32's and the 3.07 rear diff


WestCoastDan

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added 2.5" RC lift to our '03 4.0
Upgrading to 32" BFG A/T's

I know the speedometer gear will need to be changed to keep the gauge accurate w/ this configuration.
What is the most appropriate "upgrade" to the rear end to regain the freeway speed that I expect to lose?

This is a daily driver, not a serious off road vehicle, so I'm not looking for anything outrageous, just the most appropriate configuration for these new 32's.
 

DaYooperTransplant

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My 97 had 32's with the 3.07, when I bought it. It wasn't horrible.

A member on here found me some 4.10 axles, so I swapped them out, and it was a huge improvement. I have the manual AX15, and in 5th gear I have no issues holding 70mph. I have a 2" SL and an 1 1/4" BL. The speedo gear swap was easy too.

There are better choices out there though, hopefully some one chimes in with them. But if you search around in this forum you'll find your answer. Many owners have the same question about gears vs tire size. Good luck.
 

machoheadgames

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If I were buying gears for the job it would be 4.56 for 32's assuming manual trans. I'm guessing you have a 4.0 NV3550 based on the fact that your gears are 3.07. Pretty certain the 4 speed auto never came with 3.07s.

Anyways, make sure 32's are what you really want long term before you buy gears for them. If I were going to 33's with the manual it would be 4.88 and 5.13 for 35's.
 

Fishtaco

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You have to re gear both front and rear you cant just do the rear. If you are coming from 31,s? I cant see you noticing much difference with 32,s? but I cant really say as I run 29,s with 3.07 gearing and not interested in re gearing at this stage so wont go above 31,s

A girl on our local FB TJ forum a few months ago was pretty upset because everyone around her told her to go 33,s for her first mod when she got her TJ but nobody asked what gearing or lift it had and in the end she didn't have the money for the unsuspected re gear after spending out on the wheels and tires first, You don't immediately realize any possible impact on your TJ as a "DD" will be because everyone else seems to be running bigger tires and a lift but:
I dont see any talk about bigger tires and re gearing V worn engines! maybe there is no effect? because I have not gone down that road to tell but these things are getting old now and it is evident by this forum word that one change can cause compound problems needing more changes which may not suit a DD.
29,s/30,s on no lift looks as proportionate as 31,s /32,s on a 2 inch lift plus a stock TJ was built with excellent off road capability.

Whats an inch or 2? said the nun to the candle maker! just give me the cheap fat ones :)
 
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machoheadgames

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You have to re gear both front and rear you cant just do the rear. If you are coming from 31,s? I cant see you noticing much difference with 32,s? but I cant really say as I run 29,s with 3.07 gearing and not interested in re gearing at this stage so wont go above 31,s

A girl on our local FB TJ forum a few months ago was pretty upset because everyone around her told her to go 33,s for her first mod when she got her TJ but nobody asked what gearing or lift it had and in the end she didn't have the money for the unsuspected re gear after spending out on the wheels and tires first, You don't immediately realize any possible impact on your TJ as a "DD" will be because everyone else seems to be running bigger tires and a lift but:
I dont see any talk about bigger tires and re gearing V worn engines! maybe there is no effect? because I have not gone down that road to tell but these things are getting old now and it is evident by this forum word that one change can cause compound problems needing more changes which may not suit a DD.
29,s/30,s on no lift looks as proportionate as 31,s /32,s on a 2 inch lift plus a stock TJ was built with excellent off road capability.

Whats an inch or 2? said the nun to the candle maker! just give me the cheap fat ones :)
There is no issue of worn engines with regearing. If anything the engines only benefit from it. Many folks don’t understand the physics behind leverage. A regear gives the engine more leverage against the tire which means the engine is seeing less load. It may spin faster but it has less load being exerted against the engine which decreases the wear of any moving parts per revolution. Lots of people assume “1 rotation of the engine equals a specific amount of wear so going to a higher rpm kills your engine more quickly” - yeah, no, doesn’t work like that. There are different amounts of wear per rpm depending on the load the engine sees and a regear lowers that load despite the higher speed the engine turns. Plus, the engine has oil which keeps everything moving with nearly no resistance. If a regear and the higher rpm was actually wearing things out (as in wearing out crank bearings from the extra rotations), you would know it pretty soon from the eventual 0 oil pressure from your dead worn out bearings.

Another way to think about it is towing a trailer. A trailer is heavy and adds a lot of weight, which is a lot of extra load on the engine. But the rpm isn’t higher, so this would mean all the people who think X amount of wear per rpm would mean that towing the trailer wouldn’t increase wear right? Wrong they are, because once again the load per rpm is higher in this case, so a higher rpm with less load would wear the engine at a slower rate.

