Sponsored

3.6L, 8 AT, 37”: 4.88 or 5.13?

Chocolate Thunder

Well-Known Member
First Name
Jeremy
Joined
Feb 20, 2018
Threads
221
Messages
5,354
Reaction score
10,450
Location
Texas
Vehicle(s)
2019 Wrangler Unlimited Rubicon
Build Thread
Link
The questions I have for those with 3.6L engine, automatic transmission, and 37” tires:
  • Did you regear to 4.88 or 5.13 gears?
  • Do you regret your choice and wish you’d selected another ratio?
  • What do you like most and least about your new gear ratio?
  • Anything in hindsight that you wish you’d known beforehand?
I care about having 8th gear back on the highway. My off-roading is usually crawling on rocks, not slogging through mud or blasting through the desert over dunes.
Sponsored

 

Coolbaldguy

Well-Known Member
First Name
Tim
Joined
Apr 29, 2019
Threads
3
Messages
83
Reaction score
144
Location
TN
Vehicle(s)
2019 JLR
:movember: Watching with much interest.
 

tjeeper

Well-Known Member
First Name
Patrick
Joined
May 7, 2017
Threads
13
Messages
167
Reaction score
226
Location
Utah
Vehicle(s)
'99 TJ, '24 392
I was about to post a similar post. I have the same specs, want to regear, not sure 4.88s or 5.13s. My main concern is getting 7th and 8th gears back on the highway. Typically I drive 80-85mph. It wouldn't make sense for me to go to 4.88s if I get 7th but not 8th. But if it works with 4.88s, 5.13s would be lower than I want.

I've spent hours looking at posts, the only conclusion I can come up with is people who have regeared are happy with their decision, regardless of 4.88s or 5.13s.

I'm not concerned with off road. Since the tranny defaults to 2nd from a stop in 4lo, I can manually drop down to 1st if needed.
 
OP
OP
Chocolate Thunder

Chocolate Thunder

Well-Known Member
First Name
Jeremy
Joined
Feb 20, 2018
Threads
221
Messages
5,354
Reaction score
10,450
Location
Texas
Vehicle(s)
2019 Wrangler Unlimited Rubicon
Build Thread
Link
Same boat. I don’t typically drive as fast as you do, but I want to see 8th gear consistently at highway cruising speeds. It was rare even with 35s, with the 37s now it’s usually in 6th at highway speed. I tend to think that 5.13 is too much. As far as off-road, I think 4.88 will deliver enough low end torque for the things I do. That’s the way I’m leaning but just asked for the experiences of others to consider.
 

Kurt0

Well-Known Member
First Name
Kurt
Joined
Oct 11, 2020
Threads
34
Messages
794
Reaction score
1,348
Location
Virginia
Vehicle(s)
Gladiator Mojave
Occupation
IG Model and Influencer
(New tire size X factory gear ratio)/factory tire size = new gear ratio for proximation of nominal operation.

so mathematically that would be about 4.56. Id go 4.88 to compensate for the weight of the tire and (what is imo) overly tall 8th gear. 5.13 if you frequently haul or tow heavy.

its just a rule of thumb; you can play around with the gearing calculators to see what you are revving at what speed with what tire/gear size.
 

Sponsored

tjeeper

Well-Known Member
First Name
Patrick
Joined
May 7, 2017
Threads
13
Messages
167
Reaction score
226
Location
Utah
Vehicle(s)
'99 TJ, '24 392
(New tire size X factory gear ratio)/factory tire size = new gear ratio for proximation of nominal operation.

so mathematically that would be about 4.56. Id go 4.88 to compensate for the weight of the tire and (what is imo) overly tall 8th gear. 5.13 if you frequently haul or tow heavy.

its just a rule of thumb; you can play around with the gearing calculators to see what you are revving at what speed with what tire/gear size.
You don't have 37s do you? The gear calculators are theoretical. According to them, I should be turning 2164 rpm in 8th gear at 70mph. The reality is, I can't get into 8th gear unless I am going downhill. My Jeep is in either 6th or 7th, depending on the load on the engine. The faster you go, the power needed to maintain speed increases exponentially.

We are asking people's real world experience. If I put 4.88s in my Jeep, will it be stay in 8th gear at 70mph? How about 80mph?
 

Kurt0

Well-Known Member
First Name
Kurt
Joined
Oct 11, 2020
Threads
34
Messages
794
Reaction score
1,348
Location
Virginia
Vehicle(s)
Gladiator Mojave
Occupation
IG Model and Influencer
You don't have 37s do you? The gear calculators are theoretical. According to them, I should be turning 2164 rpm in 8th gear at 70mph. The reality is, I can't get into 8th gear unless I am going downhill. My Jeep is in either 6th or 7th, depending on the load on the engine. The faster you go, the power needed to maintain speed increases exponentially.

We are asking people's real world experience. If I put 4.88s in my Jeep, will it be stay in 8th gear at 70mph? How about 80mph?
calm down, hero. Goodness. Having 37’s isn’t some elite secret society with a handshake and crested ring and password bonafides challenge.

the calculators arent theoretic, and we can use them and math to figure out what works for you. but they are garbage in garbage out. Get on the highway and determine which cog of your transmission behaves the way you want your 8th cog to behave after regear. note the cruising rpm. You can use this trip to get another barbed wire bicep tattoo; or go to the gym and do curls in the squat rack while people waiting to squat watch you. Its cool, because they, like us, know how serious you are.

