5.13

have you used a procal or something to adjust the speedo (tire size)? I did it after installing 35s and it helped the gear search

 

Yeah, did Pro Cal speedo and tire size so I figured it's down to re-gearing.
I'm with ya... 5.13's. Do them once and forget it.
Thanks

 

Let me be the contrarian here, I had to make the same decision. Being of the opinion I'd never go beyond 35s on a JK with stock axles, I opted for 4.88s. The reason being that at cruising speed the 4.88s will have the RPMs at just over 2k, just about perfect. Using the AEV module to recal for 35" KM2s I've had no issues whatsoever with OD hunting, etc., and in low range it crawls great. JMHO, of course.

 

things to consider:

Rubi? you have 4.10 and going to 4.88 would be worthless and a waste of money

Daily driver? trail rig? daily driver/andtrail rig?

auto? stick?

35s now but ever going bigger?

no matter what you answer I would go with at least 5.13

 

I just did 5.13's w/37's. 6-sp. 1st gear is actually useful now. 6th gear at 60 mph (I did use the procal to adjust the speedo) is about 2400 rpm's, seems a bit high to me. I wonder what 5.13's and 35's would be?? Fuel economy has gotta suck... but since I don't keep track of mine and really don't care anyway, I don't really know.

 

2400 is fine..... these litle hamster wheels like high rpms

 

It's a Rubicon Auto 4.10's pulled behind an RV used mostly for trail riding.

A friend has the same setup with 4.88's and has been somewhat happy but says he'd like to go to 5.13's. But he's also considering 37's which I"m not.

Coin flip...

 

It's a Rubicon Auto 4.10's pulled behind an RV used mostly for trail riding.

auto w/35s = 5.13 NO DOUBT

 

There is a TON of info on here regarding this very issue. It took me a few minutes but I dug up a good post.

Although most of this info pertains to the manual, this is a good read as it gives you some perspective on the JK auto tranny numbers after a regear.
http://www.jkowners.com/forum/showthread.php?t=8270&highlight=stock+gears+rubi+highway

Xtremjeepn made an excellent point in that thread that you should consider:
The Auto has an INSANELY deep overdrive compared to the stick. Run this number. A Rubi, 4:10 6 speed with 35s rolling down the highway is 40 rpm(yes, 40) less than an Auto with 5:13s and 35s.

So, you'd need to go to at least 5:13's to bring it back to stock. Many have even gone to 5:38's. Once you get too deep you need to consider pinion size and contact patch. I don't know the reliability of the 5:38's on the stock d44's but from what I've read on here people are having good luck so far. If you're mostly trail riding the deeper gears are obviously a better choice for you. Furthermore, since you'll add the heavier tires/wheels you're now making that engine work even harder. This doesn't even factor in the armor and other stuff you pack in the JK when heading down the trail. If you weigh your JK once it's loaded down, you'll find that it's around 5.5K to 6K lbs.

Make sure you read this thread too. It's got some good numbers on it. http://www.jkowners.com/forum/showthread.php?t=12246&highlight=5:38's

GOOD LUCK and I hope this helps.


Tim

 

Very Helpful

Thanks for the links... great food for thought.

 

5.13's

I'm on my 4th or 5th JK in the shop and any combination of tranny and tires that were 35+ I always wished I would've gone lower than that 4.88's in the ones I regeared to 4.88

 

Thats funny I was just thinking the same thing I am getting 35s and will be regearing in feb or march but didnt know what I wanted to go to. So I am going to watch the thread

 

If you have the Dana 30 in the front I would stay with 4.88. If you play hard you will chew up the 5.13 ring gear. I went through a few.I was fine just playing on the trail rides but when I started to run it in the comps. You play a little harder and then you get that oh so familiar sound of teeth stripping.

 

I have never seen a post about properly installed gears on a JK failing with 37" or smaller tires unless it was part of a catastrophic failure that would have damaged any size gears.

So, the evidence would suggest that the gearset is not the weak link in JK axles and you shouldn't worry about putting 5.13s in a JK Dana 30, or 5.38s in a JK Dana 44. If you have seen a compelling number of JK gearset failures due to small gear teeth, please point them at least one out to me on any forum.

As a result, with an automatic, I'd go absolutely as low as you can go. For a Rubi, that is 5.38s, for a non-Rubi, that is 5.13s.

