Swapping up to the 4.10s

[Wheelin98TJ]

Don't care, he's making a second mistake. The first was buying a diesel.

Diesel or gas matters when it comes to axle gears.

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[Steven_B]

For reference. "37" inch Nitto Recon ATs with 4.10 gears. Been running this combo for a few years and love it. And my Jeep is about 7,000 lbs fully loaded.

 

[TheSolarWizard]

there's a lot of weird stuff going on in this thread for seemingly zero reason other than being argumentative

there are other things to be concerned with on the diesel besides mpg and rpm. namely EGTs but also boost and a couple other ancillary items. from an mpg perspective you cannot get to stock mpg obvious because of physics. BUT if you're ultimate focus is on freeway mpg, leaving the gearing alone will net the best results.
The problem is the EGTs will stay hotter for longer and the turbo will be making boost longer. These obviously go hand in hand. if you haven't fixed the other problem with the diesels beforehand, this problem is exacerbated.

here's the 'best' way to calculate for gearing/tire changes

stock tire size / stock gearing = new tire size / X gearing. solve for x.

the stock sport/overland gets better economy on the diesel. partly due to weight but MOSTLY due to RPM range given the lack of aerodynamics on the freeway and partly due to rolling resistance .

32 / 3.73 = 38 / X
3.73 x 38 =141.74 / 32 = 4.42 rounding up for tire size = 4.56

I've been in dozens and dozens of modified diesel JL/JTs and I can say for sure that the BEST gear ratio for 38s on them is 4.56 which is backed up by the simple algebra. 4.11s will still drive better than stock gearing but the EGTs will benefit more from being slightly over.

for the record, Currie, Fusion, Rockkrawler and several other well regarded shops and manufacturers readily agree with this. I can't say for sure how all of them came to that conclusion but I know for sure that Rockkrawler & currie both spent money and lots of time running multiple gear ratios and multiple tire sizes on diesels while monitoring quite a few parameters and just paying attention to drivability both on and off-road.


there's a chart for reference on this page
https://www.currie4x4.com/currie-extreme-60-jeep-gladiator-jt-axle-assemblies

 

[Ericshere03]

there's a lot of weird stuff going on in this thread for seemingly zero reason other than being argumentative

there are other things to be concerned with on the diesel besides mpg and rpm. namely EGTs but also boost and a couple other ancillary items. from an mpg perspective you cannot get to stock mpg obvious because of physics. BUT if you're ultimate focus is on freeway mpg, leaving the gearing alone will net the best results.
The problem is the EGTs will stay hotter for longer and the turbo will be making boost longer. These obviously go hand in hand. if you haven't fixed the other problem with the diesels beforehand, this problem is exacerbated.

here's the 'best' way to calculate for gearing/tire changes

stock tire size / stock gearing = new tire size / X gearing. solve for x.

the stock sport/overland gets better economy on the diesel. partly due to weight but MOSTLY due to RPM range given the lack of aerodynamics on the freeway and partly due to rolling resistance .

32 / 3.73 = 38 / X
3.73 x 38 =141.74 / 32 = 4.42 rounding up for tire size = 4.56

I've been in dozens and dozens of modified diesel JL/JTs and I can say for sure that the BEST gear ratio for 38s on them is 4.56 which is backed up by the simple algebra. 4.11s will still drive better than stock gearing but the EGTs will benefit more from being slightly over.

for the record, Currie, Fusion, Rockkrawler and several other well regarded shops and manufacturers readily agree with this. I can't say for sure how all of them came to that conclusion but I know for sure that Rockkrawler & currie both spent money and lots of time running multiple gear ratios and multiple tire sizes on diesels while monitoring quite a few parameters and just paying attention to drivability both on and off-road.


there's a chart for reference on this page
https://www.currie4x4.com/currie-extreme-60-jeep-gladiator-jt-axle-assemblies

I do not think you can make your claim without reviewing the BSFC charts for the ecodiesel … as an experiment, I ran the freeway portion of my 17mi commute in 7th gear with my 37’s (stock 3.73 gears), which is almost exactly the same final ratio as 4.56 in 8th… I cannot detect a difference in fuel mileage.

I will say that the turbo is more “alive” and able to provide instant power without spooling up, which is nice.

I’d like to see measurements, but 1600rpm at 70 might produce higher EGT than 2100 at 70 would.

I’d also state that 2100rpm is still not really pushing the ROM of this little motor. I feel my buddies 6.7l Cummins pushed more rpms than my ecodiesel… 6 speed auto vs our 8 speed double overdrive auto.

 

[Snowcavemike]

Pulled the trigger today and ordered the Spicer 4.10s from the gasser and Master Install kits.

