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

42rle / 29.5" /3.73 = 2052rpm @ 70mph

NV3550/29.5"/3.73 = 2320rpm @ 70mph (nearly 300rpm higher than the 42rle)

AX-15 / 29.5" /3.73 = 2349rpm @ 70mph (nearly 300rpm higher than the 42rle)

NSG370/29.5"/3.73 = 2498rpm @ 70mph (over 400rpm higher than the 42rle)

32rh / 29.5" / 3.73 = 2974rpm @ 70mph (nearly 900rpms higher than the 42rle)
Seeing those numbers puts it into perspective.
 
Seeing those numbers puts it into perspective.
It's interesting when we see guys say to return the gearing to stock. Which stock? And which one was the ideal one? I lean towards the 32rh.
 
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Your accurate tire size is the height of the hub x2.
I always have trouble with that definition of correct tire size since that would say that the engine rpms will vary based on how much air pressure is in the tire. To me, engine rpms are based on the rolling circumference of the tire which isn't significantly affected by the air pressure, within reason. To me, the deflected (based on how much air pressure is present) radius of a tire is not an accurate indication of the tire's rolling circumference which dictates how far it travels with each revolution.
 
I'm running 42rle, 3.73, 31", @65mph in OD 2000rpm
@65mph no OD 3000rpm
This 06 always gets the OD switched off when I get in.
 
I had 3.73 with 31" tires when I bought my LJ. I then installed 32" tires. Both sizes made the OD useless on speeds less thsan 55 MPH. I regeared to 4.88, and I usually turn the OD off when I'm cruising roads with a 45 MPH speed limit or less.
 
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I always have trouble with that definition of correct tire size since that would say that the engine rpms will vary based on how much air pressure is in the tire. To me, engine rpms are based on the rolling circumference of the tire which isn't significantly affected by the air pressure, within reason. To me, the deflected (based on how much air pressure is present) radius of a tire is not an accurate indication of the tire's rolling circumference which dictates how far it travels with each revolution.

It has proven accurate over and over again. And it can be verified by matching the rpm
I always have trouble with that definition of correct tire size since that would say that the engine rpms will vary based on how much air pressure is in the tire. To me, engine rpms are based on the rolling circumference of the tire which isn't significantly affected by the air pressure, within reason. To me, the deflected (based on how much air pressure is present) radius of a tire is not an accurate indication of the tire's rolling circumference which dictates how far it travels with each revolution.

It has been proven accurate over and over again. And it can be verified by matching the engine rpm to GPS speed. I've done both many times.

Measure the hub height. Double it to get your effective rolling diameter. Record your rpm at a gps measured speed. Everything will match up on Grimmjeeper or the calculator of your choice.

Blaine has explained this multiple times, btw.
 
With the plan to reagear when I go to 33s I did find myself with some follow up questions. Would the stock Dana 30 up front handle a lunch box locker and the 33s? I have read multiple times here that the 35 is dicey with 33s so I am already planning on upgrading to chromoly shafts for the 35 (I believe it's recommended the 1515h for that). I gave some thought to the super 35 but I like the idea of retaining my stock axles in case I manage to break the rear some day. I'm still undecided on a locker for the rear currently. All the reading I've done on here makes it very hard to decide. I'm leaning towards a selectable rear for it's on road manners and my preference for taking corners somewhat aggressively.
 
So I ran 33’s on 3.73 gears for a year. It wasn’t the end of the world. Ya it was a little doggy, but I just turned off overdrive every time I got in it and used the 42le effectively like it was a 3 speed. Now that I have 5.13 gears I do understand what I was missing out on.

I’m currently revolution 5.13 gears front and rear. Eaton e locker in the rear with a super 35 kit and a Yukon grizzly locker up front with revolution shafts.(the ones with the larger u joints) pretty good setup. It was a big chunk of money though for all the parts.
 
