4.56 on 31's

[OutkastBoss]

I got no #'s for ya but here are some opinions about my experience running 4.56 gears with 31" tires on my auto XJ for a few years before stepping up to 33's.

Stock gears and 31's wasn't bad but it did feel a bit underpowered and 4low was used TONS.

My 4.56 gears and 31's were fine for years of Daily driver duties and great with the trailer. I don't usually go more than 5 over but it could handle 10-15 over pretty well on the highway on long trips. In busy traffic it jumped out and took off from a stop VERY quickly. We have lots of stop signs at the bottom of steep hills here, I loved how I would down shift and people think my brakes are out until I am at the stop sign easing to a stop.We towed it over a steep mountain pass in co and even towed 1,000 miles to Moab and wheeled with and without the trailer with that setup. For the years we ran this setup we only used 4low on a couple of spots and almost exclusively with the trailer. when we used it it wouldn't be for long because we couldn't keep up with the group who was in 4low.

It drives better all around now that I have 33's and handles the highway better. I feel like it is still a bit lower than it was stock and still have some of positives of being a little lower geared but not to the exaggerated extent where it causes all the negative effects on road driveability or making 4low virtually unecessary. It does not feel underpowered like it did with the stock gearing and 31's.

We towed the trailer to Winterfest after the 33's and it did great and wheeled up some pretty crazy stuff and it still had the pull needed for the trailer. 4low is back in regular rotation and is way more useable. Then we towed it to and from Harlan and the hills around the black mountains made me miss the extra oomph I had with the 31's but it did the job.

What mileage did I or do I now get? Hell idk its probably not super great being a lifted shoebox covered in steel parts/bumpers/etc. If I did not wheel anything harder than hunting trails I would run 31's and it would be a tough call as 4.10's would be great for around here and even in the Ozark "mtns" it would be fine and have better all around driveability. However when I visit my parents in Co there is plenty of long inclines some of which are VERY steep. (which reminds me add a trans cooler to your rig). If I lived there I would do 4.56's and 31's on a hunting rig.

for a hunting rig that makes I would lean to 4.10 for my area and use. If you go up in tire size later you will regret 4.10's though so keep that in mind and build it to suit your needs/terrain!

 

[sunburned]

I had 4.56 gears and 32's for a few years. I probably put 40k miles on it during that time, lots of highway miles cruising at 75-80. No issues.

I'd definitely recommend the 4.56s. Never had 4.10s, but I'd always err on a slightly higher gear than a lower one.


Besides, you'll go bigger eventually I said I'd never go over 32's, no reason to. Ran 32s on a 4.5" lift for a while, then boom, had 35s.

 

[MoparManiac]

That said, on our EFI 4.0 jeeps, fuel use is directly related to throttle position and MAP - RPM's are not a primary factor in fuel load.

I would think most MAP-driven EFI systems calculate required fuel by engine speed x Vacuum (RPM/kPa)...so nothing to do with throttle position unless you go to an alpha-N setup. At least, this is how my Megasquirt system does it and it makes the most sense to me.

I can certainly see how a higher RPM with less load COULD result in less overall fuel usage, but that really is dependent on the tune being used. If the engine is in a lighter load scenario, you don't necessarily HAVE to keep a 14.7 mixture. You can dip into the 15s, 16s, and sometimes 17s in order to build efficiency. If you're under a higher load, you usually start climbing to the low 13, high 12 mixture in order to keep the motor running at those lower RPMs.

Now you also have to introduce the speed of the motor. Let's say you're churning 2200 RPMs at something like 70-80 kPa, or with deeper gears it would be 2800 RPMs at something like 40-50 kPa. Sure the higher RPM would be demanding less fuel, but certainly more injection events.

Like I said, it really depends on the tune that the OEM used at the time, and a lot of other variables that are vehicle specific. I don't think there's really a definite answer here.

 

[cal]

I would think most MAP-driven EFI systems calculate required fuel by engine speed x Vacuum (RPM/kPa)...so nothing to do with throttle position unless you go to an alpha-N setup. At least, this is how my Megasquirt system does it and it makes the most sense to me.

