Built Dana 30 with 5.13 gears vs Built Dana 44 with 5.38 gears

I'm still confused about the gearing thing. My Jeep came from the PO with 4.88 gears on the BFG KO2 315/70R17s. Which I guess are technically 34.5"
I got 13.1 MPG with a mix of city and highway. And I can EASILY cruise down the highway at 70 MPH. It takes some time to get up to speed, but the Jeep is a big ass box being pushed down the road.
I just came home from a drive on Saturday and I'll need to fill up to check the 100% highway mileage. I'll try to report that back tomorrow.
Don't you lose some lower-end performance by gearing up as high as possible?
 
Something else to think about. The weight difference between front Dana 44 and Dana 30 is substantial, yet they share the same outer C and axle tube size. I've built numerous Jeeps with swapped in front dana 44s and if I were to do another 42RLE version on 35s I'd just run a Dana 30 with 5.13 gears, a selectable locker, and upgraded axle shafts.

Another thing to keep in mind is that you should be weight conscious when adding anything to your Jeep. Any additional weight you add impacts its overall performance. Given the stock engine and transmission, a lighter Jeep will accelerate, stop, and generally climb obstacles better than a heavier version. Bottom line, weight is something more people should think about, but they don't. Maybe it's a bad analogy, but the same principle applies to the human body.
 
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Jerry Bransford said:
When regearing from, say, a 3.73 to a 5.13 you are going to a deeper aka lower ratio. That gives better acceleration via higher engine rpms and can actually result in better mpg when you are regearing to a ratio that puts the engine into its 'power band' so it operates more efficiently.

When I regeared my axles from 4.88 for my 35's and 42RLE to 5.38, I went from sub-12 mpg to over 14 mpg on the highway due to the engine operating more efficiently at the slightly higher rpms. I.E. lower rpms don't necessarily give better mpg, it depends on several variables. :)
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Ohhh wow thank you! do you know what specific rpms the ideal power band is on the highway? And with 5.38 are you able to use OD to keep you in that range?
 
Irun said:
Something else to think about. The weight difference between front Dana 44 and Dana 30 is substantial, yet they share the same outer C and axle tube size. I've built numerous Jeeps with swapped in front dana 44s and if I were to do another 42RLE version on 35s I'd just run a Dana 30 with 5.13 gears, a selectable locker, and upgraded axle shafts.

Another thing to keep in mind is that you should be weight conscious when adding anything to your Jeep. Any additional weight you add impacts its overall performance. Given the stock engine and transmission, a lighter Jeep will accelerate, stop, and generally climb obstacles better than a heavier version. Bottom line, weight is something more people should think about, but they don't. Maybe it's a bad analogy, but the same principle applies to the human body.
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Good to know man thanks! Went with metalcloak highlines and opted for the aluminum, going to try to keep it as light as possible!
 
Nightmare9 said:
I'm still confused about the gearing thing. My Jeep came from the PO with 4.88 gears on the BFG KO2 315/70R17s. Which I guess are technically 34.5"
I got 13.1 MPG with a mix of city and highway. And I can EASILY cruise down the highway at 70 MPH. It takes some time to get up to speed, but the Jeep is a big ass box being pushed down the road.
I just came home from a drive on Saturday and I'll need to fill up to check the 100% highway mileage. I'll try to report that back tomorrow.
Don't you lose some lower-end performance by gearing up as high as possible?
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Thanks for writing in man 👍
 
In rock crawling its just that,very slow wheel speed. For mud you want wheel speed to keep the tire tread clean so the tires keep digging. You should build your rig for the terrain you intend to use it in most of the time.
 
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Tioga river Rat said:
In rock crawling its just that,very slow wheel speed. For mud you want wheel speed to keep the tire tread clean so the tires keep digging. You should build your rig for the terrain you intend to use it in most of the time.
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Unless a rig is trailered and not driven to the trail, it should be geared for the highway if it's a daily driver, not for its type of offroad use. When in 4Lo there's not a big difference between, for example, 4.88 and 5.38.

If you had the 42RLE automatic transmission as the OP, Chris, i, and many others here do instead of your NSG370 manual transmission you would understand why we are recommending 5.13 or 5.38 for his 35's and 42RLE automatic transmission.
 
In my 01 tj that I drive now I run 3;73 with 35's. I don't live in the mountains its flat where I live, I just drove 2.5hrs to the N.C line a few weeks ago and ran in 5th gear up and down small hills without any problem. I ran 73-75 the whole way turning around 2300rpms, in mud I run 2nd gear lo range and have good wheel speed. But you have to take into account YOUR terrain flat,mountains etc while putting your rig together.
 
