What gear ratio should I install in my Jeep Wrangler TJ / LJ? (and other re-gearing FAQs)
- Thread starter Chris
- Start date
I installed the transmission cooler from derale. When used with correct gearing, and derale, 42RLE does not overheat at least for me.
With 4.56 and 30 inch tires, I am at 2750 RPM at 75. I would say that it is good enough. The problem with going deeper, is that on flat surfaces of Texas, you start to have really high RPM for 75MPH, and you don’t really need it.
I disagree that it is an irritating transmission. It is better than the previous 3 speed, because of overdrive. Just need to gear it correctly. With correct gearing ( which almost nobody have) it works as charm.
The folks who recommend 4.88 for 33s don’t know what are they talking about. I have 4.56 (very close to 4.88), and 31 is the maximum that you can do without loosing power.
You need to have at least 2500RPM for 70MPH. The overdrive ratio is 0.69, so it shifts into overdrive, you get easily into not enough RPM to accelerate the rig.
it is hard to imagine how much more enjoyable the ride in TJ 4.0 with 42RLE with 30 inch tires and 4.56 is, compared to 3.73 for example. The acceleration with overdrive off is amazing. Even on highway with overdrive on, if still goes great.
If I would reheating TJ with 42RLE, i would go straight to 5.13 (cannot go higher on non rubi) and run up to 33 maximum.
TJ is my daily, so I am sensitive to how it accelerates in traffic.
Good enough would be better if you were pushing 5.13.
42rle/29.75”/5.13=2998rpm @ 75mph
Hasselblad
TJ Enthusiast
I would add that HP Tuner fixing the shift points helps a ton as well.
Only on 05-06 TJs. I'm stuck with the irritating factory shift points.
Hasselblad
TJ Enthusiast
Did wonders on my 06. Since it doesn't have the mechanical kickdown, the tuner solved that as well. Being able to tromp the pedal to get out of the lug is wonderful.
Did wonders on my 06
I have no doubt that changing the shift points makes a noticable difference. What I do know is that the .69 OD is a problem that cannot be addressed on a TJ. Mine is supercharged pushing 5.38s on 35s and even the extra horsepower is not quite enough to make me stop being irritated by how steep it is.
Yeah, but with all that flat and 2 degree slopes to the horizon, you don't really give a shit. Get some place where you are driving on something other that the salt flats endlessly and it starts to matter a whole bunch more.
That is more telling than you know. There is nothing you can do to stop that from being an irritating piece of mechanical poo. The best we wind up with is not wanting to carry a pistol around when we drive so we can shoot the damn thing and put it out of its misery. The only reason that doesn't happen with more regularity is ammo is expensive.
Yes, I am aware that you are geared appropriately for the 30" tires. If you run the numbers out, a gear step for each tire size step, where does that put you on larger tires? 4.88- 31-32, 5.13- 32-33, 5.38- 33-35. I think there is a case to be made for 5.60's out there somewhere and see how those would do on 35's.
Did someone steal your OD off switch?
Did wonders on my 06. Since it doesn't have the mechanical kickdown, the tuner solved that as well. Being able to tromp the pedal to get out of the lug is wonderful.
Hasselblad
TJ Enthusiast
Going up the long steep grades, turning off OD did nothing whatsoever before. If the cars in front went below a certain speed and the RPMs dropped it killed the jeep without the kickdown and doomed the TJ to ~50MPH. It wasn't solely the OD that sucked the life out of the jeep. The regear next week should make the issue disappear entirely. The tuned shifts will be icing on top.
Edit: I am sure the overall tune had more than just the shift points to thank for the improvement
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I think 5.89s would be basically perfect for 35's with the 42RLE. It's the barrier to entry that sucks about them, though. You need dual 44's to run them, which of course bolt-in is only available from a Rubicon, AND THEN you have to buy aftermarket lockers to run the gears in the Rubi axles. Ends up being quite an expensive project for 9% gear reduction beyond 5.38s. Plus then of course dealing with the almost inevitable driveline complaints that will arise from the new higher speeds, unless you're lucky.
35s on 5.89 would be around 2850rpm @ 70 and 3050rpm @ 75. 4130 & 4430 in 3rd gear, respectively, giving around an 85 mph top speed in 3rd for passing, at which point you would have to go into OD since you run out of rpm at redline.
35s on 5.89 would be around 2850rpm @ 70 and 3050rpm @ 75. 4130 & 4430 in 3rd gear, respectively, giving around an 85 mph top speed in 3rd for passing, at which point you would have to go into OD since you run out of rpm at redline.
The big unknown with 5.89s, now that we finally know it can be done, is what the resulting driveshaft rpms mean for the harmonic vibrations frequently found on 42rle/np241 drivelines. There might also be a concern with the ring and pinion being that low in a Dana 44. I had to opportunity to be the first to do it all a few years ago, but did not want to be the guinea pig on that big of a gamble.
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Anyone running 4.56 or 4.88 with a 4.0 and NV3550 on 35s? Feedback on real world driving please. No offense to anyone but I don't really care much about gear ratio charts and graphs as much as I care about the real world driving experience feedback from actual Jeep owners running this combo. Thank you! 
I am targeting my gearing for comfortable daily driving in 2HI. Not doing any crazy trails, so Low gear (NP231) is working well for me, like in Bend Bend national park.
Understanding what I understand today, I would use the following gearing of (4.0, 42RLE):
1. 4.56 for 30 inch tires - 2552 RPM at 70 MPH
2. 4.88 for 31 inch tires - 2640 RPM at 70MPH
3. 5.13 for 32 inch tires - 2668 RPM at 70 MPH
4. 5.38 for 33 inch tires - 2778 RPM at 70 MPH
I assume that with increase in tire size, also target RPM needs to be a little higher, to compensate the increase in the tire size.
2 cons for re gearing deeper:
- Dana 35 - when we go into deeper gears, it increases the strain on the shafts, and dana 35 are not known for their strength. So, I would not go into any deep gears on Dana 35.
- Driveshaft vibrations - deeper gears increases the chances of getting into these, of geometry and driveshaft angles are not ideal, IMO.
1 major point for 42RLE re gearing deeper:
- with deeper gears, it tends to generate less heat. At least this is what I see going from 3.73 to 4.56.
You are falling into the trap of thinking that the deep gearing we advocate for is because of crazy trails. We argue for it because of the highway. Once you do that, everything else is also in favor of the trails.
I don’t have complaints about vibes with the 589’s and 35’s, but they are there. I asked my wife if she felt the vibrations and she said “no.” I can feel them though. It’s not terrible, but I’m the survey sample size of 1.
Also now I’m the guinea pig for how the ring and pinion hold up off-road. At where I am the issue becomes a fusible link and keeping that at the u-joints. Thus, the questionable move to RCV’s which could move it inside the diff..
At least on flat highways of Houston metro, the below combo works fine. Other places (a lot of hills or mountain roads) I would go much deeper.
1. 4.56 for 30 inch tires - 2552 RPM at 70 MPH
2. 4.88 for 31 inch tires - 2640 RPM at 70MPH
3. 5.13 for 32 inch tires - 2668 RPM at 70 MPH
4. 5.38 for 33 inch tires - 2778 RPM at 70 MPH
Also, for some reason I think that 90% of folks with 4.0 and 42RLE do no gear even that deep and are stuck with stock gearing like 3.73 or 4.10
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