My final example is the 3 speed auto TJ. Plenty of those came from the factory with 3.73 gears and 28-30” tires. You can do the math, but 75 mph with 28” tires is about 3357 rpm, or even more when the tire doesn’t measure up to its advertised height. So you’ve got thousands upon thousands of these Jeeps from the factory revving higher than really any of the manuals, even when the manuals regear. And yet you never hear of a blown engine due to the auto, or anything like that. If anything, there have been quite a few Jeep mechanics over the years share that the engines they open from the 3 speed auto Jeeps actually have cleaner cylinder walls than the 3.07 Jeeps that always revved low their whole life.

In short, regearing is not hurting anything. If your engine blows up after a regear you can rest assured that problem was already starting before the regear.
 

97' 4 Popper

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Many will mention they run those gears with 32s no problem. I will chime in with my experience driving undergeared with 3.21s 32.5s and a 32rh. Yea sure it's liveable and yea you can reach 90 but that's besides the point. You will be one of the slowest vehicles in the world when the light turns green. I personally would never make the jump to a tire size greater than 31 without some plan to regear. I went from 30s to 31s on my lj with 3.73s and it only made a slight difference but I'm such a snob now I want 4.10s or even 4.56.
 

Tob

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To add a data point for you, I am on 265/75 16 (31.6”) tires with 4.10 gears and the NV3550 5-speed and I love it. But I live on the gulf coastal plain where there is nearly zero elevation change. If I moved to even a slightly larger tire size or lived somewhere with hills and lots of elevation change, I would want to regear.
 
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Fishtaco

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How fast are you planning to drive?

I can reach 85 on my 97 with 3.07 gears no problem. 31" tires. Would not want to drive faster in a Wrangler, regardless of gearing.
Off road advantages aside it must be the different ways people drive or their road topography? I have no problem with my 3.07 gearing and I doubt if I went to 32,s it would make much noticeable difference but I suppose its the way I drive it and where I live?
I live in the city so I have a lot of lights to contend with so forever changing gear but have no problems reaching freeway merging speeds alongside any other vehicles and maintaining higher speed limits, it drives perfectly fine to me as a DD.
I believe top end speed is slightly greater with higher gears like 3.07 but achieving top speed is quicker with lower gearing.
I suppose if the engine doesn't labour in gear and you are not constantly needing to change down then there is nothing wrong with 3.07 gearing even on 32,s if it suits a persons driving manner and road conditions.
 

Tob

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Off road advantages aside it must be the different ways people drive or their road topography? I have no problem with my 3.07 gearing and I doubt if I went to 32,s it would make much noticeable difference but I suppose its the way I drive it and where I live?
I live in the city so I have a lot of lights to contend with so forever changing gear but have no problems reaching freeway merging speeds alongside any other vehicles and maintaining higher speed limits, it drives perfectly fine to me as a DD.
I believe top end speed is slightly greater with higher gears like 3.07 but achieving top speed is quicker with lower gearing.
I suppose if the engine doesn't labour in gear and you are not constantly needing to change down then there is nothing wrong with 3.07 gearing even on 32,s if it suits a persons driving manner and road conditions.
I think part of it is that people don't know what they don't know. My first TJ had 33.8" tires on 3.73 gears from the previous owner with the same 4.0 and NV3550, and having never driven a TJ nor having much driving experience in general, I though it was just fine. But when I test drove my current TJR with 4.10's and 31.6" tires, it felt amazing.
 

Fishtaco

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I think part of it is that people don't know what they don't know. My first TJ had 33.8" tires on 3.73 gears from the previous owner with the same 4.0 and NV3550, and having never driven a TJ nor having much driving experience in general, I though it was just fine. But when I test drove my current TJR with 4.10's and 31.6" tires, it felt amazing.
Amazing in what way is it quicker? Where I live I cant go quicker, we have speed cameras on almost every traffic signal and fixed speed camera's on freeways/highways with some of the lowest top speed limits in the world and they keep lowering them so you get done by those cameras, soon to be coming to a town near you to pay for covid lol

I now have 7 speed/red light combo traffic signals in the 10 mile trip to work with random autonomous speed cameras on enclosed trailers that pop up anywhere anytime and traveling random speed cameras in the back of un marked pickups that move from place to place all day!
 
