://www.jk-forum.com/forums/show...76&postcount=4
As for mileage, kick downs will negatively effect your mileage more than a couple hundred rpms. 4.88s, an auto and a heavier unlimited is also a dead end as far as moving further up in tire size.
Being in Texas, and relatively flat you might do OK with the 4.88s as far as economy goes, but even so over the life of your Jeep there is no way it would pay for doing it twice.
losing 2.5 mph doesn't sound good
JK Freak
Joined: Dec 2009
Posts: 882
Likes: 1
From: Keene, New Hampshire, United States
i would think that if you increase the outside diameter and reduce your gearing to compensate, your gas mileage would not be affected as badly as some are saying. it does take slightly more power to set a heavier wheel/tire combo in motion but the gear reduction should actually save gas if the engine doesn't have to work so hard to turn the larger meat. just my 2 cents :P