Considering Changes... Dana 44 front, 4.10 gears...

[Mudderoy]

Recently I have been monitoring the instant MPG and average MPG via my OBD II scanner.

Great information (if correct). I noticed that driving down the highway at 75 mph I was getting an instant MPG of 13. I don't do much highway driving so I need to do more and see exactly where the "sweet" MPG MPH is. I suspect it's around 55 mph and 2200 rpm (About 18 to 19 MPG according to the scanner).

I love the 4.56 gear but with 32" tires it is over geared for the highway. Fun off road. Really never have to press on the gas petal to get up and over large obstacles. But I have a daily driver.

So I have been mulling over installing a rear locker, which will require the ring and pinion to be set up again. For a couple of hundred I could get 4.10 gears. Of course that would mean I either lock and re-gear the front at the same time. That was the long term goal.

Also it's time to buy tires, and I was going to go from 32 to 33" which will help with the highway rpms but I don't think enough to help with the mpg.

Going the path of least resistance I'm going to get the tires first and see what that does to the rpms on the highway.

One other option would be to replace the axles. Dana 44 front and 8.8, or 9" in the rear. Then lock and re-gear to 4.10. Of course with those axles I could run 35" tires locked so 4.56 would be the way to go.

Another option would be to go to 35" tires, lock the rear and leave the Dana 30 open. That would bring my rpms down on the highway to near stock and the 29 spline 8.25 rear should be ok with the 35's locked (if I am remembering correctly)

It would mean that I need to SYE and replace the 4.5" coils with 6.5" coils before putting the 35's on.

My NP242 chain is stretched so I'll be replacing the chain, the drive and driven gears and I'll do the SYE at the same time. The 35's might fit on it now since I have the bushwackers, just have to measure.

So what do you think?

[Mudderoy]

Tire Description |Max Load| Max. Inflation Press.| Tread Depth| Tire Weight| Rim Width Range Meas. |Rim Width |Sect. Width |Tread Width | Overall Diam.| Revs Per Mile| Country of Origin*
BFG MT KM2 35x12.5x15 |2535 lbs. |35 psi |20/32" |61 lbs. |8.5-11" |10" |12.5" |9.4" |34.8" |598 |US
BFG MT KM2 32x11.5x15 |2535 lbs. |50 psi |20/32" |52 lbs. |8-10" |9" |11.4" |8.7" |31.8" |654 |US

So the 35's are 3" wider in diameter than the 32's. That means I need an additional 1.5" of space between the fenders and the 32's (when they were new!) lol

||3.31|3.42|3.55|3.73|3.91|4.11|4.27|4.56|4.88|5.1 3|5.29|5.38|5.71|6.17|7.17
|32"| 2259| 2334| 2423| 2546| 2696| 2805| 2914| 3112| 3331| 3501| 3610| 3672| 3897| 4211| 4894
|35"| 2065| 2134| 2215| 2328| 2440| 2565| 2664| 2845| 3045| 3201| 3301| 3357| 3563| 3850| 4474


This table is a little misleading in as much as the rpms are higher that in real life. It is based on a speed of 65 mph and a manual transmission. Not an automatic with over drive.

The rpm difference on the chart between the 32 and 35" tires is 267 rpm. So applying that same difference to my specific equipment I should expect to see...

Tire Size|Speed MPH|RPM
32"|80|3,000
|70|2,800
35"|80|2,733
|70|2,533

[4.3LXJ]

Wow Tony, lots of options thee. It is true you are geared for 35s right now. But I would doubt you would see any significant change in milage, in fact you might decrease it with the larger tires. They are an inch wider and heavier etc. Mud treads also are famous for decreasing milage one or two miles per gallon. as far as the locker goes, I put in an Aussie locker for our last little romp and certainly cannot complain. The big advantage there is that you don't have to reset the gears. I think for your use, it is plenty strong enough. After the way I treated it, I am a believer. The thing is on a gear swap with locker, how long do you drive it before you break even on the swap. Also, bushwackers have been advertised to clear 35s. Might have to bump stop some more or go a little higher.