I can certainly see how a higher RPM with less load COULD result in less overall fuel usage, but that really is dependent on the tune being used. If the engine is in a lighter load scenario, you don't necessarily HAVE to keep a 14.7 mixture. You can dip into the 15s, 16s, and sometimes 17s in order to build efficiency. If you're under a higher load, you usually start climbing to the low 13, high 12 mixture in order to keep the motor running at those lower RPMs.

Now you also have to introduce the speed of the motor. Let's say you're churning 2200 RPMs at something like 70-80 kPa, or with deeper gears it would be 2800 RPMs at something like 40-50 kPa. Sure the higher RPM would be demanding less fuel, but certainly more injection events.

Like I said, it really depends on the tune that the OEM used at the time, and a lot of other variables that are vehicle specific. I don't think there's really a definite answer here.

I won't argue that; but putting all theory aside, I made my original comments based on practical experience.

I went from 4.10 to 4.56 with the same tires (32), and my fuel economy increased.

I put 35's on and my mileage went down.

I went to 4.88's with the same 35's and my economy increased again.


Jes, before he stopped driving his rig on the pavement, would get 19-20 on the highway with 5.13's and 35s. I get 17 mpg highway in big bird with 5.13's and 37s.

I could sit here and list practical examples where this has proven true over and over again, but at the end of the day it comes down to take my word for it or don't.

 

[87manche]

cause torque converter lockup

you can talk all day about where the 4.0 is most efficient, but if you ignore that the trans stays locked up nearly all the time with deep gears you're missing a huge part of the efficiency equation.

 

[MoparManiac]

I won't argue that; but putting all theory aside, I made my original comments based on practical experience.

I went from 4.10 to 4.56 with the same tires (32), and my fuel economy increased.

I put 35's on and my mileage went down.

I went to 4.88's with the same 35's and my economy increased again.


Jes, before he stopped driving his rig on the pavement, would get 19-20 on the highway with 5.13's and 35s. I get 17 mpg highway in big bird with 5.13's and 37s.

I could sit here and list practical examples where this has proven true over and over again, but at the end of the day it comes down to take my word for it or don't.

There are too many variables when you factor in other people and their rigs.

Same weight? Same driving style? Same location (mountains, hills, flatlands)?

And for the record, I had 4.88s and 35s and wouldn't have considered any less gearing

 

[XJEEPER]

I won't argue that; but putting all theory aside, I made my original comments based on practical experience.

I went from 4.10 to 4.56 with the same tires (32), and my fuel economy increased.

I put 35's on and my mileage went down.

I went to 4.88's with the same 35's and my economy increased again.


Jes, before he stopped driving his rig on the pavement, would get 19-20 on the highway with 5.13's and 35s. I get 17 mpg highway in big bird with 5.13's and 37s.

I could sit here and list practical examples where this has proven true over and over again, but at the end of the day it comes down to take my word for it or don't.

17-20 mpg is honorable, especially with all of the added weight, wind and rolling resistance created by lift, large tires and body armor.

I got better mileage with 4:56's and 32's than I did with 4:10's and 32's in my old rig (89) and I now average 17mpg on the highway with 4:88's and 285's (33) in a 2000 XJ with 187,000 miles 4.0/AW4.



If I were in your shoes, I'd go with 4:56's.

 

[briboki]

I had 235/75's and 4.10s and I loved it.

I now have 31's with the 4.10's and I wish I had 4.56's.

Gas mileage with 235/75's and 31's with the 4.10's was exactly the same for me.

I live at 5,000 ft and I do a lot of mountain driving.

 

[sidewaysstarion]

I won't argue that; but putting all theory aside, I made my original comments based on practical experience.

I went from 4.10 to 4.56 with the same tires (32), and my fuel economy increased.

I put 35's on and my mileage went down.

I went to 4.88's with the same 35's and my economy increased again.


Jes, before he stopped driving his rig on the pavement, would get 19-20 on the highway with 5.13's and 35s. I get 17 mpg highway in big bird with 5.13's and 37s.

I could sit here and list practical examples where this has proven true over and over again, but at the end of the day it comes down to take my word for it or don't.

The BS flag, I'm raising it :bs:

 

[techno1154]

I am yet to see someone add to the equation tire type and weight. What tires gave the best and worst fuel mileage? How does regular street/highway cruising tires with those aggressive offroad tires? I have seen tires of the same size advertised at up to 20lbs difference. Let's hear from some of you who have this experience.

