Do I need to regear?

[Fatboy97]

What the title said... Is it necessary to regear?

Fairly new to Jeep, I've had my Rubicon 3.6L V6 8-speed automatic for about 3 years now but I've kept it pretty much stock. I finally changed my stock Rubicon wheel/tire combo which weighted around 73lb to BFG LT315/70R17C tires that weights 64lb and G-FX TR12 wheels that weights 33lb each. I'm at least +24lb on each wheel.

Any critic is welcome, thanks!

Many people will say it’s not needed with your engine and transmission set up and I would almost agree. I have the Rubicon with 3.6 auto and the same tires you have and regearing to 4.56 made a huge difference. You will be very happy if you do regear.

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[grimmjeeper]

Thanks for the info, I wouldn't go to lockers or anything so just straight regear, most likely won't do it but we can dream! Wanna send the kids to private school, so basically paying for college before college...priorities!!!

Publik educashun werked fer me! ?

I hear ya. Just adding to the discussion so you have information to make a better decision that works for you.

 

[Renrens91]

Many people will say it’s not needed with your engine and transmission set up and I would almost agree. I have the Rubicon with 3.6 auto and the same tires you have and regearing to 4.56 made a huge difference. You will be very happy if you do regear.

Noted! How come you didn't go 4.88? I’ve just ordered the high top fender flare that the xtreme recon has to help with clearance and will probably install the 2.5’’ mopar lift kit down the line. I guess I'm trying to prep if ever I will upgrade to 37 when my current tire run its course.

 

[Vinman]

Here’s my experiences with tire/gear ratio combo while running the 3.6 with auto transmission.
- Stock 4.10’s with 35” KO2’s- fine for all driving conditions, best fuel economy.
- 5.13’s with the same tires, awesome go-kart like driving experience, took a hit on fuel economy.
- 5.13’s with 37” KO2’s, perfect combination of power and drivability, no problem staying in 8th gear at highway speeds and crawls awesome. Took another hit on fuel economy.

If I were to get another Jeep with the same engine/tranny combo and ran 35’s or 37’s, I’d choose 5.13’s again.

Should note that most of my driving is 3,500-6,000 ft elevation and highway speeds are usually limited to about 70-75 MPH

I know lots of people just accept a lower ratio numerically and just not run 8th gear but that makes no sense to me. Why have an 8 speed and not use all the gears?

 

[Fatboy97]

Noted! How come you didn't go 4.88? I’ve just ordered the high top fender flare that the xtreme recon has to help with clearance and will probably install the 2.5’’ mopar lift kit down the line. I guess I'm trying to prep if ever I will upgrade to 37 when my current tire run its course.

Mostly used on road with occasional trips to the beach. I also have a 2 door. I think maybe I would do 4.88 if I had the 4 door especially if you might be thinking about bigger tires in the future.

 

[grimmjeeper]

Noted! How come you didn't go 4.88? I’ve just ordered the high top fender flare that the xtreme recon has to help with clearance and will probably install the 2.5’’ mopar lift kit down the line. I guess I'm trying to prep if ever I will upgrade to 37 when my current tire run its course.

If you're considering 37s, I might want to keep the 4.10s now and go to 5.13s when you do the 37s. Save money today and toss it in a CD. Earn some interest while rates are up and have more for tires and gears down the road.

 

[2nd 392]

If you decide to re-gear consider isotropic finish. Worth the $125 per set just to eliminate the break in heat cycles without the other advantages. Will at East Coast Gear Supply sent them to Gear FX, them to me so it wasn’t even an extra hassle….. he said I always recommend Dana for these (D-44)

 

[Zandcwhite]

First off, weight of the tire is less than 10% of the reason to regear. It only matters when choosing to round up to the next higher numeric ratio. Tire diameter is 90% of the reason to regear. Don't worry about the weight. It just doesn't matter much.

Do you need to regear? Strictly speaking, no. You can get by with 4.10s. That is an adequate ratio to get the Jeep around on the streets with that size tire. It's not optimal but it works.

Do you want to regear? That depends. How do you use your Jeep? Daily driver? Off road? What kind of off road and how often? How often do you get up into high mountains?

All of that affects the regear decision.

Personally, I'd run 4.88s with the 3.6 engine. Even for a daily driver. But I probably run at higher elevation and I rock crawl with my Jeeps.

I will say that if you do regear, going to 4.56 isn't enough of a change to be worth the money. Go up to 4.88 if you do regear.

Final note. A lot of people say 4.10s are fine for those tires. But until you drive a Jeep with the right axle ratio to match the engine, transmission, and tire size you don't know what you're missing. Almost no one posts about how they regret regearing. They only regret they have is not doing it sooner.

That's why I post on most of these threads as I absolutely regretted regearing the 2019 JLUR. It was better on the freeway with 4.10s and 38s than it was with 5.38s. Sure I didn't see 8th gear much, although coming down a grade it was nice that it would drop below 2k rpms at 85mph. After the 5.38s it was in 8th gear by 40mph with nowhere to go but higher in rpms. With the 4-1 transfer case I never once felt like it needed more gear crawling in the biggest rocks including the Rubicon and telluride area trails at high elevations. With the 5.38s I found I rarely used 4lo any more as only the toughest obstacles needed it, not really any gain there. With the 2.0t it actually lost a half second 0-60 as it was shifting 1 extra time right before 60mph. Even with the 4.56 gears and stock 35s with the 3.6L on our 2022 I felt it was geared too low. For 37s I wouldn't go deeper than that. Even now on 39s it feels great on and off road. 4.88s would be a little better, but not worth the cost. Again, I drive faster than most on and off road. 90 isn't rare on the freeway or in the desert.

