Why not 4.10 gears with 37’s on the 392?

texasbryan

Well-Known Member
First Name
Bryan
Joined
Feb 24, 2018
Messages
236
Reaction score
144
Location
Texas
Vehicle(s)
2021 JLUR 392; 2018 JLUR (sold); 2016 JKU (sold)
Using some back of the napkin math tells me that 4.18 gears with 37 inch tires would be equivalent to the 392 stock configuration of 3.73 gears with 33 inch tires.

Since 4.18 gears are not a thing...4.10 would be the closest.

So...why do most people tend to lean towards 4.56 or 4.88?

I am assuming for greater acceleration and rock crawling at the expense of higher RPMs at highway speeds and reduced fuel economy?

I ask because I am planning to re-gear at some point soon and want to make an informed decision.

I appreciate any input.
Advertisement

 
Last edited:

Some Random Guy

Well-Known Member
Joined
Sep 16, 2020
Messages
633
Reaction score
822
Location
Washington
Vehicle(s)
2020 JLUR, 2018 Subaru BRZ
Build Thread
Link
Occupation
Comptroller
Using some back of the napkin math tells me that 4.18 gears with 37 inch tires would be equivalent to the stock configuration of 3.73 gears with 33 inch tires.

Since 4.18 gears are not a thing...4.10 would be the closest.

So...why do most people tend to lean towards 4.56 or 4.88?

I am assuming for greater acceleration and rock crawling at the expense of higher RPMs at highway speeds and reduced fuel economy?

I ask because I am planning to re-gear at some point soon and want to make an informed decision.

I appreciate any input.
Yep, you nailed it.
The auto drivers are usually trying to get 8th gear back at their normal highway RPM. I think most have the 3.6L so they probably meed more RPM to hold a gear. The 392 may not need the help.
 

AcesandEights

Well-Known Member
First Name
Aces
Joined
Aug 19, 2021
Messages
530
Reaction score
969
Location
So. Oregon
Vehicle(s)
2021 Jeep Rubicon 2D
Taller wheels and tires are also heavier, so there is the additional rotating mass, rolling resistance, etc. Tires are like a big "gear", and the final gear in the whole drivetrain. So, by going larger you're putting a larger gear on the end that is harder to get turning. So...if you're going to re-gear, gear it a little lower to get that larger gear on the end of the equation moving, and staying moving.

You've got rotating parts in the engine connected to gears in the trans that go through gears in the t-case that turn gears in the differentials that turn gears on the end of the axle shafts (tires). They all have to work to turn those last gears (tires).

Ultimately though, you answered your own question.
 

Suffolklou

Well-Known Member
First Name
Lou
Joined
Dec 3, 2019
Messages
533
Reaction score
863
Location
Richland Wa
Vehicle(s)
2020 JLUR
My Rubicon came with 33's and 4.10 gears. I am closer to 4.56 with my 37"s to get back to 8th gear. I cant see spending the money for such a small difference. I am considering going 4.88 though. If I had 3.73's I would have already done it.
 

SSWIM

Well-Known Member
First Name
Sam
Joined
Jun 24, 2020
Messages
352
Reaction score
710
Location
Colorado
Vehicle(s)
Too Many
Really is not worth the cost to only go 4:10s. Not that much different. Especially with the 392. 4:56 would be the enough to justify. My opinion anyway.


Sam
 

MattT69

Well-Known Member
First Name
Matthew
Joined
Jan 2, 2021
Messages
156
Reaction score
473
Location
Arizona
Vehicle(s)
Jeep Wrangler JL Rubicon
Vehicle Showcase
1
4.10 gears works great with 37s assuming you have the right engine and the 37s are not too heavy. I opted for the lightest 37" w/load D-rated tires. At a weight of 69lbs the BFG KO2 weight about the same as some 35s and less than most 37s which can be closer to 80lbs each. As far as engines its good that Jeep finally gave us some options. Based on my experience with my 2 door JLR the i4-2L turbo is awesome at pushing the bigger tires on and offroad and still get 20mpgs. Not sure how it would be with the extra weight of the 4 door on 37s. I think that's where the v8 is the best option or the 4xe with its torque. IMHO
 
Last edited:

MSparks909

Well-Known Member
First Name
Miles
Joined
May 6, 2021
Messages
235
Reaction score
330
Location
NC
Vehicle(s)
JLU Rubicon 3.0
Considering the 392XR is coming stock with 4.56s and lightweight “35s” I wouldn’t stress over installing 4.56s for use with 37s. As Sam said, the $ cost to jump to 4.10s isn’t worth it for the performance gain. The jump to 4.56s would be worth it. Don’t fear the gear!
 

supermike

Well-Known Member
First Name
mike
Joined
Sep 14, 2018
Messages
554
Reaction score
834
Location
Irvine CA
Vehicle(s)
18 JLUR 6 speed 2021 JLUR 392
Ain’t higher the ratio weaker/smaller/finer the ring & pinion gear? Plus the torque of the v8 and leverage of 37 in tire, easier to break a teeth?
 

MSparks909

Well-Known Member
First Name
Miles
Joined
May 6, 2021
Messages
235
Reaction score
330
Location
NC
Vehicle(s)
JLU Rubicon 3.0
Ain’t higher the ratio weaker/smaller/finer the ring & pinion gear? Plus the torque of the v8 and leverage of 37 in tire, easier to break a teeth?
Yes, but that really only applies when you get up to 5.13s on the Dana 44s. 4.88s are strong enough for *moderate* wheeling and 37s with the D44. RCV’s up front and chromoly rear shafts would be a wise choice if you’re actually going to wheel your 392. Again, Jeep is putting 4.56s in these factory now so I see zero reason to only re-gear to 4.10s.

Note: Moderate wheeling implies that you’re not standing on the skinny pedal in your 392 going up obstacles 🤣
 

Brosef

Well-Known Member
First Name
Michael
Joined
Jan 28, 2019
Messages
140
Reaction score
222
Location
Chicago
Vehicle(s)
JL 392
I went with 4.56's and had 37's put on at the same time. feels exactly the same as stock with the 33's. agreed with what's been said in this thread - the added rolling mass of 37's is worth going a touch higher, and 4.10's aren't a big enough difference to be worth the expense of regearing.

Ain’t higher the ratio weaker/smaller/finer the ring & pinion gear? Plus the torque of the v8 and leverage of 37 in tire, easier to break a teeth?
is the ring/pinion the weak point in the axle that would fail (even with shorter gears)? I am curious if teeth count on the pinion gear is overrated as an issue - isn't what matters the number of teeth the force is spread between at any point in time? I'd be interested to see if there's real science to support that there's greater contact among more teeth with taller gear. haven't seen any hard evidence/research on this, so genuinely curious and don't know the answer.
 

alksion

Well-Known Member
First Name
Josiah
Joined
Jan 3, 2021
Messages
1,834
Reaction score
2,204
Location
Brea, CA
Vehicle(s)
21 Rubicon 392, 21 Sahara Altitude
Occupation
Biz Owner
Not numbers based but I drove the whole weekend stock when I purchased it. Then drove back from AZ to CA stock. I put on the 37 BFG K02 C Load tires and I can’t tell a difference at all.

I’m actually shocked how good they look and the Jeep still feels stock to me. Acceleration and gear hunting feel unchanged from the stock BFG 33s. Yes, I know these are smaller and lighter 37s, but they are perfect for my current needs.

Another strange thing. I haven’t installed my tazer mini yet. Waiting for the first oil change. I checked Waze yesterday on the freeway and the speed was the same on the Jeep as it was in Waze. Is this possible?

71233CB1-7262-4ADB-9A75-F84019123B87.jpeg


B7ACA654-3241-489D-B86E-2151767A337A.jpeg


A7407C23-BC21-4C8B-B543-4097D5E80D37.jpeg
 

gato

Well-Known Member
Joined
Apr 4, 2021
Messages
622
Reaction score
766
Location
New England
Vehicle(s)
2021 JLUR
Not numbers based but I drove the whole weekend stock when I purchased it. Then drove back from AZ to CA stock. I put on the 37 BFG K02 C Load tires and I can’t tell a difference at all.

I’m actually shocked how good they look and the Jeep still feels stock to me. Acceleration and gear hunting feel unchanged from the stock BFG 33s. Yes, I know these are smaller and lighter 37s, but they are perfect for my current needs.