One thing I do agree on though,...the OP at the end of it all have to make his own call as to the terrain on which he drives, the tire size and load in his XJ so as to select the most appropriate gear ratio.

 

[chris420]

Don't get technical with it. 4.10 is great for 31's if not overkill. Look at this way you pay a lot for new gears and labor and even though you say you will never go bigger than 31,s some day you will. There will be a day you shoot a large buck and you won't drop it then it will run into some tough terrain and you will need to drive the jeep in. I say get the 4.56 gears and while they are in there you might as well through in a detroit true trac front and Grizzley locker rear cromo shafts front and rear. Do it right the first time and you will be thankful.

 

[chris420]

I am 4.10,s on 33's MTR drive through the Nevada Sierras and Rubicon all the time Jeep spools up fine. I would like to have lower gears in the transfer case for the trail but hwy is fine just drop the overdrive.

 

[chris420]

I guess I am contradicting at times so I will be more clear. I did 4.10 gears knowingI would be putting a ford 8.8 in down the road. Everything works fine I drop down into third gear at times in the mountains but freeway speed is perfect. 4.56 gears would have been okay with 33 inch tires however I would like to have for 4.88 gears and a lower transfer case. Over gearing is okay it's easy to change tires to compensate.

 

[87manche]

something else to consider.

16" wheels and metric tires. You can get a 32 that's roughly 10" wide and split the difference with 4.56's.
they're likely to be cheaper anyhow. Identical ATM's were $30 more a tire for a 31x10.5 vs a 245/75.

 

[XJEEPER]

I guess I am contradicting at times so I will be more clear. I did 4.10 gears knowingI would be putting a ford 8.8 in down the road. Everything works fine I drop down into third gear at times in the mountains but freeway speed is perfect. 4.56 gears would have been okay with 33 inch tires however I would like to have for 4.88 gears and a lower transfer case. Over gearing is okay it's easy to change tires to compensate.

Odd, my experience is the complete opposite x 10+.

And an "easy" tire size swap to compensate for the wrong gearing selection costs what?

hasta

 

[LYKOS]

I'm really glad I found this thread.

I'm finally sinking the money into my daily driven 01 for gears, tires and new lift.

It's a camping/expo style rig.

So check my logic here.

4.56 gears with 32" tires.

My logic is with an old engine and heavy rig I'll do better with slightly lower gears. The 32's split the difference on rotating mass between the 31 and 33" tires.

That sound reasonable?

 

[Root Moose]

t's a camping/expo style rig.

So check my logic here.

4.56 gears with 32" tires.

My logic is with an old engine and heavy rig I'll do better with slightly lower gears. The 32's split the difference on rotating mass between the 31 and 33" tires.

That sound reasonable?

I'm running 4.56 and metric 32s (265/75-16), 4200 lb rig (empty, half tank of gas), ~4.5" of lift. We just returned from a ~4000 mile trip.

~70 mi/h is ~2600 RPM. It's fine, works decent enough for towing as well. I wouldn't want any lower gearing (i.e. 4.88). 4.10s would probably be fine as well but I'm glad for that extra bit of gear when fully loaded and towing a heavy camper (~8500+ lbs GCVW).

 

[LYKOS]

My experience owning big rigs is that the less throttle you use the better the fuel mileage. Heavier rigs like deeper gears, lighter rigs higher gears.

So when you add big tires, steel bumpers, roof racks etc you're engine works harder to keep all that in motion. So, especially with a tired engine, you have to throw out the charts that don't take any of that into account and go a gear deeper. Kinda like when choosing a camshaft fire a v8. You find what's perfect and go a size smaller.

Or am I just smoking bad rock?

 

[PumpinIron]

Glad I found this thread. I too am in the exact same dilemma as the OP. I have 31x10.50x15 tires and I am in the process of deciding what gears I want. I am debating between 4.10 and 4.56. In all honestly 80% of the driving I do is around town, stop-and-go. However, occasionally we take long highway trips to the beach, mountains, out of state, etc. That being said, I don't want to be at 3k RPMs on the highway where the motor is loud and obnoxious. I also want to get as best MPG as I can on the highway too so that's another consideration.

It seems like 4.10 and 4.56 is a split decision with most people.

 

[Root Moose]

31s... 4.10s. I wouldn't gear any lower for "normal" usage.