4.88 or 5.13 gears on 37 inch tires?

ERAUGrad04

New member
did you see a huge change in MPGs? for better or for worse?

I recently went from 4.10s to 5.13s at ORE. I would say I gained just a hair of fuel economy with the new 5.13s, however, at the end of the day, it's a Jeep. :)

I have been routinely seeing 15mpg-ish with the new 5.13s and 37" Trail Grapplers.
 

NV375

Caught the Bug
did you see a huge change in MPGs? for better or for worse?

I am only about 400 miles in since the regear so I don't know yet. I will be going 37s for my next tires. Going to work with the 4.10s I was in 3rd gear most of the way. Now I should be able to use 4th and 5th more.
 

dwmgcs

New member
I recently went from 4.10s to 5.13s at ORE. I would say I gained just a hair of fuel economy with the new 5.13s, however, at the end of the day, it's a Jeep. :)

I have been routinely seeing 15mpg-ish with the new 5.13s and 37" Trail Grapplers.


i went from about 12 mpg to 14 mpg, not that it matters really, mine is not a daily driver and like you said, it's a Jeep.
 

ERAUGrad04

New member
i went from about 12 mpg to 14 mpg, not that it matters really, mine is not a daily driver and like you said, it's a Jeep.

Very cool! Even though it's a Jeep, I sure would take the 2mog increase! That leaves more money in your pocket for more Jeep mods! :) :)
 

MR.Ty

Token East Coast Guy
I am only about 400 miles in since the regear so I don't know yet. I will be going 37s for my next tires. Going to work with the 4.10s I was in 3rd gear most of the way. Now I should be able to use 4th and 5th more.

Gotcha. :thumb: Like many on this thread, I'm on the same fence. Of course, now that I've changed my plan for my money, regearing is a LONG LONG ways out lol.
 

dwmgcs

New member
Very cool! Even though it's a Jeep, I sure would take the 2mog increase! That leaves more money in your pocket for more Jeep mods! :) :)

Well I think thats what this jeep thing is all about, how to find more money for mod's, lol

By the way ERAUGrad04 , looking forward to meeting you at the browns camp run, love your jeep, coming along nicely
 

ERAUGrad04

New member
Well I think thats what this jeep thing is all about, how to find more money for mod's, lol

By the way ERAUGrad04 , looking forward to meeting you at the browns camp run, love your jeep, coming along nicely

Thanks! Looking forward to meeting everyone!

We are really looking forward to that run. Looks like a great part of the country to do some wheeling. :)
 

NV375

Caught the Bug
Gotcha. :thumb: Like many on this thread, I'm on the same fence. Of course, now that I've changed my plan for my money, regearing is a LONG LONG ways out lol.

I was trying to hold out and not regear the stock axles I ended up only being able to get the front PR44 and not a rear PR 60. I also went to a 3" Enforcer lift and King 2. 5s and a bumper and winch at the same time as the gears. Any change in mileage may not be noticeable.
 

Slappy32

New member
The guys at Northridge 4x4 recommended 4.88 for my 37's when they put together my PR44 and PR60. Being a daily driver,for the first few years, I'll enjoy better gas mileage. When my JK becomes our third vehicle, I'll switch to 5.13.
 

jeffj

Caught the Bug
The guys at Northridge 4x4 recommended 4.88 for my 37's when they put together my PR44 and PR60. Being a daily driver,for the first few years, I'll enjoy better gas mileage. When my JK becomes our third vehicle, I'll switch to 5.13.

4:88 will do you a nice job with 37's.
 

mudmobeeler

Caught the Bug
The guys at Northridge 4x4 recommended 4.88 for my 37's when they put together my PR44 and PR60. Being a daily driver,for the first few years, I'll enjoy better gas mileage. When my JK becomes our third vehicle, I'll switch to 5.13.

That much better of fuel mileage to compensate for the price of a gear swap at a later date?
 

USMCvet

Banned
On a JKUR with an auto and 37's I went with 5:13's. The deal is though, I haven't finished the axle install yet. Hopefully I'll finish tomorrow or Wednesday and then align it then break in the gear sets. From the research I've done this is the combination that is going to work for me - good off road capability, good power, and descent drivability.
 

Slappy32

New member
That much better of fuel mileage to compensate for the price of a gear swap at a later date?

