Do I need to regear?

[ChoSunJuan]

To add onto @grimmjeeper's thoughts:

The 3.6L engine does not like to be lugged. If your Jeep is heavy, you tow, or you are at altitude, then 4.10s are going to be too high of a gear ratio with 35's and it sure as hell will not work with 37's.

I have lived through 2 regears with 3 sets of tire sizes, so while some may disagree, I know what I am talking about. I have done:

33's + 4.10s <--this was adequate, but not optimal; especially at altitude
35's + 4.10s <-- this positively sucked at sea level and altitude
35s' + 4.88 <-- this combination at sea level was the best all around driving experience
37's + 4.88 <-- this was livable at sea level, but sucked at altitude
37's + 5.13 <-- this combination at sea level was great, but only adequate at altitude

The 3.6L loses 3% of HP and TQ per 1000' elevation gain and it cannot afford to lose anything with its anemic 285HP/260TQ. Stellantis needs to grow a brain and install a powerplant that is 330HP/420TQ at a minimum.

Here is what I would do (and have) for a 3.6L/ZF8 transmission:

33's = 4.56
35's = 4.88
37's = 5.13
38+ = 5.38

Totally agree with you, Stellantis needs to put the standard output Hurricane engine in the Wrangler.

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[Xcoaste]

Personally, I like my Jeeps to drive as close to stock as possible. I would regear and I have whenever I changed my stock tire size. I don’t think you can get 35’s with 4.10 gears from the factory? So the engineer's must have their reasons for offering 4.56 /4.88. Whether that is worth $2k is up to you.

 

[grimmjeeper]

Personally, I like my Jeeps to drive as close to stock as possible. I would regear and I have whenever I changed my stock tire size. I don’t think you can get 35’s with 4.10 gears from the factory? So the engineer's must have their reasons for offering 4.56 /4.88. Whether that is worth $2k is up to you.

Engineers have a lot of reasons that have nothing to do with sound engineering principles. There are often economic or political (governmet, corporate, etc.) reasons for doing things that make no sense.

They do things like putting 3.45 gears in the axle with the 3.6 V6.

 

[Flip]

So you would recommend going to 4.88 with my 6sp even if I am only going up to a 33 (275-70-18)? Again I was thinking 4.56 would be plenty...

(quote) Here is what I would do (and have) for a 3.6L/ZF8 transmission:

33's = 4.56 ?
35's = 4.88
37's = 5.13
38+ = 5.38

 

[Xcoaste]

Engineers have a lot of reasons that have nothing to do with sound engineering principles. There are often economic or political (governmet, corporate, etc.) reasons for doing things that make no sense.

They do things like putting 3.45 gears in the axle with the 3.6 V6.

Yeah, but not with 35’s.

 

[Zandcwhite]

Yeah, but not with 35’s.

You don't need to be an engineer to understand basic math. 3.45 gears with 32" stock tires is equivalent to 4.10s with 38s. You can't get a stock Jeep with 37s so I guess we can't possibly run them? Obviously a lifted jeep on 37s isn't going to drive exactly like a stock sport, but it will shift at the same points, have roughly the same rpms at a given speed, etc. I think the stock Rubicon is a decent balance of deeper gearing for crawling and freeway rpm, especially once you up the tire size to 35". The XR felt geared too low on the freeway with 4.56s an 35s. In my opinion they engineered that package for 37s. They fit with no lift, the freeway rpms are better, the tire even fits on the tire carrier. For my use, including a lot of freeway roadtrips at 85mph and a lot of crawling I wouldn't go deeper than 4.56s for 37s. With the 39s we still see 8th gear regularly. For 39s I think 4.88s would be a better match, but not enough to drop $3k which is what gears cost locally. 4.56s would actually match a sports gearing with 42s which one could argue there is enough margin running 39s that our Jeep drives "more like stock" than most in the gearing department.

 

[ahmadtaha1988]

To add onto @grimmjeeper's thoughts:

The 3.6L engine does not like to be lugged. If your Jeep is heavy, you tow, or you are at altitude, then 4.10s are going to be too high of a gear ratio with 35's and it sure as hell will not work with 37's.

