4.56 Gearing...is it necessary? Ongoing research project.

Big500

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I have been thinking for awhile for those people who want bigger wheels and tires for the 392 and wanted to see if we can provide information for them so they can make an informed decision. As we all know the stock 392 comes with 3.73 gears and 33” tires. The Xtreme recon is fitted with 4.56 gears and 35” tires. I think that most would agree that if it was only based on loss of power from not re-gearing (I.e. Pentastar) the 392 has more than enough torque and HP to meet the requirements without re-gearing.

What I am interested in is whether it adversely affects the transmission, such as shifting points, or not being able to shift into 8th gear and stay in it as it normally would with the right gearing and tire size. In that vain I am going to post some pictures of my 392 extreme recon traveling at various speeds showing the following: Speed, RPMs, and the gear that the transmission selected. It would interesting to see if there are others who have 35’s or larger also post, pictures to see if the transmission is functioning normally or is not staying in the right gears.
For those who do not know this there is a way to switch your gear display from the PRND display to single gear which will show you which gear the transmission is in (I.e D1-D8). I have included pictures to show how it is done. I understand that there is a lot of variables like grade changes on the highway, but this is a start and not and ending.
 

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I have not driven a regular 392, but on my 2013 JK when I had 35's, going from 3.73 to 4.56 made a massive difference. Went from 5th gear being useless to being able to hold speed going up hills.
I think the 392 would be liveable with 3.73 and 35's but would certainly not be as able to hold speed and accelerate going up hills. Numerically higher (shorter) gearing improve acceleration by keeping engine in sweet spot of powerband. It does this by effectively giving you more gears at lower speeds because your higher gears in transmission are only useful at higher speeds. Tradeoff is that if you go too far then your engine is spinning too fast in higher gears. 4.56 with 35's results with engine rpm's being a higher than I would have initially liked.
I used to like the idea of a super deep overdrive and low rpm's when cruising to help improve fuel economy until I realized that only works on cars that are aerodynamic. GM used overdrive ratios of 0.5 on some corvette's back in the day to achieve mid 20's fuel economy on the highway although the vehicle would be a turd without downshifting.

I'm happy as a clam with 4.56 and 35's in the 392. I am getting about 14mg driving the jeep the way I like to drive it and it is a hoot. Ultimately gears are going to be a personal decision. I don't think you are hurting your transmission running 3.73s and bigger tires. I do think you are seriously hurting the fun factor losing over 20% power in every gear (the 20% power loss comes from the 20% drop in rpm and drop in torque because at the lower rpm engine torque is less because most driving is done below the torque peak).

You might get a little better fuel economy and some people might prefer that.

Oops, I just saw you have an extreme recon.........you have 4.56. You're fine. Transmission is happy with 4.56 and 35's. Plus don't think the 35's and 3.73's hurt the tranny either.

This guy has driven both and for him the 4.56 was a big upgrade.

Having said all that, there is only .5 second difference 0-60 between 392 and the XR. I think either is still awesome.

My daughter is critiquing my post. She said I should have written that it is a "beast" and not a "hoot"



 
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I own both and I answered all those questions, the 4.56 was done as the Bronco Bruiser. It came, it conquered, it left.

At 65-70 my Recon gets x fuel economy, when I get to 80 it gets better. Strange phenomena- NO

in order for the recon to be matched to the regular 392 it would need a 4.11 gear. it didnt get that because it would not have been able to put the smack down on the Bronco with a 4.11
 
I have seen this video before. As the extreme recon option is on hold for the foreseeable future anyone putting on larger wheels and tires will be putting them on themselves. Also the person speaking about the recon package only talked about the power feeling not the transmission complications that may result if you do not re-gear. This is what I am interested in long term.
 
I have owned two 2021 392’s.
The first one was stock 3.73 gears, my current 392 has 4.56 gears, 37” tires.
The 4.56 gears has noticeably MORE pep off the line.
The 3.73 gears with stock tires will have a little more top end speed than my current 4.56 gears with 37’s.
Fuel mileage between the two… the stock 392 with 3.73 gears gets a bit better fuel mileage vs the 4.56 with larger tires.
I average between 10-12.5 mpg, DEPENDING on how I feel like driving it with the 4.56 gears.
If I just cruise and “try”… I have achieved 14 mpg, but screw that!
I don’t drive it like I stole it, but I do take advantage of the 6.4 because that is WHY I bought it.
So… is it “necessary”?, no.
I do believe that going with larger tires such as 35’s, the 3.73 gearing is fine.
If you go with 37’s, the 4.56 gearing is much better as far as balanced torque WITH gobs of horsepower.
If going to larger tire size is what you wish to do, switching to a taller gear is a whole lot easier on your transmission vs “stressing” it by NOT doing so.👍🏼
 
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I posted this on another thread.
Hope it helps.

