6 speed with 37s on a rubicon

ChattVol

Well-Known Member
Joined
Jun 29, 2018
Messages
2,308
Reaction score
2,235
Location
Chattanooga, TN
Vehicle(s)
JLU 6 Speed, 2016 Odyssey, 2014 Accord
Build Thread
Link
Please keep us posted. This is what I'm planning to do as well. Currently stock motor, 6 speed, 37s. Great MPGs in town (18-19MPG), poor on the highway (80+mph, 15-16.5MPG) because 6th is so high. It takes a lot of work to drive it on the highway, especially for me going between 5200 to 7300 ft of elevation on my commute. I worry about the stock clutch handing a power adder.
Have you regeared to accommodate 37s and driving at higher elevation?





Advertisement

 

alphalife9

Well-Known Member
First Name
David
Joined
Nov 6, 2017
Messages
366
Reaction score
176
Location
Rio Rancho, NM
Vehicle(s)
Z51 C6, Sting Gray JLUR
Have you regeared to accommodate 37s and driving at higher elevation?
no this is stock 4.10s. Gears are not required for 37s just nice to have if you want to maintain steady highway speeds in 6th gear. Steep inclines I have to downshift to 3rd to stay over 70MPH but it'll do over 90MPH on the steep incline when I do. It's basically just a lot more work to drive fast but doable. In town its great, no wind resistance means great MPGs.
 

ChattVol

Well-Known Member
Joined
Jun 29, 2018
Messages
2,308
Reaction score
2,235
Location
Chattanooga, TN
Vehicle(s)
JLU 6 Speed, 2016 Odyssey, 2014 Accord
Build Thread
Link
no this is stock 4.10s. Gears are not required for 37s just nice to have if you want to maintain steady highway speeds in 6th gear. Steep inclines I have to downshift to 3rd to stay over 70MPH but it'll do over 90MPH on the steep incline when I do. It's basically just a lot more work to drive fast but doable. In town its great, no wind resistance means great MPGs.
You're driving a box on wheels on 37s and are driving 80-90mph....obviously MPG is gonna be poor. If you care about hwy MPG, running 37s makes zero sense.

Regearing isn't "required" running 37s at high elevations if you like a useless 6th gear, barely useable 5th and have to be in 3rd to hold 70mph on inclines. It's making the transmission work harder bc your gears aren't setup to properly utilize the powerband. You're low end power/crawling is also going to be sub optimal.

I bet regearing to 5.13 would make it feel like a new jeep. Makes alot more sense to regear driving on 37s at high elevations vs. spending $2k(with labor) on an aftermarket clutch if the stock clutch is working fine.
 

alphalife9

Well-Known Member
First Name
David
Joined
Nov 6, 2017
Messages
366
Reaction score
176
Location
Rio Rancho, NM
Vehicle(s)
Z51 C6, Sting Gray JLUR
You're driving a box on wheels on 37s and are driving 80-90mph....obviously MPG is gonna be poor. If you care about hwy MPG, running 37s makes zero sense.

Regearing isn't "required" running 37s at high elevations if you like a useless 6th gear, barely useable 5th and have to be in 3rd to hold 70mph on inclines. It's making the transmission work harder bc your gears aren't setup to properly utilize the powerband. You're low end power/crawling is also going to be sub optimal.

I bet regearing to 5.13 would make it feel like a new jeep. Makes alot more sense to regear driving on 37s at high elevations vs. spending $2k(with labor) on an aftermarket clutch if the stock clutch is working fine.
MPGs are going to be poor going 85-95MPH no matter what. Gears aren't going to magically lower the coefficient of friction of a giant square box. If I cared about MPGs I would just take my time or drive something else during my commute but I enjoy driving my Jeep.

There is a severely steep incline just before Santa Fe on I-25N where you can often see tractor trailers doing about 45MPH. That's the only place I downshift to 3rd and I can hold 90MPH no problem if I do.

It actually holds 70MPH when its fairly flat in 6th gear and gets 17+MPG but the speed limit is 75 and my way to work is mostly uphill so going slow only happens when I'm not going to work. Around town I can easily get 18.5MPG and have no problems with acceleration. I actually surprise a lot of cars off the line.

I rock crawl all the time and it does amazingly in 4 Low so no that's not even remotely an issue

Maybe you misunderstood, I want to get an aftermarket clutch when I get a power adder or engine swap. The factory clutch is perfectly suited for the factory power level. I want to get a power adder or an engine swap only cause I'm used to really fast vehicles so that's just what I like. When I do that I'll probably need a clutch that can handle more torque than the factory unit.

One key point to remember is that 5.13s has smaller teeth (weaker) than the factory 4.10s. I don't mind having to shift more often on the highway if I can maintain greater reliability when I am bumping over large rocks. I chose a 6 speed only because I like to shift, not because I thought it was better than the new 8 speed nor because of the price difference.

I will admit around 8000+ ft elevation in CO the Jeep started feeling like a dog but where I am its fine.
 

