Why should I regear?

[Terry R]

So I know there are several threads on regearing, but they mainly centered on what ratio to go with. I want to know the why’s. 2018 JLU Sport S, 3.6, auto, 35x12.5x17 MT Baja Boss AT, 2.5-3” lift(already installed when purchased used).

Why should I spend ~$3000 to regear just because I have 35s and a lift?
Is it just about seeing 8th gear again?
mpg improvement? How much?

Or is there a mechanical/performance reason?

I am not a mechanic nor pretend to be one, so please don’t get to technical.

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[Zandcwhite]

If I were you I'd look for a set of Rubicon take off axles (preferably xr but even the 4.10s will be good for 35s). They can usually be had for about the same price and then you gain stronger/ wider axles, lockers, and gears. If you get a set from a diesel or xr you gain steel knuckles too.

 

[Terry R]

If I were you I'd look for a set of Rubicon take off axles (preferably xr but even the 4.10s will be good for 35s). They can usually be had for about the same price and then you gain stronger/ wider axles, lockers, and gears. If you get a set from a diesel or xr you gain steel knuckles too.

Thanks for the suggestion. I hadn’t thought of Rubi take off axles. Though that doesn’t answer my original questions.

 

[Badunit]

Why should I spend ~$3000 to regear just because I have 35s and a lift?
Is it just about seeing 8th gear again?
mpg improvement? How much?

Opinions vary wildly on whether to spend money on regearing and even more so on what the ideal gearing is. I doubt any regearing will increase your mpg by much, if at all. Going overboard has the potential to reduce it, though.

If your 1st and reverse are sufficiently low now to get you moving over whatever hills and obstacles you traverse at the pace you want to go without struggling, you really don't need to regear. If you want 8th back, a typical ratio for 35's is 4.56 (or 4.88). If you have 3.73 now, going to 4.56 will make 8th roughly the same as what 7th is now. $3K sounds like a lot just to gain one additional gear.

I regeared my JT (with 33's) from 4.10 to 4.56 to get the RPMs up a little higher so it would hold 8th better on interstates and not downshift on every little hill when doing 55-60 mph on highways. 4.88 would have limited my top speed by too much. I expect my interstate mpg will actually be lower on account of this but I haven't driven enough miles to say by how much, plus now it is on winter gas. Was it worth $3K to do this? I don't know. It wasn't a drastic improvement in performance but it has been an improvement. If I don't like it I'll go to 35's and get my overall gearing back to what it was.

 

[Mx5red]

this^
You bought it with bigger tires so you don’t know what to compare it to. Lift doesn’t matter btw.
If you feel like it drives fine then keep it. I don’t know how 35s on sport axles feel but going from 33s to 37s made my JTR feel pretty slow. But it’s not worth my money to regear at this point.

 

[grimmjeeper]

So I know there are several threads on regearing, but they mainly centered on what ratio to go with. I want to know the why’s. 2018 JLU Sport S, 3.6, auto, 35x12.5x17 MT Baja Boss AT, 2.5-3” lift(already installed when purchased used).

Why should I spend ~$3000 to regear just because I have 35s and a lift?
Is it just about seeing 8th gear again?
mpg improvement? How much?

Or is there a mechanical/performance reason?

I am not a mechanic nor pretend to be one, so please don’t get to technical.

Changing the diameter of the tire without compensating with a gear change can affect engine performance and potentially can increase transmission wear.

Also, it improves off road performance.

Some more explanation here:

http://www.grimmjeeper.com/regearing_basics.html

 

[Terry R]

Changing the diameter of the tire without compensating with a gear change can affect engine performance and potentially can increase transmission wear.

Also, it improves off road performance.

Some more explanation here:

http://www.grimmjeeper.com/regearing_basics.html

Thank you for this link. That really helped explain the gearing.

 

[Terry R]

this^
You bought it with bigger tires so you don’t know what to compare it to. Lift doesn’t matter btw.
If you feel like it drives fine then keep it. I don’t know how 35s on sport axles feel but going from 33s to 37s made my JTR feel pretty slow. But it’s not worth my money to regear at this point.

Speed wise mine feels fine. When I get above 65 mph my mpg goes down to around 15 mpg. Country road driving I get around 16.5 mpg. Don’t know if that’s normal for 35s or not.

