Regearing Questions? READ THIS!

[schmiedel]

In fact, I have the following info:

4.0L I6 MPI "Power Tech" - 177HP @ 4750rpm, 220lb-ft @ 4000rpm
4.0L I6 MPI "Power Tech HO" (High Output) - 190HP @ 4750rpm, 220lb-ft @ 4000rpm (91-95), (96-01) has 225lb-ft @ 3000rpm

This means that the older 4.0 engines have the maximum torque at higher revs, which means deaper gears will improve the final power output, but they will also drop the max-speed in 5 th gear in the manual if I'm not mistaken. Does anyone have the gear ratios for the AX15 transmission? This way it could be possible to know the exact revolutions for each speed / gear for tire-size and gearset combination (a little bit of work but it might be worth it).

Regards

 

[Menzenski]

Does anyone have the gear ratios for the AX15 transmission?

1st - 3.83
2nd - 2.33
3rd - 1.44
4th - 1.00
5th - 0.79

 

[schmiedel]

OK, I will share a few calculations I did:

All are for the manual tranny, I'll start with 30 tires:

5000RPM speeds for (in kph, divide by 1.6 to get mph):

gear 1 sp 2 sp 3 sp 4 sp 5 sp 1LO 2LO
3.07 61 100 164 234 296 22 37
3.55 53 87 141 202 256 19 32
3.78 50 82 133 190 241 18 30
4.1 46 75 122 175 222 17 28
4.56 41 68 110 157 200 15 25

now the same for 3000rpm:

gear 1 sp 2 sp 3 sp 4 sp 5 sp 1LO 2LO
3.07 37 60 98 140 178 13 22
3.55 32 52 85 121 154 12 19
3.78 30 49 80 114 144 11 18
4.1 27 45 73 105 133 10 17
4.56 25 41 66 94 120 9 15

So, with 30 tires it seems to work quite well for 4.1 gears, as you would get a max speed @5000rpm of 222kph (almost 140mph which is far more than I would dare to drive my XJ). Though, the speed for driving at 3000rpm is still around 130kph, (around 80mph), which all seems to work fine. In 1st gear and 4lo, you would start to get torque driving at 10kpn, which is more or less 6mph, and it looks alot better than the 13kph you get on 3.07 gears.

I will post the same results for 33 tires, if anyone is interested:

At 5000rpm:

gear 1 sp 2 sp 3 sp 4 sp 5 sp 1LO 2LO
3.07 67 110 180 257 326 25 41
3.55 58 96 156 223 282 21 35
3.78 55 90 146 209 265 20 33
4.1 50 83 135 193 244 18 30
4.56 45 74 121 173 220 17 27

At 3000rpm:

gear 1 sp 2 sp 3 sp 4 sp 5 sp 1LO 2LO
3.07 40 66 108 154 196 15 24
3.55 35 57 93 134 169 13 21
3.78 33 54 88 125 159 12 20
4.1 30 50 81 116 147 11 18
4.56 27 45 73 104 132 10 16

So, 33 tires will really ask for 4.56 gears, so this calculations might tell you that you shouldn't use stock axles for 35 tires or bigger?

Well, I made these calculations with a simple Excel sheet. If anybody is interested in it, I would attach it but I think you can't do this on this forum. I could send it per mail still. If you find some errors, please let me know to fix them.

Regards

 

[Phil]

In GENERAL, on a 4.0 that is in good condition, you want to keep the revs at or below 3,000 at max cruising speed. ... If you have the unfortunate experience of owning a 4 cylinder XJ or a V-6, disregard the following and go to 4.88's for any tire size larger than 30". So general gearing guide from your friends at URF:

30', 31's: 4.10 (don't do something stupid like I did and go to 3.73. Fully homosexual, but hey I was a freshman in college at the time.)

32's, 33's: 4.56 (If you live in the mountains, or your rig is on a trailer a lot, pull the string out and go to 4.88's)

35's: 4.88's (Only because you can't get 5.13's in a Dana 30. If you live in a state that has a SINGLE rock you may one day want to climb, ditch the 30 and step up to a 44 and 5.13's)

37's: 5.38's will do you nicely, but your still going to want deep T-case gears.

