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Discussion Starter · #1 ·
Hey guys,

2014 JK running 35x12.5x15 mtrs with kevlar.

I am regearing, adding lockers and gusseting/trussing both my dana 30 & 44.

I am stuck on my gear ratio right now... I do a lot of crawling and wanted the lower gearing but I am concerned about stuffing 4.88 into the dana 30?

Would I be safer with the 4.56? I have a 6 speed and am mostly just concerned with being able to crawl over stuff without much gas.

Thanks
 

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Others will have more knowledge but personally, when I get the money to go 35's I'm going with 4.88's. I have an auto and have yet to go off-road, but I want the higher RPM's.

So, my opinion would be 4.88, especially since you said you dont want to use the gas much off-road.
 

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There is also the option of cryo-treating the gears to make them stronger. Look to see if you can find someone local that does this - or a shop familiar with it. Fairly cheap.

I think 4.88 should be ok. Being able to crawl over stuff in idle slow motion is totally awesome. A world of difference. You wont be able to crawl as low as a Rubicon with the 4:1 transfercase (I think other models are 2.72 or 2.73), but should be dramatically better than what you have at stock gearing. Good luck with your build!
 

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4.88 is what I think they recommend with 35's and manual trans in the 3.6 for optimum split on and off road performance. I have 4.56 in an auto and 35's. Its my daily driver and I drive about 20K miles a year in it so I wanted a little lower RPM on the highway. The installer did try to talk me into 4.88's, but coming from 3.21's, the gears I got feel like night and day. I'm happy with it.
 

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Hey guys,

2014 JK running 35x12.5x15 mtrs with kevlar.

I am regearing, adding lockers and gusseting/trussing both my dana 30 & 44.

I am stuck on my gear ratio right now... I do a lot of crawling and wanted the lower gearing but I am concerned about stuffing 4.88 into the dana 30?

Would I be safer with the 4.56? I have a 6 speed and am mostly just concerned with being able to crawl over stuff without much gas.

Thanks
if your only concern is crawl then 4.88 will get you a lower crawl but will sky rocket your cruizing rpms

HONESTLY the best way to do that if your staying with 35s is to swap your tcase for a rubi case. Im running 4.56 gears on 37s manual trans and 3.6 runs out perfect but i have a rubicon so my crawl ratio is stupid low already. I wouldnt regear on 35s unless you are on 3.21. if you are running 3.21 id go with a 4.56 just in case you ever want bigger. if on 3.73 id leave em and swap to a rubi case for about the same money as a regear if not cheaper.

with 4.88 you will be turning 2600rpms to do 70mph
with 4.56 you will be turning 2400rpms to do 70mph
with 3.73 you will be turning 2000rpms to do 70mph


conversely you care about your crawl ratio so ill put that on here too

with 3.73 and a sport case you will have 45-1 crawl ratio and 1st gear 750rpms will take you 152 fpm

with 3.73 and a rubi case you will have a 66-1 crawl ratio and 1st gear 750rpms will take you 103 fpm

with 4.56 and a sport case you will have a 55-1 crawl ratio and 1st gear 750rpms will take you 125 fpm

with 4.88 and a sport case you will have a 59-1 crawl ratio and 1st gear 750rpms will take you 117 rpm


and for reference
my jeep on 37s with a rubi case and 4.56 gears has a crawl ratio of 81-1 and does 89 FPM
I use 1st for low speed crawling where I hardly ever use the gas. plenty of torque available. My second gear will do 153 fpm and I use it more for easy cruising over rough terrain.

So if crawl is your concern then swap the case. if you dont like the day to day drive and want a little more launch of the line. Id go 4.56 the extra little bit of slower crawl out of 4.88 would not be enough for me to justify turning 2600rpms on the highway
 

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I had 4:88's installed last month They are great. I finally get to use my 6th gear now which I really never got to use with 3:73 and 32" tires.
 

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Discussion Starter · #7 ·
if your only concern is crawl then 4.88 will get you a lower crawl but will sky rocket your cruizing rpms

HONESTLY the best way to do that if your staying with 35s is to swap your tcase for a rubi case. Im running 4.56 gears on 37s manual trans and 3.6 runs out perfect but i have a rubicon so my crawl ratio is stupid low already. I wouldnt regear on 35s unless you are on 3.21. if you are running 3.21 id go with a 4.56 just in case you ever want bigger. if on 3.73 id leave em and swap to a rubi case for about the same money as a regear if not cheaper.