 

[Zandcwhite]

Here’s my experiences with tire/gear ratio combo while running the 3.6 with auto transmission.
- Stock 4.10’s with 35” KO2’s- fine for all driving conditions, best fuel economy.
- 5.13’s with the same tires, awesome go-kart like driving experience, took a hit on fuel economy.
- 5.13’s with 37” KO2’s, perfect combination of power and drivability, no problem staying in 8th gear at highway speeds and crawls awesome. Took another hit on fuel economy.

If I were to get another Jeep with the same engine/tranny combo and ran 35’s or 37’s, I’d choose 5.13’s again.

Should note that most of my driving is 3,500-6,000 ft elevation and highway speeds are usually limited to about 70-75 MPH

I know lots of people just accept a lower ratio numerically and just not run 8th gear but that makes no sense to me. Why have an 8 speed and not use all the gears?

Conversely why be in 8th gear at any speed over 40mph? 5.38s was too low for that reason with 38s. 35s with 5.13s would be worse. I'd bet under light acceleration it would be in 8th gear by 35mph. An 8 speed with 2 overdrive gears shouldn't be in the top gear before it gets to 50% of freeway speed in my opinion, defeats the purpose of 2 overdrive gears.

 

[Vinman]

Conversely why be in 8th gear at any speed over 40mph? 5.38s was too low for that reason with 38s. 35s with 5.13s would be worse. I'd bet under light acceleration it would be in 8th gear by 35mph. An 8 speed with 2 overdrive gears shouldn't be in the top gear before it gets to 50% of freeway speed in my opinion, defeats the purpose of 2 overdrive gears.

I would still rather have a super low 1st and a useable top gear than a higher 1st gear and unusable top gear. At least I can still use all 8 gears. I like that with my setup I rarely feel like I’m running out of power, and trust me, after many, many years of driving 4.0 powered TJ’s on 35” tires I absolutely welcome the combo I have now?

And think about what you said. If it shifts into top gear at 35 mph that is darn close to 50% of highway cruising speed for me.
But to each their own, I see where you’re coming from too. If you’re happy with whatever combination of tire size and gear ratio you have, thats all that matters.

 

[Zandcwhite]

I would still rather have a super low 1st and a useable top gear than a higher 1st gear and unusable top gear. At least I can still use all 8 gears. I like that with my setup I rarely feel like I’m running out of power, and trust me, after many, many years of driving 4.0 powered TJ’s on 35” tires I absolutely welcome the combo I have now?

And think about what you said. If it shifts into top gear at 35 mph that is darn close to 50% of highway cruising speed for me.
But to each their own, I see where you’re coming from too. If you’re happy with whatever combination of tire size and gear ratio you have, thats all that matters.

As a former tj and xj owner, I know full well how you feel about the 4.0L on the highway. Of course by comparison the JLUR with 4.10s has ridiculously low gears stock. The aw4 had a 2.8 first gear, in high range you'd need 6.88 axle gears in the tj/xj to match the 1st gear. Lo range you'd need 10-1 axle gears to match the crawl ratio of a stock Rubicon. Maybe it's the 2 decades of driving other Jeeps that have also skewed my opinion on gearing, but never once in a JL have I felt it needed more gearing in 1st Gear. I also love having a lifted jeep on big tires that will comfortably and even relatively efficiently roll 90+ if I want it to. In reality the super low 1st gear and super tall 8th gear make gearing a minimal issue at most as the jeep is still great compared to its predecessors no matter how you gear it.

 

[CarbonSteel]

Final note. A lot of people say 4.10s are fine for those tires. But until you drive a Jeep with the right axle ratio to match the engine, transmission, and tire size you don't know what you're missing. Almost no one posts about how they regret regearing. They only regret they have is not doing it sooner.

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

 

[Cutterone]

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

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...

 

[Renrens91]

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

Thank you for the detailed explanation.

 

[swanny2369]

No. Regearing is not a requirement until you are past 37's on a Rubicon. The 8 speed changed the game for the JL. 4.10's 3.5" on 37's 2.0T here in CO and the only time I have even thought about gearing was fully loaded climbing over Vail pass coming back from Moab in July. So DA would have been well north of 14000ft. Even then, I could still maintain 65 all the way uphill. I played the regearing game on both my last JKU's with 3.6's and 35's. 4.56 on the first and 4.88 the second. They simply are not required on JL's until your rig becomes very heavy.

The thing to keep in mind here is that rotational mass is a bigger killer to driveline power loss than overall tire diameter (within reason). 35's on heavy beadlocks most of the time will weigh more than most 37's on a simple aluminum wheel.

That said, whenever I make the jump to KMC's or some other type of beadlock. I will regear to 4.88's. But even those haven't proven to be a requirement yet.

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