For those with short attention spans. HTH.

 

[themangeraaad]

Ok, first off, I know there are plenty of posts just recently about 30-33 in tires on a 4.0 with the manual tranny and what gears to use.. but I was lookin for specific advice on my Jeep... I am getting 32x11.50 SSRs soon, and its a question of swapping in 4.10s or 4.56s. I understand the arguments for both, but which would y'all recomend? Im thinking 4.56 because of the width of the tire on top of any other drag increasing mods, so thats my belief, but right now, other than lift and tires, im stock, so there isnt much more going on yet, and there might not be for quite some time. I have 30" tires on the stock 3.07 which dropped my mpg to about 15 (not sure what it was before, but last several tanks i tested I was at 15ish combined city and highway) I do quite a bit of driving to and from school (a 2 hour drive) so economy is important... which has the better chance for better economy? the 4.10s or 4.56s? Sorry for another somewhat repetitive question, I just want the security of having at least someone elses opinion on it, then if it sucks, i can put the blame off on others ^_^

 

[Kejtar]

Ok, first off, I know there are plenty of posts just recently about 30-33 in tires on a 4.0 with the manual tranny and what gears to use.. but I was lookin for specific advice on my Jeep... I am getting 32x11.50 SSRs soon, and its a question of swapping in 4.10s or 4.56s. I understand the arguments for both, but which would y'all recomend? Im thinking 4.56 because of the width of the tire on top of any other drag increasing mods, so thats my belief, but right now, other than lift and tires, im stock, so there isnt much more going on yet, and there might not be for quite some time. I have 30" tires on the stock 3.07 which dropped my mpg to about 15 (not sure what it was before, but last several tanks i tested I was at 15ish combined city and highway) I do quite a bit of driving to and from school (a 2 hour drive) so economy is important... which has the better chance for better economy? the 4.10s or 4.56s? Sorry for another somewhat repetitive question, I just want the security of having at least someone elses opinion on it, then if it sucks, i can put the blame off on others ^_^

Better economy? Don't do anything: keep same tires, same gears.
What to do? Consider 4.56 or 4.88.

 

[Gojeep]

Ok, first off, I know there are plenty of posts just recently about 30-33 in tires on a 4.0 with the manual tranny and what gears to use.. but I was lookin for specific advice on my Jeep... I am getting 32x11.50 SSRs soon, and its a question of swapping in 4.10s or 4.56s. I understand the arguments for both, but which would y'all recomend? Im thinking 4.56 because of the width of the tire on top of any other drag increasing mods, so thats my belief, but right now, other than lift and tires, im stock, so there isnt much more going on yet, and there might not be for quite some time. I have 30" tires on the stock 3.07 which dropped my mpg to about 15 (not sure what it was before, but last several tanks i tested I was at 15ish combined city and highway) I do quite a bit of driving to and from school (a 2 hour drive) so economy is important... which has the better chance for better economy? the 4.10s or 4.56s? Sorry for another somewhat repetitive question, I just want the security of having at least someone elses opinion on it, then if it sucks, i can put the blame off on others ^_^

Been running 31's and 4.11's for years and just went up to 32's and hate the gearing now. Next week I am fitting 4.56's so would advise the same as the power loss and engine strain increased the fuel use around town and made my engine and auto run hotter due to slower speed of the water pump.

 

[Kilted XJer]

Running 31's on stock gearing with a non HO 4.0 and auto tranny. I have 2 sets of tires (all terrains for daily driving, trxus mt for off road) both are 31s. I've made room for 32s or even 33s but I am going to keep the 31 all terrains for daily driving. Now I'm going to re-gear and add lockers. I need to make a decision that will best fit both my tire sizes (it seems 32s would be more likely). I'm thinking 4.10 because most of my driving is in the city. How bad will it be off road? Keep in mind that I'm probably used to an underpowered setup in my current situation (31s on stock gears).