Don't want to lose the top end highway mpgs that would come from upping to the 4.56s.

Since adding the Mopar 2" lift and going up to Nitto Ridge Grappler 38x11.50r17 last Saturday, I have felt the need to bring the power band back closer to oem spec.

The actual 37" tire on the truck dropped the ratio to 3.3 and effected what I feel is unacceptable fuel consumption at launch from stop.

I ran Nitto Trail Grappler 35x12.5x17 for the last 3 years and felt the 3.73 ( 3.55 due to 35" tire size ) was adequate since I don't tow and live in Flat Earth Florida

Tire Size Gear Calculator sez 4.22 to get back to oem spec, so it will end up being. 12 underdriven with 4.10s.

That small amount of underdrive should be acceptable at launch and give a fraction better highway mpgs.

It's recomended not to regear on the diesel. I'm running 37's in hilly California. One of the issues is heat build up. The folks who put a bigger differential cover on have better luck when they regear

 

['22JTRD]

My advice, don't do it. I have a JTR with 4:10's and 37's.

A gasser with oem 4.10s going from oem 33s up to a 37s (36ish actual measured height) would need a 4.56 Ratio to get back close to oem power band.

I understand your disappointment of the performance with 37s on the oem 4.10 with the 3.6 gas motor.

Your effective ratio with a measured 36" tire and 4.10s actually dropped to 3.76 and a new 4.47 would bring that back to spec. The 4.56 is the closest.

I have done the algebra, checked multiple online Calculators and Gear Swap Charts.

For what ratios are offered by Spicer, the 4.10 ratio is what my truck needs.

Thanks for trying to help.

 

['22JTRD]

"TheSolarWizard, post: 1520303, member: 23291"]
there's a lot of weird stuff going on in this thread for seemingly zero reason

Two things you're missing here.

One

My 38s actually measured at 37 on the ground.

Rubicon oem 285 tire is 33". I measured mine at new at 300 miles when I went to 35s

Using 37 , 33 and the Diesel 3.73 for the math , the answer is 4.10.

Two

Running oem spec rpms doesn't increase EGT.

Running a higher 4.56 gear at the same speed will raise the RPMs and EGT.

 

[CrazyCooter]

You are all wrong.....I once had a Peterbilt and I hated the 3.90's.....3.31's are the ticket!

Crazy how people keep popping in here basing stuff on a complete different scenario......I'm back to checked out of this forum because of the useless database filling info!

 

[TheSolarWizard]

as an experiment, I ran the freeway portion of my 17mi commute in 7th gear with my 37’s (stock 3.73 gears), which is almost exactly the same final ratio as 4.56 in 8th… I cannot detect a difference in fuel mileage.

I will say that the turbo is more “alive” and able to provide instant power without spooling up, which is nice.

I feel like you just made my point for me. The difference between 4.1 & 4.56 will be how often the transmission hunts for a gear on the freeway. The first 5 gears are gone so rapidly that the difference is irrelevant.

Whether you detected a difference in mpg or not depends on a myriad of factors like ground speed and wind direction.

I personally tested 3 diesel gladiators at 72 gps verified mph (where my data shows is the max speed before mpg really starts falling on this platform) on some of the flattest smoothest freeway on I-8 in Arizona because im a data dork and I hate spending money twice.
My JT at the time had 39 KM3s on stock gears
1 jeep had 4.11 gas rubicon axles on 38 ridge grapplers (virtually identical in true height)
1 jeep had 39 km3s on 4.56 gears.

106 mile loop
Best mpg was mine at 23.1 but it was in 7th whenever the wind was working against me and want 5th or 6th to execute a freeway takeover pass

worst mpg was 4.56s at 21.7 but leisurely passed in 8th and 7th was great for anything else

4.11s came in at 22.1 mpg was fine but still wanted 7th to a casual pass and 6th for passing the more correct way.

I did not have the opportunity to record temperatures with the equipment I had but the 4.56 ran the coolest oil temp and EGTs were down almost 200* at peak below the other two.

is this a perfect way to gauge this? No of course not but my decision to chose was easy after this test. If you like to run 80-85, 4.11s may be better thats hard for me to say. I drive 75 or under 90% of the time on the road.

I ended up going way more extreme with the mods and stuff so that time was more or less wasted on but im hoping someone can benefit from it. Good luck

 

[Stan H]

I feel like you just made my point for me. The difference between 4.1 & 4.56 will be how often the transmission hunts for a gear on the freeway. The first 5 gears are gone so rapidly that the difference is irrelevant.

Whether you detected a difference in mpg or not depends on a myriad of factors like ground speed and wind direction.

