Help me settle the regear ratio question

[Kreepin1]

He has the tires but they aren’t on the Jeep yet. The only “experiment” you can do is change the gears out. No calculator is going to tell you the end result.

Ah, I missed that. In that case I agree with you and he's wasting his time with the stock tires.

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[omnitonic]

I did a lot of experimenting and it did give a decent feel for what it would be like in 6th with 4.56. But the good news is that after the swap it is even better... There are other differences, such as the ratio change when dropping to 5th to pass... I was waffling between 4.56 and 4.88 on 35's...

Guilty as charged. I've been waffling hard. I have done enough homework several times over, and it's time to choose. I definitely feel like 4.56 is where to place my bet, and I appreciate all the feedback and input I've gotten from this thread.

I'd also like everyone to know that a lot of my yammering on this has just come from boredom. I'm walking past a stack of gorgeous wheels and tires, but I haven't had time to put everything together yet. I will get it done soon, and then I will get the regear done ASAP, but it's still going to be at least a month before the guy can get me in the shop.

 

[Kreepin1]

Guilty as charged. I've been waffling hard. I have done enough homework several times over, and it's time to choose. I definitely feel like 4.56 is where to place my bet, and I appreciate all the feedback and input I've gotten from this thread.

I'd also like everyone to know that a lot of my yammering on this has just come from boredom. I'm walking past a stack of gorgeous wheels and tires, but I haven't had time to put everything together yet. I will get it done soon, and then I will get the regear done ASAP, but it's still going to be at least a month before the guy can get me in the shop.

You might want to put them on your Jeep and repeat the experiment before you make up your mind...

 

[DanW]

The thing that none of these gear calculators, and no amount of nerding (unless you have a wind tunnel) can account for, is drag. Rolling mass of the larger tires and more drag from your now taller Jeep. The gearing in the stock MT rubicon is pretty poor. I can’t even imagine the manual with 3.45s. I ran my 6 speed rubicon on 37s around for about a year before changing to 5.13s and couldn’t be happier. Mileage improved, 5th and 6th are back, and it’s just a hell of a lot more fun to drive. There is no way I would even consider 4.10s if I were you. 4.56 if you want the best on road performance. 4.88 if you want the best trail performance. All the calculators be damned.

Actually, mine did just fine off-road with 4.10's and 35's. It was on the highway where it suffered, mainly in 6th gear. It's pure joy on the highway now, though, with 4.56. I can accelerate and pass now without downshifting.

If I lived near mountains, like you, I'd have gone 4.88's, for sure.

You are right about all the variables. But the calculators will get you in the ballpark.

 

[DanW]

He has the tires but they aren’t on the Jeep yet. The only “experiment” you can do is change the gears out. No calculator is going to tell you the end result.

It gets close. It was helpful to me. It turned out a little better than the calculator showed, but still pretty close.

 

[word302]

Actually, mine did just fine off-road with 4.10's and 35's. It was on the highway where it suffered, mainly in 6th gear. It's pure joy on the highway now, though, with 4.56. I can accelerate and pass now without downshifting.

If I lived near mountains, like you, I'd have gone 4.88's, for sure.

You are right about all the variables. But the calculators will get you in the ballpark.

Yeah but don’t forget you have a much lower low range than he does.

 

[DanW]

Yeah but don’t forget you have a much lower low range than he does.

You are correct. I had in my head 4.0:1 low range and forgot the standard is what, 2.73, I think? I can see how that would be a whole different ballgame.

 

[omnitonic]

You might want to put them on your Jeep and repeat the experiment before you make up your mind...

That's definitely going to happen. I will be running the 35s on the 3.45s for at least the next month or so, and maybe longer. I'm definitely going to put them on ASAP. I may try running them on my Rubicon takeoff suspension once I get the high clearance front fender flares installed later today. If that doesn't look plausible, I should get the lift done next Sunday. I know the game plan, and basically did most of it once already, so I should be good.

The most important component I'm waiting on is a Rock Krawler front track bar.

Yeah but don’t forget you have a much lower low range than he does.

Having the 2.72 transfer case is definitely going to make off-roading on 3.45s and 35s a bit disappointing. I really hope I can get the regear knocked out before the autumn rain turns all those dirt roads into muddy nightmares. I'm looking forward to the autumn rain. Right now, everything is so dry you could drive it on a stock half ton truck on street tires, and that ain't no fun.

 

[omnitonic]

The sad thing is once I started thinking about my 2.72 transfer case and all the places I need to go slow, I started thinking about 4.88s.

I'm currently spending a lot of time turning about 2500 RPM, and my gas mileage is fine. That's all I'm turning on 4.88s.

Hmmm. @grimmjeeper's calculator is a bit buggy in the transfer case area. I changed it to 4, and nothing updated. Then I changed it to 937, and I'm very sure nothing updated. Seems like you have to update the gear ratio or some other widget before the calculator picks up changes to these fields.

Anyway, on a 2.72 transfer case, the difference between 4.56 and 4.88 is pretty insignificant, and there is no real off-road benefit to making what would surely be a dramatic on-road sacrifice.