 

[Lincoln]

Running 31's on stock gearing with a non HO 4.0 and auto tranny. I have 2 sets of tires (all terrains for daily driving, trxus mt for off road) both are 31s. I've made room for 32s or even 33s but I am going to keep the 31 all terrains for daily driving. Now I'm going to re-gear and add lockers. I need to make a decision that will best fit both my tire sizes (it seems 32s would be more likely). I'm thinking 4.10 because most of my driving is in the city. How bad will it be off road? Keep in mind that I'm probably used to an underpowered setup in my current situation (31s on stock gears).

If the tranny is the '88 in your profile I would go with at least 4.56's. 4.10's with 32's suck donkey balls. I ran 5.38's with 35's for a little over a year and I was more happy with that setup than any I've run. With 4.88's and 31's you would still be under the 3K mark (2980@80mph). If you plan on running rocks do the 4.88's, if your just doing general wheeling the 4.56's would work. If you only go up to 32's I wouldn't bother with two sets of tires.

 

[Kilted XJer]

I do 95% of my driving on road. I already read that 4.56 and 31s suck for gas mileage. How bad will it be? It's not good right now. I don't even get 15mpg on a good tank.

 

[Gojeep]

I do 95% of my driving on road. I already read that 4.56 and 31s suck for gas mileage. How bad will it be? It's not good right now. I don't even get 15mpg on a good tank.

Funny thing is that I know guys that get better mileage with 4.56's than 4.11's on 31's?
Think it might depend on what speed you like to cruise at but below 70 mpg I would go the 4.56's. My mileage got worse with my 4.11's and 32's compared to 31's so why I fitting 4.56's.

 

[Semper Fi]

I have been reading all the posts I can find about gearing because I'm going to re-gear and lift my Cherokee with an RE 4.5 inch lift. I have a rough country 3 inch on it now (go easy on me for that one, it was cheep) and I'm running 255/70/16's on it and I'm told they are about as big as 32's. It has the stock 3:55's in it and it runs just fine. I use it for a DD and some offroad during the summer. I have very little to complain about. It does just fine offroad and on road it has plenty of power. It isn't going to win many drag races, but it is slow either. As far as MPH I get about 16 MPH and when I drive from PA to AR I get about 21. I uderstand that most off you guys like the 4:56 gears but I think most of you that say that, are doing more offroading then some of these guys. I think I'm going to run the 4:10's in mine with the 32's I plan to put on it. I know a lot of you may disagree with me, but all of the 4x4 shops I have been to have told me the same thing. If any of you guys get the Quadratec catalog for Wranglers turn to page 143 (in the newest catalog with the red Wrangler on the front) and look in the upper left corner and there is a caculator there that says with 4:11's and 32's that you will be turning 2,800 rpms. A lot of you say to stay at 3000 rpms, I think that is close and my gas mileage and power will be just fine with the 4:11's and 32's
Just my opinion, what do you think?

 

[Lincoln]

I do 95% of my driving on road. I already read that 4.56 and 31s suck for gas mileage. How bad will it be? It's not good right now. I don't even get 15mpg on a good tank.

It really depends on the overdrive ratio. Most of the Renix XJ's had a .705 ratio in the auto. I went from 4.10's and 33's averaging 15 mpg to 5.38's and 35's and averaged 17-18 mpg. Mines not a daily driver anymore so it gets road miles for hunting and to the trail.

If you think it revs too much just leave the 32's on it.