 

[tomk62]

How do I know what gear I am in any one moment? Is there some screen in the display/dash that can tell me?

 

[GCMWillys]

How do I know what gear I am in any one moment? Is there some screen in the display/dash that can tell me?

You can go into the infotainment settings and update the display to show which gear the Jeep is running. It will show up as a subscript right beside "D."

 

[gm920]

How do I know what gear I am in any one moment? Is there some screen in the display/dash that can tell me?

It's in the EVIC Setup
Screen Setup Driver Selectable Items
Upper Left
 None
 Compass
 Outside Temp
 Time
 Range To Empty
 Average Econ (or L/100km, km/L)
 Current Econ (or L/100km, km/L)
 Trip A Distance
 Trip B Distance
Center
 None
 Compass
 Outside Temp
 Time
 Range to Empty
 Average Econ (or L/100km, km/L)
 Current Econ (or L/100km, km/L)
 Trip A Distance
 Trip B Distance
 Audio
 Menu Title
 Speedometer
Upper Right
 None
 Compass
 Outside Temp
 Time
 Range To Empty
 Average Econ (or L/100km, km/L)
 Current Econ (or L/100km, km/L)
 Trip A Distance
 Trip B Distance
Gear Display — If Equipped
 Full
 Single
Current Gear — If Equipped
 On
 Off
Odometer — If Equipped
 Show
 Hide
Favorite Menus
 Speedometer
 Vehicle Info
 Off Road – If Equipped (show/hide)
 Driver Assist – If Equipped (show/hide)
 Fuel Economy (show/hide)

 

[oldcjguy]

How do I know what gear I am in any one moment? Is there some screen in the display/dash that can tell me?

Along with the setup screen options others have described, you can also just slide the shifter over to manual mode. The dash cluster will change to show your current gear.

 

[roaniecowpony]

So I know there are several threads on regearing, but they mainly centered on what ratio to go with. I want to know the why’s. 2018 JLU Sport S, 3.6, auto, 35x12.5x17 MT Baja Boss AT, 2.5-3” lift(already installed when purchased used).

Why should I spend ~$3000 to regear just because I have 35s and a lift?
Is it just about seeing 8th gear again?
mpg improvement? How much?

Or is there a mechanical/performance reason?

I am not a mechanic nor pretend to be one, so please don’t get to technical.

If you are planning on any rock crawling, re-gearing isn't the best bang for your buck. A Rubicon transfer case can be had for half or less the cost of regearing and will give you 4:1 in 4 Low range. Your current transfer case is 2.7:1 ratio in 4 Low.

Regearing is more about highway cruise and street acceleration than off-road capability.

If you want both, probably the best route is Rubicon axles and the Rubicon transfer case.

 

[Stuckinthesand]

So I know there are several threads on regearing, but they mainly centered on what ratio to go with. I want to know the why’s. 2018 JLU Sport S, 3.6, auto, 35x12.5x17 MT Baja Boss AT, 2.5-3” lift(already installed when purchased used).

Why should I spend ~$3000 to regear just because I have 35s and a lift?
Is it just about seeing 8th gear again?
mpg improvement? How much?

Or is there a mechanical/performance reason?

I am not a mechanic nor pretend to be one, so please don’t get to technical.

19 JLUS with pretty much same setup with 68k miles on it. 45k miles since I put on 35"s and never did a regear. I wheel a few times a year on rocks. My commute for work is 17 miles highway each way 5 days a week. Kids sports have me traveling all over. I haven't regretted not going to a different gear set. I don't see 8th gear as often especially after 72mph. Maybe because I use a throttle controller I don't notice it. If I ever went to 37"s I would seriously consider a regear. 8th gear in these transmissions were really all about the CAFE requirements. You basically have 2 overdrive gears with 7th and 8th. I cruise down the highway at 80mph in 7th at around 2300rpm. The 3.6 loves the higher rpm range because that where it makes its power.

 

[ParadigmDawg]

I was surprised when I went from 33s to 37s. I assumed my shop would insist on regearing since I have 3.73s. They never mentioned it during my build and near the end of installation, I asked them. They said to just leave it and see what I think for awhile and that it may be just fine.

The day after it was completed, I had a 6 hour drive, wheeled for 5 days including 4 BOH trails and the 6 hours back home. It pretty much seemed perfect.

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