I personally tested 3 diesel gladiators at 72 gps verified mph (where my data shows is the max speed before mpg really starts falling on this platform) on some of the flattest smoothest freeway on I-8 in Arizona because im a data dork and I hate spending money twice.
My JT at the time had 39 KM3s on stock gears
1 jeep had 4.11 gas rubicon axles on 38 ridge grapplers (virtually identical in true height)
1 jeep had 39 km3s on 4.56 gears.

106 mile loop
Best mpg was mine at 23.1 but it was in 7th whenever the wind was working against me and want 5th or 6th to execute a freeway takeover pass

worst mpg was 4.56s at 21.7 but leisurely passed in 8th and 7th was great for anything else

4.11s came in at 22.1 mpg was fine but still wanted 7th to a casual pass and 6th for passing the more correct way.

I did not have the opportunity to record temperatures with the equipment I had but the 4.56 ran the coolest oil temp and EGTs were down almost 200* at peak below the other two.

is this a perfect way to gauge this? No of course not but my decision to chose was easy after this test. If you like to run 80-85, 4.11s may be better thats hard for me to say. I drive 75 or under 90% of the time on the road.

I ended up going way more extreme with the mods and stuff so that time was more or less wasted on but im hoping someone can benefit from it. Good luck

To me living in hill and Mountain terrain and 80% backwoods those mileage differences dont mean squat . It's the torque and power that I would be after I would have went with the lowest reduction and call it good .
Which did you take ?

 

[Vtur]

It quite simple. The higher the rpm, the less load and boost requires at given speed, equal running cooler.

Those who drives a manual can easily understand this.

 

[NCJL]

Real world.
42’s with 5.13’s. Just did a 300 mile loop thru central NM. Half highway/half Desert. Averaged 21.5 MPG. The JTRD weighs about 7K.
I was averaging 75/80 MPH on the highway portion of the trip. When I average less than 75mph I can get an extra mile or two MPG. 75MPH is about 2100RPM.
I have also driven a JTRD with 5.38’s and 42’s. Both are very similar. I prefer the 5.13’s.

When AEV was building new JTRD’s. They installed 4.56’s with 37’s. Currie recommends the same.

The Non-Rubicon’s JTD’s from the factory had 31’s with 3.73’s and a higher MPG listed on the MSRP sheet.

 

[Rusty PW]

You are all wrong.....I once had a Peterbilt and I hated the 3.90's.....3.31's are the ticket!

Crazy how people keep popping in here basing stuff on a complete different scenario......I'm back to checked out of this forum because of the useless database filling info!

I was wondering when you would pop up.

 

[CrazyCooter]

I was wondering when you would pop up.

LOL.....I've replied to probably dozens of threads in the past, but there still seems to be a need to hash this same situation out by creating yet another thread..........

"But I have a different brand of 37's and my Gladiator is a different color so I'm special case. Would 6.17's and 27's be a good combo for towing a 30K goosneck? Will I still have overheating problems climbing a 25% grade at 128°F? Will this void my 125K extended warranty? Anyone know of a good gooseneck off the shelf under $100 that fits without welding? I don't want to weld on my frame and void the warranty and potentially crack it. Will the Red Air lifts be enough for the 7500lb hitch weight? Should I truss the axles to help?" Should I keep going?

I'm going for the 50/50 snarky vs informative approach. People seem to get pretty butt hurt these days when you "Google it for them"!

 

[CrazyCooter]

Even AI recommends 5.13's, but you could get by with 4.88's!

https://www.google.com/search?q=what+gears+should+I+run+with+37s+on+a+diesel+gladiator&client=firefox-b-1-d&sca_esv=b3e0f23ec436779b&sxsrf=AHTn8zrQlSeIaN1P47vWptYsnJRe9bJUyA:1747700558179&ei=TssraLHBCu3NkPIPoKXkwQ4&ved=0ahUKEwixoMb347CNAxXtJkQIHaASOegQ4dUDCBA&oq=what+gears+should+I+run+with+37s+on+a+diesle+gladiator&gs_lp=Egxnd3Mtd2l6LXNlcnAiNndoYXQgZ2VhcnMgc2hvdWxkIEkgcnVuIHdpdGggMzdzIG9uIGEgZGllc2xlIGdsYWRpYXRvcjIEEAAYRzIEEAAYRzIEEAAYRzIEEAAYRzIEEAAYRzIEEAAYRzIEEAAYRzIEEAAYR0jgCFAAWABwAHgCkAEAmAEAoAEAqgEAuAEMyAEAmAIBoAIJmAMA4gMFEgExIECIBgGQBgiSBwExoAcAsgcAuAcA&sclient=gws-wiz-serp

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