 

[Lincoln]

I have been reading all the posts I can find about gearing because I'm going to re-gear and lift my Cherokee with an RE 4.5 inch lift. I have a rough country 3 inch on it now (go easy on me for that one, it was cheep) and I'm running 255/70/16's on it and I'm told they are about as big as 32's. It has the stock 3:55's in it and it runs just fine. I use it for a DD and some offroad during the summer. I have very little to complain about. It does just fine offroad and on road it has plenty of power. It isn't going to win many drag races, but it is slow either. As far as MPH I get about 16 MPH and when I drive from PA to AR I get about 21. I uderstand that most off you guys like the 4:56 gears but I think most of you that say that, are doing more offroading then some of these guys. I think I'm going to run the 4:10's in mine with the 32's I plan to put on it. I know a lot of you may disagree with me, but all of the 4x4 shops I have been to have told me the same thing. If any of you guys get the Quadratec catalog for Wranglers turn to page 143 (in the newest catalog with the red Wrangler on the front) and look in the upper left corner and there is a caculator there that says with 4:11's and 32's that you will be turning 2,800 rpms. A lot of you say to stay at 3000 rpms, I think that is close and my gas mileage and power will be just fine with the 4:11's and 32's
Just my opinion, what do you think?

I'll try and pick up all the issues:

1. 255/70-16's have a caculated height of 30.5". Closer to a 31.

2. Most people are happy with their gearing until they try something better. Satisfaction can also be skewed by more flat land than mountains or hills.

3. Very few Off Road shops have given me good advice on gears.

4. I don't have the catalog but I bet that calculator is based on a 65 mph speed and no overdrive (1:1 drive ratio). I don't know the specs on your XJ and since there are several OD ratios out there we'll use the Renix XJ with an auto for an example. With 32's, 4.10's, .705 OD ratio you would be turning roughly 2430 at 80 mph. Say you had one of the manuals with the .75 OD it would up that to 2583 and I believe there was even a ratio around .80:1 which would leave it at 2755. On the street each would feel slightly different.

I don't know many people that were happy with 4.10's and 32's on the trail. The ones that claimed they were happy completely changed their minds after driving something better.

 

[Gojeep]

255/70/16 are even less than 30.5"
70% of 255 = 178.5 mm of one sidewall height.
x 2 ( for both sidewalls ) = 357 mm or 14.05"
+ the wheel rim size of 16" still only gets you 30.05"

No wonder he thinks the gearing is fine as not much over stock!

 

[Lincoln]

255/70/16 are even less than 30.5"
70% of 255 = 178.5 mm of one sidewall height.
x 2 ( for both sidewalls ) = 357 mm or 14.05"
+ the wheel rim size of 16" still only gets you 30.05"

No wonder he thinks the gearing is fine as not much over stock!

Oops, I fat fingered that one.

 

[Semper Fi]

I have a 2001 with the auto trans with 3:55's, and 4.0L. and I'm sure that my tires are bigger than the stock ones that I took off. The 255/70/16's that I put on it are the same size as the tires that Jeep is putting on the new Wranglers which they claim are 32's. So I think either Jeep or you guys are doing the math just a little off, you guys tell me. I bet they are closer to 31's but the same size as the 30's that I took off, I think not. As far as the Jeep being used on flat land, well have you ever been to Pennsylvania? We have a boat load of mountains around here and I can see them out of every window in my house. I'm not saying that 4:56's aren't the best choice for power, I'm sure they are. What I'm getting at is that most of you run your Cherokee's off road more than on road. There are a couple of us that use our Cherokee's on road more than off, and are looking to have better MPG's then we are power off road. If you can tell me that 4:56's are going to give me the better MPG's and power with 32's then the 4:10's and 32's then that is what I will run. But you guys have to understand that your telling me one thing and the shops are telling me another. I would like to run 33's but don't want to cut on the Cherokee and have to have the tires covered to be legal. So I will be sticking with the 32's for not only that reason but if I go higher it's not a good DD anymore and it gets a lot more expensive after the 4.5 inch lift. So yes I have lots of hills around here, yes I do run it off road ( I'm going tomorrow with 2 Wranglers and want to spank their ass in the Cherokee), and yes I'm looking for the best on road MPG's and off road compromise. Thanks for the help.