The gearing will be a preference more than anything. I have 35’s with the 3.73 and no complaints. My 2012 had 4.10 with 35’s and still manageable in Colorado throughout the western states. It also had the 5 spd auto. The 392 has more than enough power to turn 35’s with the 3.73 Along with tighter gearing on the 8 spd tranny.
personally, I didn’t like everything with the recon package, except the gearing and speed governed at 110mph. The gearing I can change easily enough if I ever want to go that route.
after the tires, Tazer, calibration, I’m solid where I am with my set up.
also, some prefer 3.73 for some fuel savings. Others want 4.56 for better torque. In the end, it‘s preference.

Now, if I were to go to 37’s, I would swap to 4.10 at minimum. While I’m in there, I would most likely go to 4.56 just to retain the torque, as that’s the WHOLE reason I bought a 392.
I’m even researching super chargers now. Horsepower is my addiction. Women and horsepower. Both expensive and will make you cry or laugh at some point.

somewhat unrelated, One other aspect I liked with the Recon, was the speed limiter at 110mph. However, I also had a GC SRT and regularly cruised at 90-100. Pushing past 85 in the 392 Rubi, is plenty enough. At 100, it’s a bit intimidating, and honestly, in my humble opinion, if I wanted speed, I would have kept my SRT.

back to gearing...
the simple questions only you have the answer to.
you want to save gas? Lower RPMs.
or, do you want more torque? Higher RPMs.
 
I have seen this video before. As the extreme recon option is on hold for the foreseeable future anyone putting on larger wheels and tires will be putting them on themselves. Also the person speaking about the recon package only talked about the power feeling not the transmission complications that may result if you do not re-gear. This is what I am interested in long term.
If you are running a 35 the 3.73 is fine, 37 or taller and you want a taller gear. Yes it will put more stress on the tranny but the drivetrain is warrantied for 100k I believe so most dont care.

Pedal Commander will mask the problem but its like a meat head doin roids, not good but won't see the long term damage until later and people live in the now.
 
While I agree the transmission is warranted a case could be made by a dealer that your switching to larger tires resulted in causing the transmission problems. It comes down to the dealer being cool. Here is a forum post that highlights what I was trying to go after when I created this post. I wasn’t interested in power or MPG changes as those have been discussed to death.

Now I understand that the post talks about 37’s rather than 35’s, but it is about the loss of 7 and 8 gear that I am trying to highlight.

 
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I put 37x13.5x20 on my 392 the first day I took delivery before the Recon was an option. It would go into 8th gear even at 85 mph but only for a short time. It down shifted on every overpass, headwind etc. I was then able to drive a stock one. I felt like the mid power band is where mine was lacking compared to the stock one. So I regeared to 4:56….Better off the line and the mid power band is better for sure. It NEVER searches for 8th gear anymore. 80 mph going over an overpass against the wind and it still doesn’t down shift. At 80 I’m 3-400 RPMs higher than stock. My gas mileage is about the same. Worse some days, better others. I tend to drive it like a race car tho. Just my 2 cents. Remember I have a very heavy wheel set up with 37x13.5x20
 
I've had the standard 392 for about 5 months now. I had the dealer change the 33's for 35's before I even drove it. I did the Livernois tune in the first month of owning it. The 3.73 gears were good, and there was always plenty of power. I recently swapped to 4.56 gears and there is a very big difference off the line. It seems to have added about 200-300rpm for the same speed, but for me the 4.56 was worth it.

And yes, I would have purchased the XR if I had ordered. My dealer had someone cancel back in August, so I said I would take it. I had it 2 weeks later and paid under invoice for it. Sometimes you take what you can get. :)
 
I have 35s on my 392. I live at altitude and the transmission has no problem staying in 8th. 3.73 is perfect for 35s on a 392. I had 4.10 on the 3.6 with with 34s, it was an absolute dog here at altitude, I never went to 35s because it wasn’t livable with the 34s. 4.56 is good for 37s or 39s. Totally not needed for a 35s 392, on and off road.
 
This forum (and thread, in particular) rocks!! That is all.

Edit - Okay...that is not all.

After reading the thread, and determining I need to swap out the gears (I'm running 37's), my only noob question for you guys is: who/where should I purchase my gears from? Should I go for the complete kits that are available or just the rings and pinions? Extreme Terrain offers multiple options, for example.

Thoughts?

Tim
 
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The way my mind works if the XR has 4.56 with 35’s, if I go 37’s I should run 4.88s.