Tioga river Rat said:
In my 01 tj that I drive now I run 3;73 with 35's. I don't live in the mountains its flat where I live, I just drove 2.5hrs to the N.C line a few weeks ago and ran in 5th gear up and down small hills without any problem. I ran 73-75 the whole way turning around 2300rpms, in mud I run 2nd gear lo range and have good wheel speed. But you have to take into account YOUR terrain flat,mountains etc while putting your rig together.
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Okay okay thank you, and are you auto as well or manual?
 
Tioga river Rat said:
In my 01 tj that I drive now I run 3;73 with 35's. I don't live in the mountains its flat where I live, I just drove 2.5hrs to the N.C line a few weeks ago and ran in 5th gear up and down small hills without any problem. I ran 73-75 the whole way turning around 2300rpms, in mud I run 2nd gear lo range and have good wheel speed. But you have to take into account YOUR terrain flat,mountains etc while putting your rig together.
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The correct ratio for your TJ with 35's with its NSG370 6-speed manual transmission will be way different than the same rig but with the 42RLE automatic transmission. A ratio that works well for a manual transmission like yours will NOT work well for the OP's 42RLE automatic transmission. Apples and oranges.
 
Jerry Bransford said:
Unless a rig is trailered and not driven to the trail, it should be geared for the highway if it's a daily driver, not for its type of offroad use. When in 4Lo there's not a big difference between,for example, 4.88 and 5.38.

If you had the 42RLE automatic transmission as the OP, Chris, i, and many others here do instead of your NSG370 manual transmission you would understand why we are recommending 5.13 or 5.38 for his 35's and 42RLE automatic transmission.
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I think you mean a nv3550, my old tj was a 6 speed. And to the OP I have a 5 speed manual.
 
If he drives it on the interstate at 70mph in 3rd gear he'll be at 3500rpm's with the od about 3000rpm's right? That's more than I would like to turn for a couple of hours on the highway. But if he lives in the mountains I guess that would be fine.
 
Tioga river Rat said:
If he drives it on the interstate at 70mph in 3rd gear he'll be at 3500rpm's with the od about 3000rpm's right? That's more than I would like to turn for a couple of hours on the highway. But if he lives in the mountains I guess that would be fine.
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Many of the manual owners prefer to target 3000 RPM at 75 mph in the final OD gear. There is nothing wrong with running that RPM; it gives good torque while still having good fuel economy.

For a 5 speed, that generally results in 5.13 for 35s, and 4.88 for 35s on a 6 speed.

For a 3 speed auto, that would be the equivalent of 4.10, as the 3 speed has no OD.

For a 4 speed auto, that is the equivalent of 5.89 gears, which can only be installed in a TJ Rubicon with aftermarket carriers.


I currently have a 6 speed, 4.10 gears, and 35s. I plan to regear to 4.88. In the meantime, I almost never use 6th gear, and use 5th on the highway. 5th gear and 4.10s has the exact same final drive ratio as 6th gear and 4.88s, so I'm running the RPMs I expect to get after the regear. I have had zero issues running 3000+ RPM for 12+ hours a day.

A stock TJ Rubicon with a 6 speed does almost 3000 RPM at freeway speeds from the factory. There is nothing bad about running that RPM; otherwise Jeeps wouldn't have come from the factory like that.
 
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Tioga river Rat said:
I think you mean a nv3550, my old tj was a 6 speed. And to the OP I have a 5 speed manual.
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Your Profile still shows NSG370.

Tioga river Rat said:
If he drives it on the interstate at 70mph in 3rd gear he'll be at 3500rpm's with the od about 3000rpm's right? That's more than I would like to turn for a couple of hours on the highway. But if he lives in the mountains I guess that would be fine.
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Why would he drive his 4-speed automatic in 3rd gear? He'll be at around 2600 rpms on the highway when in 4th gear. The OP's 42RLE is a 4-speed automatic, it was the older 32RH that was a 3-speed automatic.
 
That's a old pic in my profile I no longer have that tj. 2600 isn't bad on the freeway but I still would not want my jeep turning 3k for hours on end. Isn't his trans ratio 1st 2;84;1 2nd 1;57;1 3rd 1;1 4th .69;1?

OP- What tires and gears are you currently running?
 
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