I'm leaning towards a selectable rear for it's on road manners and my preference for taking corners somewhat aggressively.
Yes to this. Leave the front open and do the super35 with a good locker. I'm removing my front lunchbox soon and putting a yukon zip in the rear. Should have done it that way all along. Leave the front open and it's rock solid, lock it and you open up a big can of worms.
 
I have TJ Sport 2004, with 42RLE and 3.73 gear ratio. I am running 31.5 inch tires (245/75R17). Overdrive is kind of useless, so i disable it when i get in. However, i am now installing new axles, with 4.56 gearing, which seems adequate for 31.5 inch tire. I agree that was not gearing correctly even in the stock form.
 
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So I just came back from a ride, in which I measured the speed and the RPM during 70MPH. My tires are 245/75R17, and they are aired down to 28 PSI.
At 70MPH, in overdrive, my RPM was at ~2050. This is with my stock axles. My understanding is that 31.5 inch tire, when aired down to 28PSI under TJ, will be really more like 30 inch maybe.
New axles that I need to install with 4.56 ratio, will bring up the RPM by 22% (4.56 -3.73 = 0.83, 0.83/3.73=0.22) so overall increase in RPM will be by RPMx1.22. In my case it will be 2050*1.22= 2440.
2440 RPM seems to be great RPM, and I believe that will drive much better.
 
So I just came back from a ride, in which I measured the speed and the RPM during 70MPH. My tires are 245/75R17, and they are aired down to 28 PSI.
At 70MPH, in overdrive, my RPM was at ~2050. This is with my stock axles. My understanding is that 31.5 inch tire, when aired down to 28PSI under TJ, will be really more like 30 inch maybe.
New axles that I need to install with 4.56 ratio, will bring up the RPM by 22% (4.56 -3.73 = 0.83, 0.83/3.73=0.22) so overall increase in RPM will be by RPMx1.22. In my case it will be 2050*1.22= 2440.
2440 RPM seems to be great RPM, and I believe that will drive much better.
I'm on 265/75R16s (31.6") and had 4.88s put in. Personally I would skip the 4.56 and go with 4.88s.
 
I'm on 265/75R16s (31.6") and had 4.88s put in. Personally I would skip the 4.56 and go with 4.88s.
I agree that 4.88 is in overall much better gearing with 4.0 and 42RLE, as it has some more room to growth with larger tires. However, i just a good deal on axles with lockers and 4.56 gearing, so decided to go with it. I believe that even 4.56 will be OK (maybe not ideal, but fully tolerable, especially here in this area of Texas that is flat as a tile) with 31.5 inch tires.
Also, i got dana 30HP with 4.56, it is not Dana 44 with larger ring and pinion. 4.88 is max ratio that Spicer intended to have in this Dana 30 axle - i am kind of thinking that i dont want to be in the max of the max gearing ratio. I would rather get Dana 44 in future, and then install 5.13 there, skipping the 4.88.
 
4.88 is max ratio that Spicer intended to have in this Dana 30 axle - i am kind of thinking that i dont want to be in the max of the max gearing ratio. I would rather get Dana 44 in future, and then install 5.13 there, skipping the 4.88.
First, 4.56 will be great with your 31's. But don't give any more worry to running 5.13 in a Dana 30, it's a very commonly installed ratio that causes no problems.
 
First, 4.56 will be great with your 31's. But don't give any more worry to running 5.13 in a Dana 30, it's a very commonly installed ratio that causes no problems.
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?
 
BTW, what RPM you are getting on flat highway at 70MPH?
I think it's in the 2600 range. 80 is getting close to 3k.

You make a valid point about terrain. The extra gearing helps me out in the hills. I spend a lot more time in 4th with the converter locked which is helpful for temps.
 
I think it's in the 2600 range. 80 is getting close to 3k.

You make a valid point about terrain. The extra gearing helps me out in the hills. I spend a lot more time in 4th with the converter locked which is helpful for temps.
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.