4.88 or 5.13?

[JohnJG]

Just for the record, going to any higher numerical number is actually considered lower gears because...oh heck, I’m not going to explain it.

Yeah. I was scratching my head from some of the posts. I'm thinking "Wait. What? That's not right."

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[Irishjl]

I do not think you are stupid, I agree with everything you said. I too prefer deep gears in my vehicles. I am currently running 5.13's In a JLUR 6 speed with 35's. With two overdrive gears in Jeeps JLs they are still easy to drive on the interstate even with 5.13's. Why not consider 5.38's? cause you know your going to run 37's someday, maybe even 40's, plus gears make for a great foundation for other mods.

Does having 5.13’s and 6 speed make it a pain to drive at slower speeds? Shifting a lot. I have the same but a spot and was thinking of getting the same gears.

 

[mickey3]

Does having 5.13’s and 6 speed make it a pain to drive at slower speeds? Shifting a lot. I have the same but a spot and was thinking of getting the same gears.

I think that the JL with a six speed is better at slow speeds with 5.13's than it was stock. My wife drives this thing every day, and she continues to comment on how much she prefers the new gears. First gear is a little short, but after that everything seems as it should be. I think you will actually be shifting less, because you will have less need to down shift on hills and when you slow to make a turn at an intersection. I was slipping the clutch a lot, in and out of driveways, now the engine pulls better in those situations. Btw, this set up does not feel radical, in fact this is the way FCA should produce this Jeep. Let us know what you decide to do, as I would be interested in your opinion of the gear change.

 

[rustyshakelford]

I do not think you are stupid, I agree with everything you said. I too prefer deep gears in my vehicles. I am currently running 5.13's In a JLUR 6 speed with 35's. With two overdrive gears in Jeeps JLs they are still easy to drive on the interstate even with 5.13's. Why not consider 5.38's? cause you know your going to run 37's someday, maybe even 40's, plus gears make for a great foundation for other mods.

This is the direction we are going when our Jeep comes in. 5.13 on 37s with the 6 speed. I’m thinking it’ll like the slightly higher rpms on the highway too. When we test drove one, it felt almost like you were lugging it at 70

I typically don’t drive faster than 65 so hopefully it’ll be a good fit

Brett

 

[Carlton]

Tall gears = numerically low numbers such as 3.05 3.21, 3.45 etc

Short gears = numerically high numbers such as 4.88, 5.13, 5.38 etc

The lower the number the taller the gear. The higher the number the shorter the gear.

 

[Solidaxle]

The lower the gear ratio the smaller the pinion the weaker it is.
There is a huge strength difference between a 4.10 ratio and a 5.38 ratio in a Dana 30 to 44-ish type of configuration on a dana 80 it’s OK.

 

[DesertsJL]

Maybe I referred to a taller gear when I should have referred to a shorter gear, or vis versa. I think that it was easy enough for anybody to read and get where I was going.

After having run the 5.38’s with the 8-speed auto now for a couple months, I wouldn’t go back. At first they gears felt a little tall (or short, lol), but I easily became accustomed to them. It’s pretty hilly around here and on the highway the Jeep motors along without hunting between 6-8 speeds. Engine runs right around 3000rpm at 80mph.

I’ll likely get 37’s next time around.

 

[Bravo]

Just picked up a Rubi Unlimited... 3.6 with the six speed. I'm trying to decide between 5.13's or 5.38's with 37's...

 

[DrowningTurtle]

I'm also trying to decide between 4.88 or 5.13s with 37s

 

[rustyshakelford]

Just picked up a Rubi Unlimited... 3.6 with the six speed. I'm trying to decide between 5.13's or 5.38's with 37's...

I'm also trying to decide between 4.88 or 5.13s with 37s

Kinda late to this but we just ordered 5.13 to go with our 37s. After doing the math, it’ll make 6th gear much more usable for highway driving. Should be better Offroad too.

Brett

 

[mickey3]

Kinda late to this but we just ordered 5.13 to go with our 37s. After doing the math, it’ll make 6th gear much more usable for highway driving. Should be better Offroad too.

Brett

Good for you. Let us know what you think of the new gears.

 

[Leadfoot]

Kinda late to this but we just ordered 5.13 to go with our 37s. After doing the math, it’ll make 6th gear much more usable for highway driving. Should be better Offroad too.

Brett

Brett, I am looking to do the same thing and I am having a hard time deciding between 4.88 or 5.13 gears. How are the 5.13 gears and would you stay with them or possible consider the 4.88 gears? Is 1st gear a pain? How does it cruise on the interstate ?

 

[rustyshakelford]

Brett, I am looking to do the same thing and I am having a hard time deciding between 4.88 or 5.13 gears. How are the 5.13 gears and would you stay with them or possible consider the 4.88 gears? Is 1st gear a pain? How does it cruise on the interstate ?

Well after having them I’m slightly conflicted on it. The math said my rpms should be lower than they are. At 70 I’m turning 2500. I was anticipating around 2300. First gear is great, I shift out around 10 mph and do nearly every shift before 3000. Mileage is hovering around 15-16. The more highway the less it would be. I tend to drive like I’m 94 vs 34 and prefer 60-65 max. That helps mileage out a ton. There is plenty of power in 6th now. If you do extensive highway and like to drive 75-80 you’ll love the power but I think the mileage hit will suffer. I daily drive my Dually and take my son back and forth to school in the Jeep so the hit on gas isn’t a large concern for our situation. I love 1st and don’t understand th guys that say it’s to tall. Any truck has a gear like that. I guess it’s sports cars that can really rap out first but I’ve never had one

Brett

 

[OffRoadWarehouse]

Here's a monkey wrench for everyone.

Going with a higher numeric gear ratio almost always sacrifices the pinion head size and tooth count in order to achieve the correct numerical ratio. This means that you are sacrificing the strength of the gears (less teeth grabbing means less surface area for force to be transmitted) in order to get the higher RPM's.

So side by side, with the same driver and comparable vehicles, a 5.13 or above is much more likely to shear than a 4.88 and below.

 

[Zeus]

We saw that problem with the FJ Cruisers... 4.88s would fail before 4.56 or even OE. However, I wonder how much meat you are giving up on the 44? Is the pinion head that much smaller with the lower (higher) gears? So much so that you are giving up actual durability?

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