[bluedragon436]

If it were me.. I would do the Aussie locker, that way you don't have to pay someone to reset the gears.. swap out your 242 chain & install the SYE.. then go with the higher lift springs, and the larger tires... but that is just because that was my eventual goal, and I know you wouldn't mind having a higher beefier looking XJ!!

[Mudderoy]

I found this on another site...

This pisses me off! lol


regearing is the best money ive ever spent on the Heep
98' auto on 32's w 4.56's i get around 17 mpg in town and about 20 to 24 mpg highway as long as im not going 75....
at 65 in OD i sit at about 2750 RPM
at 75 in OD i sit at 3100 RPM
but have power to spare going up hills
being loaded up for a weeks camping (750lbs, probably more) and passing cars going up the pass is nice.

:link: (http://www.cherokeeforum.com/f2/what-gears-do-you-run-33in-tires-51774/)

[Mudderoy]

Logically 33" tires are the way to go. 35's will look cool but can add a host of problems actually taking the Jeep off road.

Really the only reason I am considering the 35's now is to drop the rpms down on the highway.

Most people are not running 35's and 4.56 gears. I've done a little searching and found the link I just posted above.

I'd like to get some first hand information from people running 35" tires. Especially with 4.56 gears.

So if you have this experience please share here with us your mpg, and anything else you can think of that would be of value to someone thinking about going the 35" tire route.

:thanx:

[LizardRunner]

Can't help you Tony, I am running 3.73's and 30's. I do know that running 35's you need more than 5" lift for tire clearance.

[Paddletrucker]

Those charts with the RPM's always seem off to me. I've got a 5-speed and I can't see running the RPM's that high. On all stock everything, I do about 2,000 at 65. At 3,000 it sounds like it's winding WAY too high.

I copied this from NAXJA. Don't know if you've seen it before or if it helps at all, but I find it interesting to compare the the chart you posted.

Last weekend, I was going up a huge, steep hill out in the country and decided to see just how far I could lug it down and see how it'd still pull. I was very surprised to feel how much power I still had barely creeping in 4th gear. I could still accelerate, although slowly. I was right around 1,000 RPM's. I think I'd like to re-gear one of these days. According to this below, I'd need to go from 3.07 to 3.55 to run 31's. I was thinking 3.73's. Everybody tells me, "No, you want 4.10's" Oh, brother.



"Deciding what gear ratio to use when changing tire size is actually quite simple.
It's just a matter of mathematics.

Current tire size/new tire size =current gear ratio/new gear ratio

This simple formula will allow you to figure out what ratio will get you back to your current performance.
For instance, let's say you have stock 3.55 gears & stock tires and want to go to 33" tires.
Stock XJ tires are about 27" tall so:

27/33 = 3.55/new gear ratio

Cross multiplying (thought you'd never use algebra again?) gets you this:
33 X 3.55 = 27 X new gear ratio

117.15 = 27 X new gear ratio

117.15/27 = 4.34

IOW, 4.56 gears (the closest avail to 4.34) will give you slightly lower gearing than you had while stock.
From here it's up to you where to go.
If stock performance is fine stay with 4.56. If you want a little more low end grunt, go to 4.88. If you want to murder the rocks go to 5.13 or lower.
BTW, lower gears = higher numerically."

[Paddletrucker]

I wonder if that RPM chart is at 65 running in 4th gear??

[Mudderoy]

I wonder if that RPM chart is at 65 running in 4th gear??

Yes it is. Well 65 mph manual transmission and 1:1 ratio. So I believe that would be 4th gear.

I checked mine today and I do 2200 rpm at 60 mph.

[4.3LXJ]

Nate, the rpm difference is due to the difference in ratios in overdrive. Yours is only 14% I believe. The AW4 has something around 25% IIRC

[Paddletrucker]

Ok thanks. Maybe I would like 4.10's then.

[bluedragon436]

Yeah I was going to go with 4.56's on my 33's... but was told unless I was really planning on hitting 35's with my axles.. to go with 4.10's... I don't see myself going any taller than 33's with my XJ... at least not on stock axles anyways.. or while it is my only DD!!