 

[Lincoln]

I have a 2001 with the auto trans with 3:55's, and 4.0L. and I'm sure that my tires are bigger than the stock ones that I took off. The 255/70/16's that I put on it are the same size as the tires that Jeep is putting on the new Wranglers which they claim are 32's. So I think either Jeep or you guys are doing the math just a little off, you guys tell me. I bet they are closer to 31's but the same size as the 30's that I took off, I think not. As far as the Jeep being used on flat land, well have you ever been to Pennsylvania? We have a boat load of mountains around here and I can see them out of every window in my house. I'm not saying that 4:56's aren't the best choice for power, I'm sure they are. What I'm getting at is that most of you run your Cherokee's off road more than on road. There are a couple of us that use our Cherokee's on road more than off, and are looking to have better MPG's then we are power off road. If you can tell me that 4:56's are going to give me the better MPG's and power with 32's then the 4:10's and 32's then that is what I will run. But you guys have to understand that your telling me one thing and the shops are telling me another. I would like to run 33's but don't want to cut on the Cherokee and have to have the tires covered to be legal. So I will be sticking with the 32's for not only that reason but if I go higher it's not a good DD anymore and it gets a lot more expensive after the 4.5 inch lift. So yes I have lots of hills around here, yes I do run it off road ( I'm going tomorrow with 2 Wranglers and want to spank their ass in the Cherokee), and yes I'm looking for the best on road MPG's and off road compromise. Thanks for the help.

Review GoJeep's calc for tire height. There are 25.4 mm to 1". I don't know a lot of details about the new Cherokee's but I believe they came stock with 225/75-15 (28.3") or maybe a 225/70-16 (28.4"). Your larger than stock but definately not a 32" tire. Go to a tire shop and roll a 32 up next to yours.

The 2001's with the auto had a .75:1 OD ratio. With 4.56's and real 32's you would be about 2900 rpms at 80 mph. I would consider that the high end of the range for for daily. You probably would be happier with 4.10's unless you plan on doing any crawling in the rocks. If you have the desire to do that go with 4.56's. If you don't run 80 a lot down the freeway I would still get the 4.56's.

For comparison XJNana would be turning 2700 rpm's with those same 32's. That would be right in the sweat spot.

 

[WB9YZU]

Jeep Cherokees came with an assortment of tire options. See BFG tire selector for your year/model, but I believe an accurate general statement would be that they came with 215X75X15 through 225X70X16, in otherwords, depending on brand and tread type, somewhere between a 27.5 and 28.3" tire. round that off and you have 28".

The premise of this thread is that CRASH is tired of gearing questions. Thus he generates a very short list and posts it as gods word. Someone else suggested making it a sticky; How foolish. Since gear selection depends on a selection of trade offs; Auto VS Manual, milage VS power, Crawl ratio VS roadability. Because of that there can be no standardized list, only a range with the options. What is totally unacceptable to some, a 3.55 ratio, automatic, 4.0L, and 31's, works fine for others because it's good on fuel (something a lot of folks are looking at nowdays).

What would be more reasonable is an article on the subject.

 

[woody]

Ahh but there is a LOT of anectedotal evidence that points towards lower -higher numerically- gearing improving MPGs (at all but extremely high road speeds) possibly because it gets the 4.0 up into a more efficient RPM zone. I don't know why for certain, but I do know it was the case on both my MJ 5speed and my XJ AW4... tires being the same, 3.xx to 4.56 improved both the driveability and fuel efficiency. The XJ automatic saw a further improvement in MPG and 'fun' going from "33s" to "31s" with the 4.56:1.

You are correct that there is not a one-size-fits-all approach and there will; be trade-offs with whatever ratio one picks, but since there are only five gear ratio choices (for the HP30 - 3.07, 3.55, 3.73, 4.10, 4.56, 4.88) and four (for the 8.25 - 3.07, 3.55, 3.73, 4.10, 4.56) it's easier to speak in general terms.

It's also easy to fall into the "diameter trap" ASSuming that your 31"s or whatever are actually the dia. as stated. More accurate predictions can be had by using the working radius x 2 (the actual measurement from the hub center down to the driving surface x 2 as a 'diameter')