ChattVol

Well-Known Member
Joined
Jun 29, 2018
Messages
2,308
Reaction score
2,235
Location
Chattanooga, TN
Vehicle(s)
JLU 6 Speed, 2016 Odyssey, 2014 Accord
Build Thread
Link
MPGs are going to be poor going 85-95MPH no matter what. Gears aren't going to magically lower the coefficient of friction of a giant square box. If I cared about MPGs I would just take my time or drive something else during my commute but I enjoy driving my Jeep.

There is a severely steep incline just before Santa Fe on I-25N where you can often see tractor trailers doing about 45MPH. That's the only place I downshift to 3rd and I can hold 90MPH no problem if I do.

It actually holds 70MPH when its fairly flat in 6th gear and gets 17+MPG but the speed limit is 75 and my way to work is mostly uphill so going slow only happens when I'm not going to work. Around town I can easily get 18.5MPG and have no problems with acceleration. I actually surprise a lot of cars off the line.

I rock crawl all the time and it does amazingly in 4 Low so no that's not even remotely an issue

Maybe you misunderstood, I want to get an aftermarket clutch when I get a power adder or engine swap. The factory clutch is perfectly suited for the factory power level. I want to get a power adder or an engine swap only cause I'm used to really fast vehicles so that's just what I like. When I do that I'll probably need a clutch that can handle more torque than the factory unit.

One key point to remember is that 5.13s has smaller teeth (weaker) than the factory 4.10s. I don't mind having to shift more often on the highway if I can maintain greater reliability when I am bumping over large rocks. I chose a 6 speed only because I like to shift, not because I thought it was better than the new 8 speed nor because of the price difference.

I will admit around 8000+ ft elevation in CO the Jeep started feeling like a dog but where I am its fine.
I was responding to your post above asking about the aftermarket clutch and claiming your jeep takes alot of work to drive on the hwy and was getting poor mpg(15-16) driving 80+mph on 37s at 5000-7000 ft.(15-16mpg driving 80+mph on 37s isnt bad in a jeep on 37s IMHO)

I have a 6 speed on 37s and stock 4.10s...6th gear is useless for me and only holds 70mph on hwy downhills at low elevation. Adding power would obviously help depending on what you're adding, but you're still running 37s at high elevation on gears setup for 33s. Look at folks swapping in hemi's and superchargers, none that I see are running 4:10 gears. Regearing to 4.88 or 5.13 makes alot of sense to have proper use of the gears on 37s at high elevations and add back low end power if you wheel the jeep. Just my $.02...Best of luck.:bandit:
 
Last edited:

Toycrusher

Well-Known Member
Joined
Oct 2, 2019
Messages
854
Reaction score
1,070
Location
Texas
Vehicle(s)
JLUR
MPGs are going to be poor going 85-95MPH no matter what. Gears aren't going to magically lower the coefficient of friction of a giant square box. If I cared about MPGs I would just take my time or drive something else during my commute but I enjoy driving my Jeep.

There is a severely steep incline just before Santa Fe on I-25N where you can often see tractor trailers doing about 45MPH. That's the only place I downshift to 3rd and I can hold 90MPH no problem if I do.

It actually holds 70MPH when its fairly flat in 6th gear and gets 17+MPG but the speed limit is 75 and my way to work is mostly uphill so going slow only happens when I'm not going to work. Around town I can easily get 18.5MPG and have no problems with acceleration. I actually surprise a lot of cars off the line.

I rock crawl all the time and it does amazingly in 4 Low so no that's not even remotely an issue

Maybe you misunderstood, I want to get an aftermarket clutch when I get a power adder or engine swap. The factory clutch is perfectly suited for the factory power level. I want to get a power adder or an engine swap only cause I'm used to really fast vehicles so that's just what I like. When I do that I'll probably need a clutch that can handle more torque than the factory unit.

One key point to remember is that 5.13s has smaller teeth (weaker) than the factory 4.10s. I don't mind having to shift more often on the highway if I can maintain greater reliability when I am bumping over large rocks. I chose a 6 speed only because I like to shift, not because I thought it was better than the new 8 speed nor because of the price difference.

I will admit around 8000+ ft elevation in CO the Jeep started feeling like a dog but where I am its fine.
It's definitely more economical to grab a lower gear than to regear axles just so you can say you use 6th. It's also cheaper to shift into low range and use a higher gear for fastest sections than to regear so you can brag about climbing an obstacle in 4hi.

All that being said, nothing wrong with spending your money wherever the heck you want for any desired results you want.

I'm happy with 37s and 4.10 gears, but I am VERY interested in that new clutch and heavier flywheel. How noticeably did the heavier clutch affect acceleration?
 