[Paddletrucker]

My plan is sorta screwy. For reasons that don't have anything to do with my Jeep, I chose to go with the 3" from ROugh Country with the upgraded X-Flex control arms. For now, I'll run 31 X 10.50's on it. I really don't want to go the full 4.5, but I do want to be a little taller than 3". I know that sounds nuts, but I do have a good reason.

So, my plan is to go up a little next summer with the shackle relocation brackets and a small change on the front. Then, I'll probably go to 32 x 11.50's. I really don't see going bigger than the 32's for what I want to do.

That leaves me in somewhat of a dilemma. Do I gear for the 31's or the 32's? Gear for off road, daily driving, or towing (I do lots of that)? Is there a compromise? What about axle upgrades? I plan to keep the XJ and one day get rid of the D-35, and maybe the D-30. Should I wait? Oh, crap! What about my plan for lockers? I know I want to re-gear, I'm just not too sure what configuration I want to re gear for. I have a guy who'll do it for me for nothing if I can find the parts, so maybe I'll do it twice a few years apart. I've spent more on stupider things. Who knows what I might do.

I've come to the conclusion that this whole Jeep thing was an elaborate plot by the Germans and Daimler Chrysler to distract me and keep me from taking over the free world!!!

[Mudderoy]

I think what I'll do is go with the 33's and then work towards a Dana 44 front end. Once I have that locked 35's front and rear should be a doable.

My mpg issue probably isn't an rpm issue. I need to change out the fuel pump and regulator. I know the regulator has an issue.

[4.3LXJ]

My plan is sorta screwy. For reasons that don't have anything to do with my Jeep, I chose to go with the 3" from ROugh Country with the upgraded X-Flex control arms. For now, I'll run 31 X 10.50's on it. I really don't want to go the full 4.5, but I do want to be a little taller than 3". I know that sounds nuts, but I do have a good reason.

So, my plan is to go up a little next summer with the shackle relocation brackets and a small change on the front. Then, I'll probably go to 32 x 11.50's. I really don't see going bigger than the 32's for what I want to do.

That leaves me in somewhat of a dilemma. Do I gear for the 31's or the 32's? Gear for off road, daily driving, or towing (I do lots of that)? Is there a compromise? What about axle upgrades? I plan to keep the XJ and one day get rid of the D-35, and maybe the D-30. Should I wait? Oh, crap! What about my plan for lockers? I know I want to re-gear, I'm just not too sure what configuration I want to re gear for. I have a guy who'll do it for me for nothing if I can find the parts, so maybe I'll do it twice a few years apart. I've spent more on stupider things. Who knows what I might do.

I've come to the conclusion that this whole Jeep thing was an elaborate plot by the Germans and Daimler Chrysler to distract me and keep me from taking over the free world!!!

OK, Jeep bug has bit and pumping more venom into you. It has you in upgrade delirium, curable only with lots of dollars and time with a wrench in hand. There is no known vaccine, only spousal abuse will prevent you from succumbing for a short time.:p

This is a problem that hits us all one time or another. Which way do I go? What am I going to do in the future? So, one question is: what is the total lift you will attain when done?, total tire size when done? etc. So now once you have the maximum numbers, then you build for that. I have been doing that since I started my build five years ago. Slow I know, but sure I guess.

So you will have what? 4" lift and 32s? And what rear will you have when done?

One thing I would point out on the upgrade is that 4.10s came standard on 4 & V6 Jeeps. That makes the 4.1 D30 a cheap option from a wrecking yard. Front ends generally have little gear wear. Just change seals, ball joints and wheel bearings and you have a fresh front end. Might have some luck and find a later 8.25 with the 4.10s too, or use a Ford 8.8". That makes your gear change much cheaper and easier with that swap. So you could be looking at what you want to do with gears and a locker and stronger rear at $600 tops.

[Paddletrucker]

Yeah, building toward what I want to end up with is what I'm trying to do.

I'm pretty sure I want to end up around 4 inches. Maybe a smidgeon more. Not right now, though. I'm using the top of my Jeep for kayak hauling I'm thinking 3" will be plenty high enough to lift my 16' long 65 pound boat. I have one barn door I need to drive in and out of this next winter and a 4.5" lift would screw that up.

