Gears for 37" tires

[TennesseePA]

In the end we are all free to do what we think is best. I personally believe that my JT on 37s and stock gears is a great combination. My truck is not a garage princess I use it every day and since I took delivery on June 25 I have already put 12,700 miles on it. I have towed my enclosed trailer from Nashville to Destin twice and to Gatlinburg, TN twice. Every trip was an empty to the destination and loaded with antique oak furniture on the way home. I tow my 6x10 utility trailer at least three days a week and it performs amazingly. TN is not a flat place, we have some very good hills around here with some very long climbs, BUT, I will concede that there is a big difference between the 600 ft elevation of Nashville and the western states.

My wife has a Nissan Quest with the CVT and it is the perfect example of how a transmission should work. The computer calculates the load and the work that needs to be done and adjusts the transmission to put the engine at its most efficient RPM. If you have never driven a CVT when you floor it the engine RPMs climb to a certain level and then remain there as you continue to accelerate. Like I said earlier it puts the engine in the best spot and adjusts the gear ratios to produce acceleration. The JT 8 speed does the exact same thing just with fixed ratios, and it does it very well.

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[JCJL]

You're the first to complain about that video but I guess that's the beauty of opinion.

That chart is BS tho all the numbers are completely wrong.

4.88 and 70mph on 37s will turn 2078 rpms
Same setup in 5.13 gears will turn 2185 at 70mph that chart is off by a LOT.

Try this instead.
http://www.grimmjeeper.com/gears.html
Your chart might be for a JK but it's clearly not for. JT or JL

That's spot on with mine.

 

[Ericshere03]

These threads never seem to provide a satisfactory answer for everyone. But I wanted to share one datapoint. There is a vehicle out there that is a similar engine displacement, also it requires some RPMs for power (as apposed to the tractorlike TJ 4.0), it also has a similar 6 speed manual transmission, similar weight and size...

Anyone want to take a guess? ... well its the Tacoma, and they feel it right to pair their platform with 4.30 gears and 32" tires. Extrapolate that information and the 4.88 seems to be the answer based on Toyota engineering (i know its more complicated then that).

I have NO IDEA why they gear these dang gutless motors so low, like an old chevy V8.

My Jeep TJ was built stock with a .84 OD and 4.10 gears on 31" tires... Thats a ton of RPM for a motor that done with life at 4000RPM. But in the end it worked and never had complaints on the power (once you accept that the jeep ISNT a V8).

I Just picked up my gladiator 6 speed (also owned 2 LJ's, 2 TJ's and 2 JK's [3.6], all manual transmissions). I KNOW 35's will be in its near future, and I dont want to spoil the jeep with it being geared too low (one JK came stock with 3.21 and 32" tires [Winter Edition] HORRIBLE). I expect I will be on the 4.88 bandwagon since I'd like to tow a small travel trailer.

Again, all the above are my opinions and experiences. The Gladiator is really a great vehicle, further from a true jeep but a better all around vehicle.

 

[NFRs2000NYC]

Another key issue I don't think I saw mentioned is pinion size. Not sure if anyone has a photo of the pinion size of a 4.10 pinion vs a 4.88 and 5.13, but from what I recall on the JK, the 5.13 pinion is considerably smaller than the 4.10 while the 4.88 is slightly smaller....and with turning larger tires, especially through mud, deep snow, and obstacles, it can be a weakpoint you didn't want. So, is it worth the little bit of extra pep? I guess depends on who you ask.

 

[ShadowsPapa]

I have NO IDEA why they gear these dang gutless motors so low, like an old chevy V8.

.

That's easy - HP through speed. In the earlier V8 engines you got HP through cubic inches and air flow. Now it's smaller cubes at higher RPM.
The dyno sheets tell a story as does history of engine development.
The redline on modern engines is way above what the blow-up point was on earlier engines. Parts smaller, lighter, spin up faster.
Even my Chevy LS needed high RPM to make power - it wasn't so great at lower RPM while my 360 would do very well at 2,000 rpm less.

 

[Ericshere03]

Another key issue I don't think I saw mentioned is pinion size. Not sure if anyone has a photo of the pinion size of a 4.10 pinion vs a 4.88 and 5.13, but from what I recall on the JK, the 5.13 pinion is considerably smaller than the 4.10 while the 4.88 is slightly smaller....and with turning larger tires, especially through mud, deep snow, and obstacles, it can be a weakpoint you didn't want. So, is it worth the little bit of extra pep? I guess depends on who you ask.