ChattVol

Well-Known Member
Joined
Jun 29, 2018
Messages
2,308
Reaction score
2,235
Location
Chattanooga, TN
Vehicle(s)
JLU 6 Speed, 2016 Odyssey, 2014 Accord
Build Thread
Link
The new clutch has better feel overall, and out here in AZ we have some trails were you can cruise along at a good clip (4hi) with difficult stretches in between. Before I needed to drop to 4lo as it was to much for 4hi, now with the heavier flywheel it just goes right up and over. In 4lo in the really difficult areas it goes over it really easy.
When I first got my JLR the clutch was the only real disappointment, no feel, to soft, the new Centerforce dual friction is a huge improvement. Knowing I was going to supercharge it as soon as the Maggie became available I had a good feeling that the stock clutch probably wouldn’t last. After comparing the stock and the Centerforce side by side I’m sure it would fail. The cost of it wasn’t bad either, under $1k. Each Centerforce comes with a build sheet and tested to see how much torque it will hold. With holding power of over 600 ft. lbs. of torque I’m pretty confident it will hold up really well. Honestly I was surprised at the stock clutch and it’s design, it’s going to be a weak point long term in the manual JL. Jeeps engineers failed in my opinion, the current unit is focused more for rookie manual drivers whose primary use is street driving. They didn’t focus in on the hard core off road user.
I have several vehicles to choose from daily and I didn’t purchase my JL to daily drive, I wanted a sold off road toy. I find myself using it more as a daily when I’m doing local runs, city driving, since it’s so much nicer to drive since I upgraded the clutch.
I run Centerforce clutches in my race car, CJ and sports cars and they have always been great, I’m pleased that they were proactive and developed an upgrade for the JL right off the bat. I still haven’t seen another option yet.
My post was responding to you saying the new clutch is a gamechanger offroad bc it crawls over everything in 4high and 4low. In 1st gear and 4low, my JL on 35s idles over obstacles with the stock clutch. I don't understand why it's a gamechanger to be able to crawl better in 4hi. When crawling over obstacles, I prefer to be moving slow and controlled. For wheel speed in 4lo, I shift to 2nd or 3rd and give it some skinny pedal.
 

ChattVol

Well-Known Member
Joined
Jun 29, 2018
Messages
2,308
Reaction score
2,235
Location
Chattanooga, TN
Vehicle(s)
JLU 6 Speed, 2016 Odyssey, 2014 Accord
Build Thread
Link
Wow, i have the exact opposite opinion ,Compared to my 03 Rubicon similarly equipped, our 18 Rubicon sucks off road,with no torque ,stalling and having to rev and slip clutch to operate smoothly. I too believe a heavier flywheel will improve its ability .
What size tires are you running?
 

ChattVol

Well-Known Member
Joined
Jun 29, 2018
Messages
2,308
Reaction score
2,235
Location
Chattanooga, TN
Vehicle(s)
JLU 6 Speed, 2016 Odyssey, 2014 Accord
Build Thread
Link
35 with 5:13 gears . the gears helped alot but still needs improvment .
I'm not sure how you're stalling in 1st gear with 5.13 gears if in in 4low. Mine and my friends on 35s idles over obstacles with 4.10s.
 

Brew211

Well-Known Member
First Name
Todd
Joined
Jun 18, 2018
Messages
506
Reaction score
336
Location
Peoria, Arizona
Vehicle(s)
2018 JLUR - Manual, Tundra
Vehicle Showcase
1
Help me understand, I'm running 37's on stock Rubi 4.10's and 4low 1st gear is nearly useless as it rev's so hi. Rock-crawling I typically start in 4low 2nd gear. What will re-gearing to 4.88's or 5.13's do to help me rock crawling?
Thank you,
Brew
 

Az-jewel

Well-Known Member
First Name
Julie
Joined
May 1, 2019
Messages
233
Reaction score
403
Location
Sunny AZ
Vehicle(s)
‘18 JLU Sport S
Build Thread
Link
Occupation
SAHM
Help me understand, I'm running 37's on stock Rubi 4.10's and 4low 1st gear is nearly useless as it rev's so hi. Rock-crawling I typically start in 4low 2nd gear. What will re-gearing to 4.88's or 5.13's do to help me rock crawling?
Thank you,
Brew
I want to know this too? I’m running 35’s and haven’t regeared yet... I stall in 1st gear climbing good size rocks in either 4lo or 4 hi. I have tried both and need to ride the clutch in 1st the keep from stalling.
I noticed it crawls along nicely in neutral in 4hi until it comes to a Little Rock .
whst do you guys do?
 

Toycrusher

Well-Known Member
Joined
Oct 2, 2019
Messages
854
Reaction score
1,070
Location
Texas
Vehicle(s)
JLUR
I want to know this too? I’m running 35’s and haven’t regeared yet... I stall in 1st gear climbing good size rocks in either 4lo or 4 hi. I have tried both and need to ride the clutch in 1st the keep from stalling.
I noticed it crawls along nicely in neutral in 4hi until it comes to a Little Rock .
whst do you guys do?
You are running 3.45 gears and 2.73 transfer case, crawl ratio roughly 38:1, and with 35" tires, your going to have some trouble even in 4-lo.

On a Rubicon, you have 4.10 gears and 4:1 t-case, roughly 70:1 ratio, much easier for the motor to pull you up an incline
 

Advertisement




Hothead Headliners
 



Advertisement
Top