Is anyone running 3.73 gears with 31s and the 42RLE?

TexasTJ2004 said:
IMO,
NSG370/29.5"/3.73 = 2498rpm @ 70mph (over 400rpm higher than the 42rle)
Represents the best "stock" (ratio wise) to which I am trying to return, not the
42rle / 29.5" /3.73 = 2052rpm @ 70mph
Which is represents garbage RPM even in the stock form.
I have driven TJ 4.0 with 6 speed a lot in past, and it was best combination of highway RPM, power etc.

With our tire combo, 4.88 will provide more power, but more fuel consumption, which is much better for hilly terrain, and 4.56 will be a better choice for flat as a tile place.
So my conclusion is that for gear ratio, one needs to look at engine, transmission, tires (real tire size, not the advertised ones), tire pressure expected on highway (size changes with pressure), and the terrain for which one plans to optimize the gearing.
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Don’t assume that 4.88 automatically means worse MPG than 4.56. Many of us here, myself included, have had better mpg from the numerically higher ratio.

I would not want to regear to a ratio that puts me at 2500 at 70. I want to be more around 2800 at 70 if possible and 3000 at 75.
 
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Assu
machoheadgames said:
Don’t assume that 4.88 automatically means worse MPG than 4.56. Many of us here, myself included, have had better mpg from the numerically higher ratio.

I would not want to regear to a ratio that puts me at 2500 at 70. I want to be more around 2800 at 70 if possible and 3000 at 75.
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Assuming that you have 42RLE, 4.0 and even stock Sport tires (29.5 properly inflated and all), in order to get to 2800 RPM at 70MPH, you will need 5.13 gears at least (real calculation shows around 5.22, but that gear ratio does not exist).
If you want such a high RPM, you might as well wire the OverDrive off by default, and stay with 3.73 gears - they together with overdrive ratio of 0.69 will put you around 3000RPM at 70. :)
 
TexasTJ2004 said:
I never assumed that 5.13 gears from Revo (i think that they make the 5.13 for Dana 30), will be too weak for open diff. However, my goal is run autolocker (Grizzly in my case), which stresses the hell out of ring and pinion. Do you believe that 5.13/Dana30 will be OK even with autolocker like Detroit/Grizzly?
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Absolutely no problem whatsoever.
 
TexasTJ2004 said:
Assu

Assuming that you have 42RLE, 4.0 and even stock Sport tires (29.5 properly inflated and all), in order to get to 2800 RPM at 70MPH, you will need 5.13 gears at least (real calculation shows around 5.22, but that gear ratio does not exist).
If you want such a high RPM, you might as well wire the OverDrive off by default, and stay with 3.73 gears - they together with overdrive ratio of 0.69 will put you around 3000RPM at 70. :)
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I don’t have the 42, just saying that 2800 @ 70 is a really solid place to shoot for. I have told myself many times that if I was a 42 owner, I would probably honestly gear it like the 32 and drive it like a 3 speed permanently. Especially if it were a rubi and I wanted 33’s, it would be geared perfectly stock. Lessens potential unwanted vibrations and solves the 0.69 OD BS. Crank it up, shut off OD (or wire it with the relay trick to kill it by default at crank up), and go.
 
Noob here. Reading this thread has got me thinking...I noticed after a week in the new Jeep that my OD kicks in way to early and leaves the vehicle feeling neutered. It has new 30" tires on it (same size from factory) and according to the equipment sheet, mine came with the 3.73 Rear Axle Ratio. Have a few questions:

1. Is it "normal" to turn OD off on a regular basis? I don't know why but it seems cruel to have the engine operating at higher RPM but I suppose it's easier on the trans (I have the 42RLE).

2. Why does my OD kick in so soon?

3. I plan on getting 32" tires, this thread suggests 4.88 based on my wheel size and trans. What does this mean in terms of driving experience? Can someone explain how it will "feel" or operate compared to stock? I spend 99% of my driving on back roads.
 