Another strange thing. I haven’t installed my tazer mini yet. Waiting for the first oil change. I checked Waze yesterday on the freeway and the speed was the same on the Jeep as it was in Waze. Is this possible?

71233CB1-7262-4ADB-9A75-F84019123B87.jpeg


B7ACA654-3241-489D-B86E-2151767A337A.jpeg


A7407C23-BC21-4C8B-B543-4097D5E80D37.jpeg
Great looking Jeep. I didn't know you had gotten it already. Congrats.

Re your question on speedometer. If you plug in any phone navigation app, like Waze, the Jeep will take the apps GPS speed and display that at the vehicle's speed.

For you to see what the difference is, you have to unplug your phone and look at the Waze's speed while unplugged and compare to the vehicle's speedometer.

I put 37 KO2 and at 28-30PSI I had to set up the Tazer tire size to 36" to get the correct calibration. Hope that helps.

Congrats again.
 

2nd 392

Well-Known Member
First Name
Mike
Joined
Jun 20, 2021
Messages
414
Reaction score
539
Location
Ca
Vehicle(s)
Grand Cherokee srt.V10 Dodge 4x
There’s a chart posted many pages back in the tires thread showing gears-tire size to RPM. 373’s with 33’s was comparable to 410’s with 36’s and 456’s with 39’s. Compensate for weight and mass tells me 410’s for 35’s , 456’s for 37’s
 

alksion

Well-Known Member
First Name
Josiah
Joined
Jan 3, 2021
Messages
1,834
Reaction score
2,204
Location
Brea, CA
Vehicle(s)
21 Rubicon 392, 21 Sahara Altitude
Occupation
Biz Owner
Great looking Jeep. I didn't know you had gotten it already. Congrats.

Re your question on speedometer. If you plug in any phone navigation app, like Waze, the Jeep will take the apps GPS speed and display that at the vehicle's speed.

For you to see what the difference is, you have to unplug your phone and look at the Waze's speed while unplugged and compare to the vehicle's speedometer.

I put 37 KO2 and at 28-30PSI I had to set up the Tazer tire size to 36" to get the correct calibration. Hope that helps.

Congrats again.
Ah I didn’t know that. Makes sense. Thanks for the tip. I’ll try it out today. And thank you. Never new 11.7MPG would ever make me so happy.
 

ozon8r

Well-Known Member
First Name
John
Joined
Mar 31, 2021
Messages
148
Reaction score
175
Location
Denver
Vehicle(s)
2021 392 Hydro Blue
Build Thread
Link
Not numbers based but I drove the whole weekend stock when I purchased it. Then drove back from AZ to CA stock. I put on the 37 BFG K02 C Load tires and I can’t tell a difference at all.

I’m actually shocked how good they look and the Jeep still feels stock to me. Acceleration and gear hunting feel unchanged from the stock BFG 33s. Yes, I know these are smaller and lighter 37s, but they are perfect for my current needs.

Another strange thing. I haven’t installed my tazer mini yet. Waiting for the first oil change. I checked Waze yesterday on the freeway and the speed was the same on the Jeep as it was in Waze. Is this possible?

71233CB1-7262-4ADB-9A75-F84019123B87.jpeg


B7ACA654-3241-489D-B86E-2151767A337A.jpeg


A7407C23-BC21-4C8B-B543-4097D5E80D37.jpeg
I had same issue using waze then realized that when plugged into Apple Play the speed reported in the app is off the speedo and not GPS. I unplugged from Apple Play and the Waze reported speed thru the app and on the iPhone rather than on the Uconnect screen mirrored my GPS enabled radar detector and about 10 MPH different than speedo at 75 MPH reported on Speedo, net net GPS = 85 MPH. This is not a linear relationship and the delta smaller at slower speeds.

Fun fact, any tires larger than OEM will display a lower than actual speed on speedo and thus allow hitting actual speeds beyond the 99 MPH speed limiter since the limiter is tied to speedo which is now inaccurate and slower than actuals unless recalibrated via Taser Mini/AEV module, etc - so I am told and speaking hypothetically :).
 
Last edited:
Advertisement

Motor City Aftermarket
 
Advertisement
Top