The JK engines require higher rpm levels than the old 4.0L TJ engines. They really need to be run over 2500 rpm at highway speeds to produce enough rear wheel horsepower to drive in windy situations, towing, up grades, or at higher elevations to avoid flashing the converter (downshifting with tranny slip that revs the rpm levels higher than they would otherwise be in just 3rd gear with the overdrive off). I am not an engineer or a rocket scientist, but I can tell you that 64 rear wheel horsepower at 2k rpm is not adequate to roll 35" tires on a non-aerodynamic brick of a lifted JK in windy, towing, graded/hilly, or higher elevation (i.e. Rocky Mountain West) situation. Maybe on low elevation, flat highways, on 2 doors, with little or no lift 64 rear wheel horspower at 2k rpm is sufficient, but not for the rest of us.

Gas mileage will improve for automatics that run at 2500 rpm at highway speeds due to the reduced flashing of the converter (downshifting, etc.).

This is not opinion or casual observation. Clearly, the automatic JKs are undergeared stock and the Rubi's should have come with 4.56s or 4.88s stock.

Here is the evidence of the JK rear wheel horspower at different rpm levels:

Here are the rpm levels by tranny type, gear, and tire size (notice that the rpm levels of 5.38s are barely more than 5.13s, making 5.38s preferable with an automatic Rubi with 35" or taller tires):

 

Would GR apply to me?



I have a 6spd 06 Rubi with 4.0. I use the thing a lot on highway @ 70-75 mph. I hate seeing the engine rev so high. In 6th I tach 2700 @ 70mph. Can I use this chart to select a larger tire to stay in the green range yet give the engine a break? My 4.0 91 Wrangler (5spd) was in the 2200 range at these speeds if I remember correctly and that engine was running like a top when I sold the Jeep @ 197,000 miles. Great post by the way.

Bob D

 

Good post.

 

Ok so which brand would be the best to go with? Alloy usa , motive gear or the g2?

 

Anyone got a good choice or best brand of gears to go with?

 

I would just call one of the supporting vendors here and ask their opinion--probably Phil (owns Trail Duty).

 

I went with the Yukon gears, Im sure others are ok as well. most are made by the same manufacter and relabled before sale. but to be safe. Go with Yukon.

 

So alot of people say since this is my daily driver 4.88s would be the way to go but then othrs say all the weight you add you should do 5.13s damn such a hard choice

 

I am trying to make the same choice and honestly after talking with some people and riding in a guys with the 5.13 gears I am now set at 5.13's and actually if I had the front dana 44 I would be doing 5.38's

My Jeep is a daily driver but I think that the 4.88's will fall short of some of my expectations and the difference between the 4.10's and the 4.88's does not really backup the price as the 5.13's do.

 

they should put 4.88s in stock. go with the 5.13s.

i have 5.38s in and love them.

 

i have the been wondering about the gear manufacturers. i hear about noisy gears with some brands. i understand yukon is made in china. is there a quality American made set of gears available? i would like to run a 4.56 with my 6 speed as i don't think i will go over a 35 inch tire, let alone allot of advertised 35 inch tires are more like 34"

 

"is there a quality American made set of gears available?"

X2

 

I got 5.13 installed, running an auto. I was turning about 3100 at 80, and turning about 2800 at 70, with 33' Kumho Road Venture MTs that are rated from the maufacturer actually closer to a 32". The around town was perfect, but the highway was maybe a tad too much rpm. And I mean just a tad. I just put on a set of Goodyear Wrangler MTRs today that are a 35x12.5x15. I havent had a chance to properly evaluate the highway manners, but so far in the city I wish I had gone to a 5.23 with the 35s. I think that would have made it a better overall arrangement then 33s and the 5.13s. However keep in mind my 33s were a bit on the short side compared to other brands. I am also running the Superchips Flashpaq on teh 87 octane performance tune.

 

I have 3.73 auto unlimited. I towed a 6x12 trailer up and down some hilly highway and I agree with the mid-range RPMs. I had overdrive off with 35" toyo's going avg of 70 mph. My RPMs were around 27K sometimes 31K. It ran like a champ. At first I was thinking "too high, too high" heck no. If it had to down shift it would go to about 41K but at 27-32 it was a champ. easy to maintain speed and heck, there were times I was passing cars on both freeway hills and highway slopes. If I remember the trailer was around 3400 to 3700lbs