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should I just give in and re-gear?

3K views 23 replies 10 participants last post by  billiebob 
#1 ·
This is my 04 LJ.



I got it in early 2009 with 28k miles, and it now has just about 65k. Its an automatic with stock drivetrain.

Since I got it, I've added the Rally Tops 2 piece hard top, a mopar hitch, the Garvin rack, a set of Rubicon LJ rails, gas tank skid, belly skid, and a couple of other things I'm probably forgetting - but I figure at least 500lbs of additional weight that I added to it since I got it. And I put it on 31's. Its set up just the way I want it. Maybe some day I'd go to 33's and better rock rails, but that is probably the extent of the mods.

Its a 3rd vehicle that is mostly a weekend toy/ tow behind the RV to Moab and Death Valley/ explore local fire roads rig. I also do all of my fishing out of it because I can put my 8' 6" fly rod diagonally across the cab fully assembled and drive it comfortably in my waders! With the rack it also going to haul our 3 Hobie kayaks to our favorite high sierra lake (high clearance 4x4 only) for a few overnights in the summer.

But I digress. I've been pondering for a while that with the additional weight and larger tires, I might need to regear. I was headed out to Cabela's, slightly up hill on the freeway in a strong wind the other night and thinking the performance could be better. I am in Reno (elevation 4400 feet) and go up from there to play in the Sierra's.

It seems that I am turning the overdrive off more and more just driving around town to keep the RPMs in the over 1800 area. It seems like if I don't, the tranny shifts way too early and it bogs down going up hills.

Now I'm not complaining - its a Jeep and I love it. Just thinking that a regear might bring back some of the power and pep I'd like, especially when its carrying a load.

Its pretty rare that I'd take it on a highway trip of over 50 miles at a stretch, so I am will to sacrifice some 70 mph comfort for some low speed drive ability.

Any thoughts? And if I did regear, 4.10 seems like its not far enough, and 4.56 seems to far. 4.27? (if I can find it for the D-30)

Thanks in advance!
 
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#5 ·
If you plan to have 33"s at some point, you might want to go higher than 4.10/4.11. Check out your options on the Grimjeeper gear calculator. For example, I have a 2004 TJ, the same 42rle, and am on 30's. I could feel some loss of usefulness of the OD when I put those on. With 4.10/4.11 instead of my 3.73, I would be at pretty much the same RPM's with the 33"s. So its acceptable, but not great. I am not sure that I would ever actually go to 33"s however. And if I did I would have probably 29"s in a winter tire to preserve the winter highway performance, so going to a recommended gearing for 33"s with the 42rle would be like 4.88 and would not be great with that smaller winter tire. Just something else to consider.

Gear Ratio Calculator
 
#24 ·
True but... as the op says...

"I was headed out to Cabela's, slightly up hill on the freeway in a strong wind the other night and thinking the performance could be better. I am in Reno (elevation 4400 feet) and go up from there to play in the Sierra's."

Only a turbo can return sea level performance in the mountains. With no desire to get anything bigger than 33s I think a turbo is a better choice.

He already has 3.73s and his tires are stock. He needs forced induction more than a regear for his application.
 
#11 ·
Thanks All - makes sense. I was a little concerned about the 4.56 but think that's the way to go.

Thanks for the tip on the grimmjeeper tool. Helps me visualize when I'd be back on the power band.
 
#12 · (Edited)
4.56 is NOT enough gear for 33's and the 4-speed automatic. Trust me, 4.88 is the correct ratio for your particular transmission. YES 4.56 would be more appropriate for some other transmissions like the 5-speed manual. 4.10 would be more appropriate if your transmission was the older 3-speed automatic. But for your 4-speed 42RLE automatic which has a very steep .69 overdrive ratio, you really need 4.88 for 33's. Really. Those who would push 4.56 on you for 33's don't know/understand the characteristics of your 42RLE transmission. And yes, that ratio is what you want for the street... I'm not recommending 4.88 for offroad reasons.
 
#13 ·
so that brings up an interesting point. I've got a nice set of Toyo 31's on it right now (the ones in the pic) and I have to say I'm pretty happy with those. If I just stick with 31's for the foreseeable future, would the 4.56's be the right choice?

Or asked another way, would 4.88's be to much if I never went above 31's?
 
#14 ·
For 31's, that'd be a tough decision. 4.56 would be a little steep for that size tire and while 4.10 would be ideal, it wouldn't be enough different from your current 3.73 to warrant the cost of regearing. Due to the significant cost of regearing, I'd probably stay with the stock gearing until/if you get to 33's.
 
#15 ·
Jerry, a friend of mine traded his Jeep in after we stripped much of the aftermarket Savvy/Currie stuff off (some of which is now on my jeep :lmao:). He was running 33s & 4.88s. After we stripped the stuff off, he was running 30s with 4.88s for over a week before trading it in. He said it didn't feel nearly as overgeared as he expected it would...he said it was fun to drive, almost like a manual Jeep....feeling "peppy". Worked fine on the highway too, his daily commute was 60+ miles each way.

For 31s, 4.27s would be mathematically ideal, but those don't exist. I suspect 4.56s would be perfect with 31s with the 42RLE. People do run 5.13s with 33s and find it better than 4.88s. This is a similar comparison. I do know from personal experience 31s & 3.73s blows monkey balls, especially with a heavily loaded LJ.
 
#18 ·
I you want to see just how tall that OD is here are a few tables so that you can see the rpm/mph speed ranges. I threw in the same year manual tranny just so the the folks with a manual could see the difference between a manual and an auto.

Happy Trails
Bob
 

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#19 ·
Ok - this is helping clarify things - thank you.

So with the O/D off, what is the trans ratio? Is it then the 1:1?

I'm trying to visualize where I am on the chart with the O/D off.
 
#20 ·
With overdrive off trans 3rd in auto with torque converter locked is 1;1 and if torque converter unlocked there is slight slip

So your rpm at 60 mph

5280*12 * Diffy ratio *tranny ratio/(3.14 *tire diameter)

So with OD off tranny ratio is 1 and Diffy ratio is 4.11 or 4.56 ect
 
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