Next, measure the circumference of your tire and determine the exact revs per mile of your tire at your inflation.

load the transmissions specs into the gearing calculator and use the revs per mile figure you calculated, and use the cog specs to calculate the active final drive and regear to that. Or enter in new final drive gear options until you see 8th cog reflect the rpm you were turning on the highway test. If staying in 8th cog is your top priority, this is the only way to make sure you get the gearing that will do that based on your jeep, area, and driving style. Given your priority for 8th cog, I’d guess 5.13 is where youll come out.

if thats too time consuming; drop on the passenger tires from a Sahara and regear to 5.33. i can guarantee you’ll stay in 8th Cog. Otherwise,

happy jeeping.
 
Last edited:

TxJeepers

Well-Known Member
Joined
Nov 20, 2017
Threads
99
Messages
1,058
Reaction score
1,239
Location
USA
Vehicle(s)
2022 JLUR XR
Couldn’t be happier with 5.13 and have multiple posts on another thread about it. If you are in Austin area I’ll let you drive it.
 
OP
OP
Chocolate Thunder

Chocolate Thunder

Well-Known Member
First Name
Jeremy
Joined
Feb 20, 2018
Threads
221
Messages
5,354
Reaction score
10,450
Location
Texas
Vehicle(s)
2019 Wrangler Unlimited Rubicon
Build Thread
Link
Please keep it civil guys, I hope that this thread can be useful to me any anyone else with the same situation. All of the information and opinions presented so far have been helpful for me. Thanks.
 

chris4prez

Well-Known Member
First Name
Chris
Joined
Sep 14, 2019
Threads
20
Messages
134
Reaction score
57
Location
Tampa
Vehicle(s)
'20 JLUR
5.13 here and I love them with my heavier build. I was on the fence for 4.88 or 5.13 but after all the threads on 5.13 here I was sold to make the jump and glad I did. Got 8th back, better pickup, and just feels smoother overall.

Build: JLUR, beadlock 37s, UD44 in front, chromoloy axel shafts in rear, rhino rack, rockslide side steps w/ armor, steer smarts setup, 2.5 Rock Krawler xfactor with fox dual res shocks.
 

Sponsored

AUJL

Member
First Name
Justin
Joined
Jan 14, 2020
Threads
1
Messages
22
Reaction score
95
Location
Franklin, TN
Vehicle(s)
18 JLUR
The questions I have for those with 3.6L engine, automatic transmission, and 37” tires:
  • Did you regear to 4.88 or 5.13 gears?
  • Do you regret your choice and wish you’d selected another ratio?
  • What do you like most and least about your new gear ratio?
  • Anything in hindsight that you wish you’d known beforehand?
I care about having 8th gear back on the highway. My off-roading is usually crawling on rocks, not slogging through mud or blasting through the desert over dunes.
I'm about 6 months in on 4.88's and have no regrets. It feels similar to stock, I didn't wait too long after going to 37's to regear. 8th gear is back completely, will drop into 7th on the interstate going up hills if necessary similar to stock.
 
Last edited:

4xFUN

Well-Known Member
First Name
Mike
Joined
Dec 9, 2019
Threads
50
Messages
1,432
Reaction score
2,268
Location
Scottsdale AZ
Vehicle(s)
2020 2-door Rubi. 2023 RAM TRX
Just ordered 4.88's...I am running 35" KO2's on a 3.6 JLR with stock 4.10's and rarely if ever see 8th, even on flat hi-ways. (Yes, I had the dealer calibrate for 35's right after install) I told myself 35's were as big as I would ever go...Now I plan to go with 37" KO2's as soon as the new load range C (developed for the new Ford Raptor) are available-hopefully end of April or early May.

Silly me, when I first ordered my JLR I thought 33's would be fine...Before she even arrived I had bought her a set of 35" KO2's. Fast forward one year and she's getting 37's, 4.88's, chromoly axles...However, I am blaming this latest upgrade bug on Jeep corporate for definitely telling the GM at my dealer that they are not making a 2-door V8!

My 2 cents:
For those with JLUR's running heavier tires and wheels or those who might someday jump to 38's or 39's, 5.13's would probably be a better choice.
 

word302

Well-Known Member
Joined
Sep 13, 2017
Threads
11
Messages
5,146
Reaction score
5,718
Location
Oregon
Vehicle(s)
JLU
(New tire size X factory gear ratio)/factory tire size = new gear ratio for proximation of nominal operation.

so mathematically that would be about 4.56. Id go 4.88 to compensate for the weight of the tire and (what is imo) overly tall 8th gear. 5.13 if you frequently haul or tow heavy.

its just a rule of thumb; you can play around with the gearing calculators to see what you are revving at what speed with what tire/gear size.
This doesn’t account for the rolling mass of the new tires though. Unless you have unlimited torque it makes a big difference. I would go 5:13 with 37s for that reason.
 

Kurt0

Well-Known Member
First Name
Kurt
Joined
Oct 11, 2020
Threads
34
Messages
794
Reaction score
1,348
Location
Virginia
Vehicle(s)
Gladiator Mojave
Occupation
IG Model and Influencer
This doesn’t account for the rolling mass of the new tires though. Unless you have unlimited torque it makes a big difference. I would go 5:13 with 37s for that reason.
😐😐
(New tire size X factory gear ratio)/factory tire size = new gear ratio for proximation of nominal operation.

so mathematically that would be about 4.56. Id go 4.88 to compensate for the weight of the tire and (what is imo) overly tall 8th gear. 5.13 if you frequently haul or tow heavy.

its just a rule of thumb; you can play around with the gearing calculators to see what you are revving at what speed with what tire/gear size.
37/4.88 is working out fine for me so far. Holds interstate speed just fine, accelerates from a stop more easily, still reasonably efficient, etc. If I was planning on doing lots of camper towing, I'd have gone 5.13 or 5.38.
Sponsored

 
Last edited:
 



Top