Gilly11277 said:
Noob here. Reading this thread has got me thinking...I noticed after a week in the new Jeep that my OD kicks in way to early and leaves the vehicle feeling neutered. It has new 30" tires on it (same size from factory) and according to the equipment sheet, mine came with the 3.73 Rear Axle Ratio. Have a few questions:

1. Is it "normal" to turn OD off on a regular basis? I don't know why but it seems cruel to have the engine operating at higher RPM but I suppose it's easier on the trans (I have the 42RLE).

2. Why does my OD kick in so soon?

3. I plan on getting 32" tires, this thread suggests 4.88 based on my wheel size and trans. What does this mean in terms of driving experience? Can someone explain how it will "feel" or operate compared to stock? I spend 99% of my driving on back roads.
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1. Absolutely normal if you want any bit of performance. It isn't cruel at all, engines have a range they operate decently in and ranges where they operate poorly in. OD at 40 mph and 1100 rpm would be one of the places where it operates poorly.

2. Poor programming and Chrysler pretending to try and get good fuel economy and lower emissions to please the EPA.

3. You can really go 4.88, 5.13 or even 5.38 if you have a Rubi. The overdrive is so steep that really any of those ratios will work. What you will feel is better acceleration, better ability to hold speed in 4th, and overall just better drivability. The trans will still shift into 4th too early, lugging the engine and so you'll still probably want to turn OD off a lot of the time if you are not going highway speed. The neutered feeling will be helped quite a bit by the regear, as you are bringing the engine to operate in a range it works decently in. The factory really did not gear them right to begin with, because like I said before, it was a half ass attempt at fuel economy and lowering emissions. It did lower emissions, but if anything it hurt MPG because the 4.0 is not efficient at all with the 4th gear in the 42RLE. they use a formula to calculate the advertised mpg ratings, and the lower rpm helps the theoretical formula promise a good mpg number. However, real world usage does not work the same way.
 
machoheadgames said:
1. Absolutely normal if you want any bit of performance. It isn't cruel at all, engines have a range they operate decently in and ranges where they operate poorly in. OD at 40 mph and 1100 rpm would be one of the places where it operates poorly.

2. Poor programming and Chrysler pretending to try and get good fuel economy and lower emissions to please the EPA.

3. You can really go 4.88, 5.13 or even 5.38 if you have a Rubi. The overdrive is so steep that really any of those ratios will work. What you will feel is better acceleration, better ability to hold speed in 4th, and overall just better drivability. The trans will still shift into 4th too early, lugging the engine and so you'll still probably want to turn OD off a lot of the time if you are not going highway speed. The neutered feeling will be helped quite a bit by the regear, as you are bringing the engine to operate in a range it works decently in. The factory really did not gear them right to begin with, because like I said before, it was a half ass attempt at fuel economy and lowering emissions. It did lower emissions, but if anything it hurt MPG because the 4.0 is not efficient at all with the 4th gear in the 42RLE. they use a formula to calculate the advertised mpg ratings, and the lower rpm helps the theoretical formula promise a good mpg number. However, real world usage does not work the same way.
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Good info. #2 was probably a given. Seems like most companies are doing "on paper" changes to satisfy the EPA. I come from a long history of Honda/Toyota so perhaps my mindset is off a bit with certain things. Idk why but in the back of my mind I always think American engines can't run with their Jap counterparts so it just seems like a bad idea to run the 4.0L harder. I know i know, these engines are pretty tough, I'll get there eventually...
 
machoheadgames said:
2. Poor programming and Chrysler pretending to try and get good fuel economy and lower emissions to please the EPA.
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The Jeep is tested at an EPA facility and the mileage and emissions numbers are real. The inline six was discontinued in 2006 because pretend doesn't count at the EPA. It does count here when talking about economy so feel free to pretend away.
 
pagrey said:
The Jeep is tested at an EPA facility and the mileage and emissions numbers are real. The inline six was discontinued in 2006 because pretend doesn't count at the EPA. It does count here when talking about economy so feel free to pretend away.
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If you put on your glasses and read, you'll see that I never said the emissions numbers weren't real.

As for the mpg portion, surely you realize that not every vehicle is actually tested by the EPA? Many of them are going off of manufacturer's word. There is a reason why virtually none of the "estimates" are accurate either. Based on your logic, the TJ would get better gas mileage with stock gears than otherwise in pretty much any scenario. Real world proves that wrong majority of the time.
 
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