Thanks for letting me know about the Dana 30 4.10 ratio from another Jeep! I had originally decided to just bite the bullet and do Dana 44's front and rear, but that's expensive. Then again, I have no plans of getting rid of the Jeep, so all these things I'm spending money on is long term.

This Jeep stuff is almost as bad as airplanes. I would have never thought that would be the case at all. My wife likes it, though. My XJ Cherokee is one hell of a lot cheaper than a Piper Cherokee!!:D

http://i275.photobucket.com/albums/jj298/picsofnate/N9280A.jpg

[bluedragon436]

I wish I could find a Ford 8.8 for $600.. they wrecking yards around me want way too much for all of their parts.. especially axles.. was trying to pick up a D35, so I could pull the brake parts off for a disc swap on my 8.25.. but they wanted almost $500 for the axle.. I was like the hell with that..

[bigjim350]

Can get 8.8's all day long around here for 200 or less. been eyeballing my explorer lately. it has a 4.10 8.8 with disc and lsd. hmmm wonder if there is a write up for putting a 8.25 in a explorer...

[jeepxj95]

i think 4.10's will be fine for u. maybe a little high for a DD but then u said u tow with it so... i think u'll be happy with that. if it was just a DD then i would say 3.73's. wish i could get 3.73 for the 8.25 but oh well.

[4.3LXJ]

I wish I could find a Ford 8.8 for $600.. they wrecking yards around me want way too much for all of their parts.. especially axles.. was trying to pick up a D35, so I could pull the brake parts off for a disc swap on my 8.25.. but they wanted almost $500 for the axle.. I was like the hell with that..

Man, you could almost by a whole XJ for that:out:

[bluedragon436]

Man, you could almost by a whole XJ for that:out:

Not around here you won't... around here even older XJ's are expensive.. everything up here is selling like it is limited edition or something anywhere else.. Hell when I bought my XJ they wanted 6k for it.. I laughed at the guy, said all the listings you guys use to price values show this thing being worth high 4k, low 5k depending on the shape of it.. I told them I had $4,500 cash I would give him, and he takes care of all the charges to get it registered.. ended up walking away with it for $4k.. but I am constantly amazed at how much they charge for vehicles around my area.. think I am going to continue looking for the truck I want down in SC area where I'm from.. way more reasonable pricing.. would be even better prices around TX on a truck too..

But I think a little bit later I might look for a D30 out of an XJ with 4.10's factory, and rebuild it put a selectable locker in it.. then pick up a 4.10 gear set for my 8.25.. that way I'll only have to pay to have one gearset installed.. cause that is another things that is hellaciously expensive up in DE/MD getting stuff like that done, cause there aren't a whole lot of shops that do it..

[4.3LXJ]

too bad man. Here I can pull a rear for $200 and front for $300

[Leonmac]

Hey guys,This is my 2 cents worth. When looking for the best performance/economy first you need to know where the peck of the engines touque is, generaly that is as close to the sweet spot for touring as you will get, over that and you are tending to rev too high for mph and below tending to lug a little and having to press alittle harder on the gas when starting to climb hills. I don't know enough about the 4.0L engine to say where that is. Also a big factor in fuel economy is the terrain you travel most in. You guys in The US have alot of flat highways with long gradiants and long flowing corners. Here in NZ we have steep gradiants and sharp corners and Lots of them, I find the stock gearing in my jeep a bit high for where I travel and it is forever changing gears. So I would select a Ratio lower than you would and prob still get similar perfomance for the conditions, Just my opinion, GO BIG, TO HELL with Mpg LOL cheers Leon.

[XJ Rat]

I found this on another site...

This pisses me off! lol



:link: (http://www.cherokeeforum.com/f2/what-gears-do-you-run-33in-tires-51774/)

Tony;
I call that link BS. Remember, anything can be posted on the internet. He probably forgot to change the spedo gear in his transfer case, and that is how he is now getting that miraculous gas mileage. Lift = worse mileage. Larger tires = worse mileage. Sure changing gears will help, but not give the mileage increases he is claiming! I had 4:10 gears in my TJ (AX15 5-speed manual) using the same 32" Swampers you saw on my XJ. I once got 17.2 mpg with it, I was tickled pink with that. Before the 32" Swampers I was running 31" AT with the 4:10 gears. 2nd gear starts were no problem. One time, and only one time, I got 22 mpg with it. That was 100% freeway driving with the hardtop on, doors on, and using about 1/2 tank of gas (It was the last leg from Washington DC to my home in PA). With the 31's I was getting between 16 and 17 normal driving. Sometimes as low as 13mpg.

