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3.73, 4.27 & 4.46 ratio on-road?

Beachin 74

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Nobody ever said "I'm glad I got the 3.31's instead of the 3'73's".
When folks pay a couple grand to re gear they always go for more low end grunt.
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JT1

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Which is about 3500-4000 rpm higher than where a 460 in a f150 on 35"s will comfortably cruise on the highway.

Which was my point.
The new engines require us to rethink rear end gearing towards deeper sets.
Big blocks are an entirely different animal. And the 460 didn't need gearing to help it.

On the 3.6 v6 in new jeeps, 4.88 and 5.13 are the common gear sets for 37" tires depending on manual or automatic. Both of the bronco engines have better power than the 3.6, so I can't imagine a use case where you would need deeper than 5.13s for a 37.
 

PRA4SNW

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Thought that I would post my question here instead of starting a new thread.
Here's my build:
Big Bend, 2.3 Auto, stock wheels and tires with no plan on upgrading soon, mostly highway driving.
Is there any benefit to the 4.27 axle ratio other than locking rear?
Will mileage be affected?
 

kodiakisland

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Always go low, unless you like to go slow.
 

PRA4SNW

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kodiakisland

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So, 4.27 is slower than 3.73?
I'm new to all of this.

Well, yes and no. 4.27 is a lower gear, but it will give you more low end acceleration and less top end. The 3.73 with bigger tires (or lower HP motor) will be a poorer performing vehicle in everything except top end mpg compared to the 4.27 or lower. My general rule is always go low. I tend to spend more time below interstate speeds and prefer the lowest gears I can get.

With modern transmissions there is little advantage to high gears. Back in the day when overdrives were not universal, it was a bigger deal, but both the auto and MT offer a great range and will handle the low gears on the interstate just fine.
 

The Pope

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And just to help clear up any confusion that some may have.....

The Higher number (4.70 vs. 3.75) is the Lower Gear. (4.70 is a Lower Gear than 3.75)
Yes, it sesames backwards, but that's the way it is.

There is ALWAS a TRADE-OFF when selecting a gear.
With all things equal (tire size/vehicle size & weight)
-The Lower Gear (say 4.70) will give you better acceleration and it will reduce your top end speed along with the engine's RPM being higher than if you had a Taller Gear for say going 65 MPH.
-The Taller Gear (say 3.75) will not be as good at acceleration and it will increase your top end speed along with the engine's RPM being lower than if you had a Lower Gear for say going 65 MPH.

So.... what's more important to you? 0-60 time or top speed?

A better question you might want to ask yourself is...... What RPM do I want to cruse at during my normal commute? Well to answer that, you've got to know which engine & transmission your getting and where the "Sweet Spot" (RPM) the engine likes to operate at.

Picking a gear ratio isn't a simple thing. One that works great for one person can be the worst for someone else.

Hopefully I haven't caused more confusion. If so, I do apologize.
 

RockEye

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For example, my '69 Camaro had a 2 speed powerglide with 4.88 rear. It got up to speed very fast. But it would top out at about 120 mph max due to gearing. And RPM on the highway was about 3 grand or so.

This is a non-issue with a 10 speed auto.
 

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And just to help clear up any confusion that some may have.....

The Higher number (4.70 vs. 3.75) is the Lower Gear. (4.70 is a Lower Gear than 3.75)
Yes, it sesames backwards, but that's the way it is.
Thing people forget(or don’t know) is axles are a RATIO not just a number, so that’s what makes the bigger number a lower gear. There’s always a :1 that’s implied and typically left off for ease, that’s what makes the lower gears bigger numbers. It’s math.It’s really just inverted fractions, 1/3, 1/4, 1/5. So 3.73 gears is 1/3.73, 4.7 gears are 1/4.7.

Or make it out of 100 to understand the bigger number equals lower gear thing. 3:1 would be 33 out of 100(1/3), 4:1 would be 25 out of 100(1/4), 5:1 is 20 out of 100(1/5). So the bigger number gear makes it actually smaller.
 

EvlNvrDys

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So to add to the mix (and keep it all in one place), this goes out to @kodiakisland (Who's answered gearing questions for me before) @Incognito & @The Pope . If I missed another gear expert, I apologize.