with 4.88 you will be turning 2600rpms to do 70mph
with 4.56 you will be turning 2400rpms to do 70mph
with 3.73 you will be turning 2000rpms to do 70mph


conversely you care about your crawl ratio so ill put that on here too

with 3.73 and a sport case you will have 45-1 crawl ratio and 1st gear 750rpms will take you 152 fpm

with 3.73 and a rubi case you will have a 66-1 crawl ratio and 1st gear 750rpms will take you 103 fpm

with 4.56 and a sport case you will have a 55-1 crawl ratio and 1st gear 750rpms will take you 125 fpm

with 4.88 and a sport case you will have a 59-1 crawl ratio and 1st gear 750rpms will take you 117 rpm


and for reference
my jeep on 37s with a rubi case and 4.56 gears has a crawl ratio of 81-1 and does 89 FPM
I use 1st for low speed crawling where I hardly ever use the gas. plenty of torque available. My second gear will do 153 fpm and I use it more for easy cruising over rough terrain.

So if crawl is your concern then swap the case. if you dont like the day to day drive and want a little more launch of the line. Id go 4.56 the extra little bit of slower crawl out of 4.88 would not be enough for me to justify turning 2600rpms on the highway

I have 3.21's so I'm definitely regearing... problem is I live in Canada with a small population so the chances of finding a used rubicon Tcase is literally impossible...

Where are you getting your data from? 4.88s at 70mph is that RPM in 6th gear?
 

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Where are you getting your data from? 4.88s at 70mph is that RPM in 6th gear?
Must be with the manual in 6th. With the 5 speed auto at 70 MPH in 5th gear and 4.56 I turn about 2650 RPM's.
 

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I have 4.56 gears with 35's and a 6 speed manual and Pentastar. It's great for driving around and for moderate trail riding. But since my Jeep is a Sport it has the 2.72 low range Tcase. I can't crawl very well because I don't have a low enough low range. When I'm on a ledge I either stall or give it too much gas and lose traction. A Rubicon case would make a huge difference. But even around here they're hard to find. I may end up going with an Atlas instead.
 

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yeah. and the calculator says you would be turning 2722. but you probably arent actually running a true 70.

my speedo was off bad from the factory (like 5mph at 70 stock) when i calibrated it i cal'd it at 70 and ended up punching in a 35.5in tire into the flash cal when im on 37s to get it to read dead on at 70
 

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yeah. and the calculator says you would be turning 2722. but you probably arent actually running a true 70.

my speedo was off bad from the factory (like 5mph at 70 stock) when i calibrated it i cal'd it at 70 and ended up punching in a 35.5in tire into the flash cal when im on 37s to get it to read dead on at 70
That's because almost no tire in existence measures as big as the advertised size. It's the difference between what the specs are on paper and the way things actually work in the real world.

If you put in the actual real world rolling diameter of your tire the calculator is spot on. If you insist on using published specs instead, you'll be off. Garbage in, garbage out.
 

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That's because almost no tire in existence measures as big as the advertised size. It's the difference between what the specs are on paper and the way things actually work in the real world.

If you put in the actual real world rolling diameter of your tire the calculator is spot on. If you insist on using published specs instead, you'll be off. Garbage in, garbage out.
Yep. there is that too. my MTRs were like a 34.5 mounted but they looked huge next to the same size km2. witch was closer to a true 34. my 37s look big but they are probably a 36.25 in reality. the 13.5 width makes them look monstrous
 

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Neat. never had a need for that so I never noticed it. :beerdrinking:
It's easy to overlook. I may do something to make it stick out more next time I update it. But with spring teasing us I'm probably going to be up in the mountain trails for the next few weekends.
 

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Yep. there is that too. my MTRs were like a 34.5 mounted but they looked huge next to the same size km2. witch was closer to a true 34. my 37s look big but they are probably a 36.25 in reality. the 13.5 width makes them look monstrous
My Duratracs say they're a 35 but I had to tell my computer 33.48" to get the speedo to match the GPS. With that same size in the calculator it came out almost exactly right. My factory 255/75R15s were advertised at 32.1 but the computer was programmed at 31.01 to get the speedo accurate.
 

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yeah same here. i love the calculator it gives much better info than those stupid charts everyone has.
 

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With 5.13 and 37s, I can truly crawl the 4:1 transfercase. I built my rig to crawl - street performance was only secondary. 5.38 would have been amazing offroad but just too low on street IMHO. It is all about balance. I am an automatic.

2700+rpm is not a bad thing in the 3.6 like it may have been in older engines. I am not sure how true it is but read somewhere Pentastar 3.6 hits its optimum power band somewhere around 2800-3000rpm.
 
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