I don’t think it’s that big a deal on a D44 until you get into the 5’s ... 4.88 and even 5.13 should be plenty stout.

 

[Factoid]

There’s always the 60...

 

[NFRs2000NYC]

I don’t think it’s that big a deal on a D44 until you get into the 5’s ... 4.88 and even 5.13 should be plenty stout.

Not the point. The point is, both the 4.88 AND the 5.13 are smaller than 4.10...and that smaller is a certain amount of %.....as a result, it IS weaker. Coupled with the torque multiplication, and that % starts to matter. Does it for most? Probably not. However, IMHO, it is definitely something to consider, not just the RPM range and the extra pep....that pep isn't free. Weighing down the vehicle, larger tires, etc, can create a trail break you didn't want. For some, the extra little bit of strength from a 4.88 vs the extra little bit of pep from the 5.13s would be the option they choose.

 

[ShadowsPapa]

Shaft sizes will be the same. Tooth contact would be my only issue and I'd want to study the contact patterns of each.
The core shaft size is the smallest part of a pinion. The weakest is the tooth contact area. So if the contact area is the same, the base of the tooth still rooted similarly......
Breaking a pinion - talk to the guys that launch a 600+ hp car to do a quarter in under 7 seconds at about 180 mph about pinion strength. Anyone here put out that sort of HP or torque?
Transmission shafts, axles, driveshafts - rarely a pinion.

Just tossing out random thoughts from a random mind with random opinions.

 

[Ericshere03]

Not the point. The point is, both the 4.88 AND the 5.13 are smaller than 4.10...and that smaller is a certain amount of %.....as a result, it IS weaker. Coupled with the torque multiplication, and that % starts to matter. Does it for most? Probably not. However, IMHO, it is definitely something to consider, not just the RPM range and the extra pep....that pep isn't free. Weighing down the vehicle, larger tires, etc, can create a trail break you didn't want. For some, the extra little bit of strength from a 4.88 vs the extra little bit of pep from the 5.13s would be the option they choose.

I think we are creating an issue that doesn't exist. Dana themselves make 4.88 and 5.13 gearsets, I am sure the strength of those ratios passes their designed torque input rating without compromise. In other words, these differentials are designed to support the deeper gears that Dana themselves provide. Also, these engines arent exactly torque monsters.

But this argument was beat to death when JK's were new. and even TJ's when the rubicon came out with the ability to exceed 4.88 ratios (Aftermarket 5.13 and later 5.38). Bottom line, if you are breaking these D44 axles, even with 5.13, then your really in need of Dana 60's.

That all being said, when I install 4.56 or 4.88, I will be using Dana gears and axle kits, just for piece of mind.

 

[NFRs2000NYC]

Yes but those gearsets are meant to get the vehicle to stock parameters (nevermind the fact that dana axles are used all over the place not just JT/JL/JK) so they dont necessarily engineer them to run with a specific tire size/weight.

 

[davetha]

There’s always the 60...

or 14 bolt, or Dana 80. I like the fact the Dana 60 axles have E-Locker options which work with the factory rubicon locker switches. I have a set of 40x13.5R17 Maxxis tires on beadlocks that would sure look pretty on my gladiator, but I can't commit to it right now

Either way, if I slap on 37s on mine. I'll just jump to 5.13. The slight uptick in RPM isn't going to be noticeable. Now on my old TJ with 5.38s and running 35s for a couple of days... yeah it would get close to redline.

 

[TRAILJT]

Hello Everyone. I just dropped my Gladiator Rubi off yesterday to get re geared. I am running 37s on 17" wheels and had not been happy with the way my truck can't make up its mind on which gear it wants to be in while on the freeway. So I went with 4.88s. I should have my truck back tomorrow if everything goes well. I used yukon gears and Yukon master kits and am installing red ARB diff covers. I am excited to get some of my power back and hopefully see a tiny gain in fuel mileage. Ill keep everyone posted on how it feels after the break in period. Happy Trails!

 

[Daniel.cox8]

Did you have a tuner to set your gear ratio in the computer? What did you use

 

[TRAILJT]

Did you have a tuner to set your gear ratio in the computer? What did you use

Hello, Yes I do have a calibrator not a tuner. I can't get a tuner sent to me in California. Plus I don't want to void my warranty. I use a rough country calibrator. I calibrated for the tires. I am getting my truck back today. I will calibrate for the gears before I leave the guys place that is doing my gears.

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