Blah Blah, yeah, I got bored again. Sorry guys. I love you guys. ?

 

[Jteakus]

If you are gonna use it offroad, gear it where you don't need to use the clutch in first gear. Take into consideration you have a 2:72 low range. You have a 6-speed, use that 6Th gear! Most of us usually go bigger the next time we buy tires. Consider 4.88's.

 

[DanW]

That's definitely going to happen. I will be running the 35s on the 3.45s for at least the next month or so, and maybe longer. I'm definitely going to put them on ASAP. I may try running them on my Rubicon takeoff suspension once I get the high clearance front fender flares installed later today. If that doesn't look plausible, I should get the lift done next Sunday. I know the game plan, and basically did most of it once already, so I should be good.

The most important component I'm waiting on is a Rock Krawler front track bar.
Having the 2.72 transfer case is definitely going to make off-roading on 3.45s and 35s a bit disappointing. I really hope I can get the regear knocked out before the autumn rain turns all those dirt roads into muddy nightmares. I'm looking forward to the autumn rain. Right now, everything is so dry you could drive it on a stock half ton truck on street tires, and that ain't no fun.

It may not be terrible in low range. It depends on the kind of wheeling you do. If rock crawling, yeah, it'll be a bit tall. But I've found that when not crawling, I'm often in 3rd and sometimes even 4th gear. So consider that in the mix, too.

Btw, if you re-gear, I'd advise Dana/Spicer rings/pinions and overhaul kits (bearings). Mine are quiet as can be and you know Dana won't give the wrong specs, as we may have seen with a couple other brands (not Yukon, to my knowledge). I've heard good things about Yukon, but I decided on Dana/Spicer because they are the original equipment manufacturer that designed the specs in the first place. There wasn't much difference in price, either, at least compared to Yukon.

 

[sanman357]

The sad thing is once I started thinking about my 2.72 transfer case and all the places I need to go slow, I started thinking about 4.88s.

I'm currently spending a lot of time turning about 2500 RPM, and my gas mileage is fine. That's all I'm turning on 4.88s.

Hmmm. @grimmjeeper's calculator is a bit buggy in the transfer case area. I changed it to 4, and nothing updated. Then I changed it to 937, and I'm very sure nothing updated. Seems like you have to update the gear ratio or some other widget before the calculator picks up changes to these fields.

Anyway, on a 2.72 transfer case, the difference between 4.56 and 4.88 is pretty insignificant, and there is no real off-road benefit to making what would surely be a dramatic on-road sacrifice.

Blah Blah, yeah, I got bored again. Sorry guys. I love you guys. ?

I think you should go with the 4.88s. I’m on 315’s (35s) now with 4.10s 6mt, JLUR. No lift. And it looks like it was supposed to come that way. 6th gear is useless until your over 70. And if you decide on 37s in the future your already where you should be. And if I remember correctly the Manual Extreme Recon package is supposed to have 4.88s vs 4.56s for the Automatics.

 

[DanW]

I think 4.56 and 4.88 are actually pretty close, so I don't think you can go wrong either way. But I agree with @sanman357 that if you even have a 1% chance of going to 37's you should probably go with 4.88. I just felt that here in the flatlands I didn't want 6th above 2500rpm at 75mph. I also didn't want 1st gear redlining at under 25mph, either. If I lived in the mountains, I might have gone 4.88, but 4.56 would still be fine.

As for 35's, I LOVE where it put 6th gear. It is perfect, for me, holding speed on hills and able to be used down to 55mph, but still returning good fuel economy. And 1st gear is as short as I would possibly want it. As for crawling in 1st gear and low range, it is insane. I think it can move slower than a glacier and could idle up a 30 degree climb with the air on. I can't even imagine 4.88/manual with 100:1 crawl ratio. I'm guessing mine is at or about 90:1 now, which bests the original factory 84:1 with 4.10's and 33's, and it was fine with 4.10's and 35's. (I'm guessing around 76:1)

Anyway, I'd say go either way with 35's. If thinking of 37's at all in the future, go 4.88's. But you'll be MUCH happier either way than what you've got, even with 4.56/37" combo.

 

[grimmjeeper]

Hmmm. @grimmjeeper's calculator is a bit buggy in the transfer case area. I changed it to 4, and nothing updated. Then I changed it to 937, and I'm very sure nothing updated. Seems like you have to update the gear ratio or some other widget before the calculator picks up changes to these fields.

Huh. I'll look into that.

 

[Some Random Guy]

That's definitely going to happen. I will be running the 35s on the 3.45s for at least the next month or so, and maybe longer. I'm definitely going to put them on ASAP. I may try running them on my Rubicon takeoff suspension once I get the high clearance front fender flares installed later today. If that doesn't look plausible, I should get the lift done next Sunday. I know the game plan, and basically did most of it once already, so I should be good.

Ask your regear shop if big tires void the warranty during break-in. Mine did. Anything over 33” is not warrantied due to being broken in hard by Randy’s Worldwide (AKA Yukon).

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