Another re-gear thread: 2004 TJ 4.0 with 31" tires

moonlight

moonlight

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the beautiful Pacific NW
I have a 2004 TJ 4.0l and 3.73 gears with 31" tires that really struggles on mountain passes or any relatively steep hill. I live in the Cascade foothills, so i hit a pass anytime I go east. I also tow a little travel trailer of about 1000#. I want more power for towing and climbing.
She is my daily driver, and I put a lot of miles on her (230,000 on the clock) but I avoid the freeway if possible. When I can't, I don't go much over 60-65 mph.

Will regearing to 4.56 give me the power bump I want and still allow at least 60mph on the freeway? I keep going back and forth because it's an expensive job but would be worth it if my TJ gets a little more guts.

Opinions?
 
You would love the 4.56 gears with 31’s. I had that combo for awhile and it was great. Power everywhere. You can cruise backroads with not having to shift if you don’t want to. You can go 90 mph on the highway if you want to ( not recommended but fun to pass jk’s)
 
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Regearing to 4.56 would definitely increase power but at the cost of the 2700 rpms I don't know that you'd be happy with at 70 mph with 31's. I'd consider 4.10 which will give you 2425 rpms at 70 mph which is a pretty good cruising rpm for 31's. 4.10 is the same ratio the Rubicon came with for its 31" factory size tires. I'd only consider regearing to 4.10 (or 4.56) if the cost to do so is not a big deal to you. Either ratio will give you a nice bump in power and reduce the need to downshift for climbs.
 
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Jerry Bransford said:
Regearing to 4.56 would definitely increase power but at the cost of the 2700 rpms I don't know that you'd be happy with at 70 mph with 31's. I'd consider 4.10 which will give you 2425 rpms at 70 mph which is a pretty good cruising rpm for 31's. 4.10 is the same ratio the Rubicon came with for its 31" factory size tires. I'd only consider regearing to 4.10 (or 4.56) if the cost to do so is not a big deal to you. Either ratio will give you a nice bump in power and reduce the need to downshift for climbs.
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2700 rpm at 70 on 31's is as nice as it is on 35's at 2700 rpm. I had 4.10 and 31's for a while with the 5-speed, I pretty much always wished for 4.56 after I did it.
 
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machoheadgames said:
2700 rpm at 70 on 31's is as nice as it is on 35's at 2700 rpms
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I disagree, 35's require the higher rpms and I loved it when my previous TJ's engine was turning over 2700 rpms with my 35's. But that high of an rpm simply isn't needed for 31's and to me would be excessively high given the smaller size of tire that simply does not require the rpms 35's do.

The bigger the tire the more rpms it requires, the smaller the tire the lower the rpms it needs.
 
Jerry Bransford said:
I disagree, 35's require the higher rpms and I loved it when my previous TJ's engine was turning over 2700 rpms with my 35's. But that high of an rpm simply isn't needed for 31's and to me would be excessively high given the smaller size of tire that simply does not require the rpms 35's do.

The bigger the tire the more rpms it requires, the smaller the tire the lower the rpms it needs.
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I'm not new to this. As I said, I had 4.10 and 31's for a long time. I wanted more. It is not significantly more difficult to turn a 35 than a 31. Slightly, but not 2-300 worth of rpm on the highway.

There have been a few folks here who also like 4.56 on their 31's. I have not seen anyone choose that combo and NOT like it.

It would be absurd to regear from 3.73 to 4.10.
 
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machoheadgames said:
It would be absurd to regear from 3.73 to 4.10.
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That may be, solely due to its cost, but not everyone worries about that kind of cost. I simply gave her the rpms 4.10 and 4.56 would produce and made my recommendation for the 2400 rpms at 70 mph due to the small tire size. 2400 rpms at 70 mph with 31" tires is a better rpm than 2700 rpms at 70 for a 31" tire which it simply doesn't need.

If both gear changes were free 4.10 would be the better choice rpm-wise.

I'd keep it as-is at 3.73 before I'd regear to 4.56 for only 31" tires.
 
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Jerry Bransford said:
That may be, solely due to its cost, but not everyone worries about that kind of cost. I simply gave her the rpms 4.10 and 4.56 would produce and made my recommendation for the 2400 rpms at 70 mph due to the small tire size. 2400 rpms at 70 mph with 31" tires is a better rpm than 2700 rpms at 70 for a 31" tire which it simply doesn't need.

If both gear changes were free 4.10 would be the better choice rpm-wise.

I'd keep it as-is at 3.73 before I'd regear to 4.56 for only 31" tires.
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so are there other things to have my shop look at to increase power?

I would rarely go 70 (60 is more my speed when I'm on the freeway)

also, for all you guys, I know I'm going to get a little teasing when I post in these forums because I'm an old lady who doesn't do any of my own work on my TJ, but I have driven her for nearly 20 years all over the Pacific Northwest. And I have driven manual transmissions all my life.
 
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moonlight said:
so are there other things to have my shop look at to increase power?

I would rarely go 70 (60 is more my speed when I'm on the freeway)

also, for all you guys, I know I'm going to get a little teasing when I post in these forums because I'm an old lady who doesn't do any of my own work on my TJ, but I have driven her for nearly 20 years all over the Pacific Northwest. And I have driven manual transmissions all my life.
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Regearing your axles is the only realistic/cost effective way to increase your power. And if you think you're old at 62 I might just have socks older than you. :ROFLMAO:
 
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machoheadgames said:
I'm not new to this. As I said, I had 4.10 and 31's for a long time. I wanted more. It is not significantly more difficult to turn a 35 than a 31. Slightly, but not 2-300 worth of rpm on the highway.

There have been a few folks here who also like 4.56 on their 31's. I have not seen anyone choose that combo and NOT like it.

It would be absurd to regear from 3.73 to 4.10.
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Agree completely, I’m running 32’s now but 4.56 was awesome with 31’s and the 5 speed.
 
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moonlight said:
Out of curiosity, have you tried driving over a 2 lane mountain pass doing barely 40 when the speed limit is 65? It's excruciating and everyone behind you gets kind of ticked off.
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I have many, many times. Americans expect gargantuan amounts of HP in order to maintain 65/whatever uphill and down - which I find ridiculous. If its a 2 lane road, I'll pull over to let others go by when it is safe to do so AND there isn't any credible way for them to pass. OTOH, if the road is straight as an arrow for miles with no opposing traffic, if they're too stupid to pass me they can stay back there and be pissed off - not my problem. But I have yet to see a 2 lane mountain pass where the limit is anywhere near 65 - regardless, on such a road many are going slow, and I'll let the guy who can go 45 or 50 pass me when I can. Blowing up a road like that at 65 is foolhardy at best, and I'm being kind.
 
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