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JL & JLU Wrangler Axle Gear Ratios: 3.45, 3.73, 4.10

DanW

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Folks, the engineers have hard data, and lots of it, to make gearing decisions. Most of it is data to which we are not privy. The JL is much more similar to the JK than the JK was to the TJ, so that gave them a good decade long baseline from which to work. I'm confident they'll create powertrain combinations that work well for the JL.
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Jabs

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I'm new to Jeeps but to make sure I understood correctly and sorry if this is a stupid question.

If I want to get larger tires (35's possibly 37's) I would need to get the 4.10 gears on the Rubicon? What's the difference between lower and higher gears?
 

Bearded_Dragon

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Folks, the engineers have hard data, and lots of it, to make gearing decisions. Most of it is data to which we are not privy. The JL is much more similar to the JK than the JK was to the TJ, so that gave them a good decade long baseline from which to work. I'm confident they'll create powertrain combinations that work well for the JL.
I agree. No doubt some areas can and will be overlooked and aftermarket companies might release an improved part, but that comes after hands on time with the vehicle.
 
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Billy

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I'm new to Jeeps but to make sure I understood correctly and sorry if this is a stupid question.

If I want to get larger tires (35's possibly 37's) I would need to get the 4.10 gears on the Rubicon? What's the difference between lower and higher gears?
For larger tires, yes, larger ring gear, which is a higher number.
 

DanW

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I agree. I have more faith in Jeep than random people on a forum who think they know how to design/engineer a vehicle. No doubt some areas can and will be overlooked and aftermarket companies might release an improved part, but that comes after hands on time with the vehicle.
What I said wasn't a knock on those on this forum that know a great deal about gearing. I was just saying that the engineers can fill in the holes with LOTS of actual data. There are some folks here, Ape in particular, who have offered a clinic on understanding gearing and how it could affect on and off road drivability. I was simply pointing out that the engineers know things that we can only guess about. That said, I would not bet a single dime against Ape in predicting how it turns out. If he's off, it won't be by much, and I'd wager it would be just because of some data piece to which he did not have access.
 
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Jabs

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For larger tires, yes, larger ring gear, which is a higher number.
Glad I learned that now to avoid re-gearing later! Thanks!

Could I fit 37's on the 4.10 gears? What do larger gears do exactly?
 

digitalbliss

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Glad I learned that now to avoid re-gearing later! Thanks!

Could I fit 37's on the 4.10 gears? What do larger gears do exactly?
I'm curious if 4.10s will work with the 8 speed / 3.0L Diesel combo for 37s. I would assume they would be perfect for 35s since 4.88s are perfect for a JK with 35s and the diesel / 8speed seems to be geared down in comparison to the JKU set up.
 

The Great Grape Ape

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@DanW I understand, which is why I took no issue with that. Because realistically like I stressed before, it’s all just guessing after a WTF reaction to seeing the list.

Usually I am the one to say cool your fears or optimism, which is why I mention the big caveat, and my only reason for mentioning my concern was because of JeepsterFreak’s comment got me thinking about the choices or lack therefore and the impact and reasoning.

I would usually just trust in FCA having gone through the wringer, but unfortunately the manual transmission almost seemed like a non-option a year ago, and then an afterthought after that. And equally unfortunate, not everything is within FCA’s control. They don’t design the manual transmissions, so their options are limited to whomever they can source, so until recently the donor candidates seemed like a tough match for the good characteristics of the ZF8, but the ZF S6 series is OK and only recently did the high spread SUV Tremec appear (it wasn’t part of last year’s SUV list/pdf) and it is a perfect fit IMO. So seeing this list has me apprehensive as to the motivation, specially since I want one in my JK->JL replacement.

Again, it’s just thinking out loud, people don’t need to comment on it just come up with their own ideas...
 
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TLife

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I'm new to Jeeps but to make sure I understood correctly and sorry if this is a stupid question.

If I want to get larger tires (35's possibly 37's) I would need to get the 4.10 gears on the Rubicon? What's the difference between lower and higher gears?
This chart, while specifically applicable to the JK NOT THE JL, might help to give a general understanding of how gear ratio relates to tire size.

3.6-jkgearing.jpg
 

TexTJ209

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This was fantastic! Thank you.

After reading through this I'm confident 35's with the 4.10 gears would be a fine fit considering Rubicon comes with 31's or 33's but what about 37's?

Larger tire sizes without changing the gear ratio (to numerically higher) just makes the vehicle more sluggish. It's not a requirement per se, but if you want something similar to your original power levels then you'll need to re-gear. 37s and 4.10s will just require patience at highway speeds...when you finally reach them. :)
 

The Great Grape Ape

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After reading through this I'm confident 35's with the 4.10 gears would be a fine fit considering Rubicon comes with 31's or 33's but what about 37's?
Depends on your expectations. It will still be sluggish compared to smaller, but quite usable.

Remember it’s not just the axles and transmisions that will help, another aspect to remember is engine(s), the improved torque delivery on the Pentastar will help with getup and go as well as providing a meatier sweet spot than before when cruising, and the other two options have the potential of even better get-up an go initially, but we’ll need to see.
 

TLife

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This totally omits engine and transmission from the equation...
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