I have lived through 2 regears with 3 sets of tire sizes, so while some may disagree, I know what I am talking about. I have done:

33's + 4.10s <--this was adequate, but not optimal; especially at altitude
35's + 4.10s <-- this positively sucked at sea level and altitude
35s' + 4.88 <-- this combination at sea level was the best all around driving experience
37's + 4.88 <-- this was livable at sea level, but sucked at altitude
37's + 5.13 <-- this combination at sea level was great, but only adequate at altitude

The 3.6L loses 3% of HP and TQ per 1000' elevation gain and it cannot afford to lose anything with its anemic 285HP/260TQ. Stellantis needs to grow a brain and install a powerplant that is 330HP/420TQ at a minimum.

Here is what I would do (and have) for a 3.6L/ZF8 transmission:

33's = 4.56
35's = 4.88
37's = 5.13
38+ = 5.38

I am considering 4.56 for my 33 and shop is telling me I will have shifting issues... Is it BS or they know what they are talking about?

 

[Mudduck]

I am considering 4.56 for my 33 and shop is telling me I will have shifting issues... Is it BS or they know what they are talking about?

You can set your gear ratio and tire size with a tazer/j-scan etc… so you wont have shifting issues.
IMHO 4.56 and 33” will be too low. I run 35” (34.8”) Ultra terrains and 4.56, and it feels almost too low on the highway. Im in 8th gear at 47mph. 4.56 and 33, your RPMs will be higher, but it’ll scoot!

 

[CarbonSteel]

I am considering 4.56 for my 33 and shop is telling me I will have shifting issues... Is it BS or they know what they are talking about?

1000% BS...find another shop!

 

[Zandcwhite]

I am considering 4.56 for my 33 and shop is telling me I will have shifting issues... Is it BS or they know what they are talking about?

You won't have shifting issues, but you'll be in 8th gear by 40mph and spinning 2700rpms at freeway speed even under no load going down hill. Maybe that's what they mean by shifting issues. I felt 4.56 was a little too low for 35s at freeway speed. Now if you are planning 35s but doing the regear 1st I could see going to 4.56, but if you never plan bigger than 33s I'd go 4.10s.

 

[Vinman]

I have 5.13’s and with 37” KO2’s my Jeep spins exactly 2,000 RPM at 60 MPH, ideal in my opinion.

 

[Zandcwhite]

I have 5.13’s and with 37” KO2’s my Jeep spins exactly 2,000 RPM at 60 MPH, ideal in my opinion.

Perfect if you don't ever drive much over 60mph. Still 2650 rpms at 85mph which is a bit high for me.

 

[Vinman]

Perfect if you don't ever drive much over 60mph. Still 2650 rpms at 85mph which is a bit high for me.

These engines will run all day at 2,650 RPM and not complain one bit

 

[Zandcwhite]

These engines will run all day at 2,650 RPM and not complain one bit

They'll run all day at 4k too, both of which are options with a simple downshift and the point of an 8spd in my opinion. The point of 2 overdrives is not to drive around at moderate loads in 8th gear though. Low load, low rpm, 8th gear, maximum efficiency. Increase in Ioad, auto downshifts up to 7 times as needed to get the necessary gearing/rpm to meet the load. I think the stock Rubicon gearing is the sweet spot at about 2350rpm at 85mph. The sahara we rented in Hawaii felt like it could use a bit more gearing with the 3.45s and 32s. Our xr felt overgeared with the 4.56s and 35s in my opinion. Granted the massive selection of gearing in the 8spd minimizes the downsides of under or overgearing. Add in the crawl ratio with the 4-1 tcase and you can pretty much run any gearing you chose until you get into the extremes on either end. That being said, as someone who tends to drive faster than most, I'd pick 4.56s for 37s and save 5.13s for 40s but they are definitely liveable on 37s especially if you don't tend to drive 80+mph.

 

[MA Joop]

Definitely one of those things where opinions vary. I have the XR package with 315/70-17 and the 4.88 gearing option. Personally, I love it. I also have no issue blasting down the highway at 85 mph, the rpm is a touch high but the 3.6 doesn't seem to mind, though I will say fuel economy sucks.

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