Honestly, I took his word for it. I asked for 5.13 and he said that 4.88 was better for the highway because of the rpms and it wanting to shift down at highway cruising speed. Knowing what I know now, I probably would have stuck to my guns. It's not a huge deal for me right now anyway.
 

jivesis

New member
I'ved looked at the ratio thread and it has the 3.6 auto with 37s and 5:13 doing nearly 3000 rpms at 60.. Seems really high to me? Shouldn't it be low 2000s?

For a dd wouldn't it be over reving?
 

ERAUGrad04

New member
I'ved looked at the ratio thread and it has the 3.6 auto with 37s and 5:13 doing nearly 3000 rpms at 60.. Seems really high to me? Shouldn't it be low 2000s?

For a dd wouldn't it be over reving?

Yeah, that's not right. I'm turning 2800-2850 at 70mph. Jeep is a 14 JKUR Auto with 5.13s and 37" Nitto Trail Grapplers.

Absolutely a perfect combo if you ask me! :thumbup:
 

Sithwindu

Member
My next big purchase is to regear, I'm in a 3.6 sport, I'll be running my 35's till they completely worn, and once down I'll go to 37's (and yes I will be purchasing a pr44 to replace the Dana 30 but prob won't be for a while, maybe mid next year) . would 4.88 be fine for a mainly daily driver on 37's that off roads occasionally (maybe 4-5 times a year)?

Or should I do 5.13's and not look back
 

dwmgcs

New member
My next big purchase is to regear, I'm in a 3.6 sport, I'll be running my 35's till they completely worn, and once down I'll go to 37's (and yes I will be purchasing a pr44 to replace the Dana 30 but prob won't be for a while, maybe mid next year) . would 4.88 be fine for a mainly daily driver on 37's that off roads occasionally (maybe 4-5 times a year)?

Or should I do 5.13's and not look back

If your running an auto trans I would go with 5.13's, with a manual you can get away with 4.88's, the difference has more to do with lack of engine braking with an auto so the the lower gears help a lot, particularly when doing a steep down hill.
 

JKAnimal

New member
I'ved looked at the ratio thread and it has the 3.6 auto with 37s and 5:13 doing nearly 3000 rpms at 60.. Seems really high to me? Shouldn't it be low 2000s?

For a dd wouldn't it be over reving?

That's incorrect. Here's the official chart and it is gauged at 70mph. For 37s and 5.13 you'll be running 2600 rpm for a manual and 2708 rpm for an auto with the 3.6L.

It's accurate because that's where my RPMs are running in my 2012 manual. You'll also have more power pulling a trailer. Green is acceptable, blue is performance and yellow is minimum.

gallery_2_46_253610.jpg
 

ERAUGrad04

New member
The charts are great to give you an idea of RPM, however, they don't tell the entire story. I belive Eddie mentions it in the regearing thread, but a Jeep with 32s and a Jeep with 37s turning the same RPM's, are not created equal. For me, going to 37s, 4.88s would have been the same RPM as stock tires and 4.10s. Sounds like 4.88s would be the obvious choice, right? Not quite.

One thing these charts don't take into consideration is increased rolling resistance and mass of the 37" tire. A 37" Nitto mounted to a Slab is easily 50lbs heavier per assembly than a factory wheel/tire. Additionally, they have a considerably larger footprint causing an increase in rolling resistance/friction. These reasons are why 5.13s are such a great combo with 37s assuming you have the D44 front axle.
 

JKAnimal

New member
The charts are great to give you an idea of RPM, however, they don't tell the entire story. I belive Eddie mentions it in the regearing thread, but a Jeep with 32s and a Jeep with 37s turning the same RPM's, are not created equal. For me, going to 37s, 4.88s would have been the same RPM as stock tires and 4.10s. Sounds like 4.88s would be the obvious choice, right? Not quite.

One thing these charts don't take into consideration is increased rolling resistance and mass of the 37" tire. A 37" Nitto mounted to a Slab is easily 50lbs heavier per assembly than a factory wheel/tire. Additionally, they have a considerably larger footprint causing an increase in rolling resistance/friction. These reasons are why 5.13s are such a great combo with 37s assuming you have the D44 front axle.

That's definitely true. It's not the whole picture, but the chart is a great place to start and does get very close. The chart doesn't reference tire pressures either, which will also change your rolling resistance. That being said, if your running 3000 rpm at 60 mph with 37s and 5.13 gears in a 3.6L, something is seriously wrong.

Is there really enough difference in mass between the different selection of 37" tires and different wheel combos to change the rolling RPM at 70mph by some huge margin? I would think it would only change within some small percentage. I'm not a tire and wheel mass expert but I did stay at a Holiday Inn Express on more than one occasion. ;)
 
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