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Tob

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Amazing in what way is it quicker?
Not top speed. In the first TJ, I would lug the engine badly, even when not under much load. Having the appropriate gearing to use the correct RPM range of the engine feels much better. It’s easier to take off from a stop without having to slip the clutch so much. Better acceleration. That combined with the smaller tires and lower ride height made the second TJ feel planted and agile in comparison.

Worst TJ I ever test drove was a Sahara on 33’s with 3.07 gears. Awful, even with the 6-speed NSG-370.
 

Fishtaco

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Not top speed. In the first TJ, I would lug the engine badly, even when not under much load. Having the appropriate gearing to use the correct RPM range of the engine feels much better. It’s easier to take off from a stop without having to slip the clutch so much. Better acceleration. That combined with the smaller tires and lower ride height made the second TJ feel planted and agile in comparison.

Worst TJ I ever test drove was a Sahara on 33’s with 3.07 gears. Awful, even with the 6-speed NSG-370.
As I said I have no problem with my 3.07,s maybe because I have driven 6 wheelers most my 40 odd year driving life and don't actually expect my TJ to drive like a modern stop go rice grinder? I mastered road speed match to up or down shift change years ago so for me its easy to drive the TJ on the 3,07,s without any issues, you just need to know a vehicles capabilities and limitations, I swap from Auto to Syncro to Road Ranger weekly! am I a good driver ?I dont thinks so But I am a responsible driver! I have never thrashed a vehicle in my life :)
 

97' 4 Popper

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As I said I have no problem with my 3.07,s maybe because I have driven 6 wheelers most my 40 odd year driving life and don't actually expect my TJ to drive like a modern stop go rice grinder? I mastered road speed match to up or down shift change years ago so for me its easy to drive the TJ on the 3,07,s without any issues, you just need to know a vehicles capabilities and limitations, I swap from Auto to Syncro to Road Ranger weekly! am I a good driver ?I dont thinks so But I am a responsible driver! I have never thrashed a vehicle in my life :)

This has nothing to do with driver ability 3.07s are a garbage ratio even for stock tires like 28s and no one would ever suggest it if they drove TJs that had the proper gearing. You have driven properly geared TJs before, right?
 
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machoheadgames

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This is absolutely a case of not knowing what you don't know. Anything is fine until you try something better. A 3.07 Jeep simply can not use 5th in the majority of situations on a normal 31-35" tire no matter how you spin it. Downhill, maybe. The rpm levels are just too low, even in 4th gear to really be useful much of the time. Nothing says anyone regearing their Jeep has to absolutely race stoplight to stoplight like a modern ricer. That is not why people regear, although the regear certainly enables you to do that if you so choose. It just overall makes the rig drive much better with much less effort, and that doesn't change whether you started driving yesterday or 50 years ago. It just plain drives better with a regear and it really isn't debatable. No amount of driving experience will ever change that. It's made obvious simply by how much better you can slip the clutch off idle without bogging it down.
 

fwgump

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Many will mention they run those gears with 32s no problem. I will chime in with my experience driving undergeared with 3.21s 32.5s and a 32rh. Yea sure it's liveable and yea you can reach 90 but that's besides the point. You will be one of the slowest vehicles in the world when the light turns green. I personally would never make the jump to a tire size greater than 31 without some plan to regear. I went from 30s to 31s on my lj with 3.73s and it only made a slight difference but I'm such a snob now I want 4.10s or even 4.56.
OK... I have a 1997 TJ for my wife just bought her 255/75R17 which are equal to 32" with a 2.5L i am thinking of 4.88 gears.
Thoughts from a similar experience. Thanx
 
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97' 4 Popper

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OK... I have a 1997 TJ for my wife just bought her 255/75R17 which are equal to 32" with a 2.5L i am thinking of 4.88 gears.
Thoughts from a similar experience. Thanx
In this thread we have been posting under the assumption that the reader has a 6 cylinder. For your 2.5 with 32s some may disagree but I believe you will want the deepest your axle can go. Back when I had my 97 4 cylinder 5 speed it was 31s and stock 4.10s that was undergeared. I personally would run 31s with 4.88. With 32s I would do 5.13.
 

fwgump

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In this thread we have been posting under the assumption that the reader has a 6 cylinder. For your 2.5 with 32s some may disagree but I believe you will want the deepest your axle can go. Back when I had my 97 4 cylinder 5 speed it was 31s and stock 4.10s that was undergeared. I personally would run 31s with 4.88. With 32s I would do 5.13.
Wow... What if we where to go 33" in the future? 35" would be to large for the 2.5 correct? I just bought the jeep last week and who know where one will go in the future... Its a sickness.
 
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