[4.3LXJ]

Just to really make you POed, there is a gal on Yahoo groups with a stock XJ consistently claiming 28 mpg. But she claims she drives 55 mph on flat ground only with the cruise on and no AC.muahaha

[Mudderoy]

Just to really make you POed, there is a gal on Yahoo groups with a stock XJ consistently claiming 28 mpg. But she claims she drives 55 mph on flat ground only with the cruise on and no AC.muahaha

:wow:

[XJ Rat]

Just to really make you POed, there is a gal on Yahoo groups with a stock XJ consistently claiming 28 mpg. But she claims she drives 55 mph on flat ground only with the cruise on and no AC.muahaha

Downhill with a good back wind. No A/C because the engine is off. :D

[BlueXJ]

I have never seen that type of mileage on an XJ and I have been messing with them since 1987.

[2K1XJ]

For what its worth...I run 4:10s with 32s on my 2001 XJ Auto trans...it does great off road and seems to be as close to stock as possible on the freeway...my next tire change will be 33s and I think it will do just fine. I get crappy mileage regardless.

[Mudderoy]

For what its worth...I run 4:10s with 32s on my 2001 XJ Auto trans...it does great off road and seems to be as close to stock as possible on the freeway...my next tire change will be 33s and I think it will do just fine. I get crappy mileage regardless.

lol thanks. Yeah it's like I've said a few times (perhaps not on this post) I was perfectly fine with the concept of bad a$$ off road rig = bad gas mileage. But NOOOO I see these people talking about 16 and 17 mpg on the highway running the same setup and me.... I just don't want to throw away money because I was too apathetic to research a solution.

[jeepxj95]

For what its worth...I run 4:10s with 32s on my 2001 XJ Auto trans...it does great off road and seems to be as close to stock as possible on the freeway...my next tire change will be 33s and I think it will do just fine. I get crappy mileage regardless.

how crappy is crappy? is it below 16?

[2K1XJ]

I haven't put in a new speedo gear...however, I did calculate the correct variance and I use that to figure MPG. In other words, I zero speedo and mileage on GPS, then I drove a known distance and compared the two numbers...based on these numbers, I can figure the variance and get a SEMI-accurate mpg figure.

Anyway, I regularly get 12-13 mpg around town and 14-15 mg highway.

[ageent.007]

I'm actually getting about 30mpg in my 95 with a 6" lift on 35" bfg mud terrains......now diesel fuel is a little more expensive but I'm happy Haha

[bluedragon436]

Yeah I wish I could get 20mpg, much less 30.. I would love to upgrade my 4.0 to a turbo diesel.. that would def. be way nice torque for wheeling and help in the MPG... Maybe one day, I'll learn to fab.. then I could make that happen!!

[ageent.007]

Yeah definitely with some solid Fab skills its definitely doable. Definitely need the right gearing though, mine red lines at 3k.

[jeepxj95]

I haven't put in a new speedo gear...however, I did calculate the correct variance and I use that to figure MPG. In other words, I zero speedo and mileage on GPS, then I drove a known distance and compared the two numbers...based on these numbers, I can figure the variance and get a SEMI-accurate mpg figure.

Anyway, I regularly get 12-13 mpg around town and 14-15 mg highway.

i did something like that. but i used my grandmas saturn. for the known disence. then i had to find out the difference between the two. ex jeep miles divided by .8 = actual miles 230 divided .8 = 287 divided by 16 gallons = 17.96 mpg. 31's with 3.55 = 17-18 city and around 20-21 highway

[Mudderoy]

I'm actually getting about 30mpg in my 95 with a 6" lift on 35" bfg mud terrains......now diesel fuel is a little more expensive but I'm happy Haha

Works out cheaper though doesn't it?