First off to not confuse the class, when you guys say you lose top speed. Ok, so now the Bronco won't do 110, it will do 108? Something like that correct? Would hate to think that I'd be going from doing 80 @ say 2500 RPM, over to going 80 @ 4500 RPM with lower gears. I don't think that's the case, would assume it's more the can't do 110 anymore, now only 108 seems, logical with that statement.

Secondly, my big thing was always towing. Wife's Jeep with the 3.23's (I believe) no good for towing. So for the hell of it, assume I upgrade the 3.73's to 4.46's (staying 33" or smaller tire), it helps greatly? I believe that is what @kodiakisland answered for me before. But a more involved explanation in this thread could certainly help the class even more when deciding.

For the record, I'm either a Base Squatch, or BB (4.27)/BD (4.46 axle) with 33's. V6 + Auto. So either way I feel I'll be good for towing.

Thanks in advance.

Edit: Side Note... I come from FSB's with 5.8's in them. Never used to worry about gearing until just recently.
 
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lsustang05

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My primary goal is fun to drive, acceleration with comfort. MPG is not really a concern. I currently get 12 mpg

Thanks for the help!
Then get the tallest gear possible from the factory. I’m assuming money isn’t a concern for the Bronco with the MPG comment so that’s why I’m saying just get the tallest possible.
 
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lsustang05

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First off to not confuse the class, when you guys say you lose top speed. Ok, so now the Bronco won't do 110, it will do 108? Something like that correct? Would hate to think that I'd be going from doing 80 @ say 2500 RPM, over to going 80 @ 4500 RPM with lower gears. I don't think that's the case, would assume it's more the can't do 110 anymore, now only 108 seems, logical with that statement.

You are correct in that it lowers the top speed AND will increase RPM’s for any given speed when you go to a taller gear. A jump from 2500rpm to 4500rpm will not be the case. I haven’t poured over the gear calculators, but you might see a jump from lets say 2500rpm to 2700rpm. It will be a minimal, although it will be noticeable if you’re looking, increase in RPM’s.

Secondly, my big thing was always towing. Wife's Jeep with the 3.23's (I believe) no good for towing. So for the hell of it, assume I upgrade the 3.73's to 4.46's (staying 33" or smaller tire), it helps greatly? I believe that is what @kodiakisland answered for me before. But a more involved explanation in this thread could certainly help the class even more when deciding.
A taller gear most definitely helps with towing. Going from 3.23’s to 4.46’s would be a massive increase and you should notice that your load gets moving faster and the vehicle doesn’t feel like it’s straining as much. This is also going to be helped by the fact you’ll have a 10 speed transmission and 2 extra gears over the Jeep (assuming you have the 8 speed).
 

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You are correct in that it lowers the top speed AND will increase RPM’s for any given speed when you go to a taller gear. A jump from 2500rpm to 4500rpm will not be the case. I haven’t poured over the gear calculators, but you might see a jump from lets say 2500rpm to 2700rpm. It will be a minimal, although it will be noticeable if you’re looking, increase in RPM’s.


A taller gear most definitely helps with towing. Going from 3.23’s to 4.46’s would be a massive increase and you should notice that your load gets moving faster and the vehicle doesn’t feel like it’s straining as much. This is also going to be helped by the fact you’ll have a 10 speed transmission and 2 extra gears over the Jeep (assuming you have the 8 speed).
It's a 2017 JKU. V6. From what I looked up, appears to be a 6 speed auto, 5 + Overdrive. And it struggles with a 12' trailer and some weight on it. Figure typical tow is around 1700 pounds (trailer) and about 1100 pounds (2 quads or quad + log splitter). So at or near 3000 pounds. I am looking for the Bronco to tow the 3500 (rated) pounds with ease, and definitely opting for the lower gears.
 

Economisto

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So for my setup, from what I understand so far, get a Badlands on 33 with the 4.7 since I plan to do 35s on my own, and I should be good switching between sizes 33 and 35 regularly, and shouldn't have an issue cruising 90mph on the freeway. Correct?
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