Might be too much, but we’ll see. So far it’s just a battle between the “4.56 is great” crowd and the “why regear? It runs fine” crowd. The debate is maddening (and, ultimately no help when you realize it’s just all opinion wars with no hard data, just anecdotal evidence.

So much tribal knowledge out there from people who have been there and done that, but I really don’t know who to believe so I’m just doing my thing…..4.88’s and 37s. If I don’t like them, honestly I may just dial up the coil overs to 5” lift, get some flat fenders, and go to 40s.

Literally no difference in stability with the 37s vs the 33s.
 
This forum (and thread, in particular) rocks!! That is all.

Edit - Okay...that is not all.

After reading the thread, and determining I need to swap out the gears (I'm running 37's), my only noob question for you guys is: who/where should I purchase my gears from? Should I go for the complete kits that are available or just the rings and pinions? Extreme Terrain offers multiple options, for example.

Thoughts?

Tim
Couple things. Wait to regear a little bit to find out if you stay with 37s or maybe you are thinking about bigger. That way you only do it once. If you go bigger then skip the regear and upgrade the whole axles.

@deanfromoregon simple answer is that it is personal preference. Some straight truth here is that 4.56 will give you harder acceleration. But is not be needed for normal driving. You get a .3 to .5 second off 0-60 At the expense of MPGs. People have regeared Jeeps forever because of small engines and bigger tires. This is not that. My 392 with 3.73 and 35s is as fast or faster off the line than many pure play sports cars. I don’t drag stop light to stop light. It is plenty fast. I bought it as a Jeep to get to places that are difficult to get to… it is still that, just has a lot of power when needed.
 
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This forum (and thread, in particular) rocks!! That is all.

Edit - Okay...that is not all.

After reading the thread, and determining I need to swap out the gears (I'm running 37's), my only noob question for you guys is: who/where should I purchase my gears from? Should I go for the complete kits that are available or just the rings and pinions? Extreme Terrain offers multiple options, for example.

Thoughts?

Tim
If (or when 😉) I upgrade I am leaning towards the Dynatrac Hard Core PLUS XD60/XD60 Axle Set with Eaton ELocker4 with 4.56 ring and pinion.
I like that it gets rid of the stupid FAD (forward disconnect) that is not installed and just a cast fork cover :rolleyes: in the 392 4H Auto system. It also retains the electronic locker system which keeps it more stock OEM.

I really like @Big500 idea of posting some real world pics. I will do so when my 392 gets back from PPF. The general rule of thumb is that you gear for highway speeds not the drag stip. For the 3.6 Pentastar that has been: 3.73 = 31”; 4.10 = 33” ; 4.56 = 35” ; 4.88 = 37” but that probably doesn’t translate well to the 392; you can run 37’s at 3.73, it obviously has been done and that big V8 doesn't play by the regular rules. It would be cool to see one of these tire size to gear ratio charts specifically for the 392.
Screen Shot 2022-03-09 at 4.17.59 PM.png

In the end the acceleration of the XR with 35” at 4:56 is just basic engineering not some kind of magic Xtreme pixie dust. A 4.10 ratio would probably been more logical choice but Jeep wanted a Sasquatch Stomper so they turned the Amp up to 11. There is a cost to that, in engineering there are always trade offs.
 
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I think we are more looking at gearing from the muscle car era with the 392. Back in the day cars had 2.77 for highway cars or 3.55 or higher for drag cars. Totally driver choice. Similar with the 392.

With all other Jeeps you tried to balance ratio with tire size so the Jeep could still be road drivable. That is not the worry here. A 3.73 Jeep is still faster on 37s than any other jeep with any gearing ever made…. So decide what you are doing with your Jeep and figure from there.
 
This forum (and thread, in particular) rocks!! That is all.

Edit - Okay...that is not all.

After reading the thread, and determining I need to swap out the gears (I'm running 37's), my only noob question for you guys is: who/where should I purchase my gears from? Should I go for the complete kits that are available or just the rings and pinions? Extreme Terrain offers multiple options, for example.

Thoughts?

Tim
I had Yukon 4.88 on my 2015 JKU and will more than likely stick with Yukon if I decide to re-gear my 392.
 
This forum (and thread, in particular) rocks!! That is all.

Edit - Okay...that is not all.

After reading the thread, and determining I need to swap out the gears (I'm running 37's), my only noob question for you guys is: who/where should I purchase my gears from? Should I go for the complete kits that are available or just the rings and pinions? Extreme Terrain offers multiple options, for example.

Thoughts?

Tim
I went with Dana Spicer…lil pricey but so is this Jeep
 
The way my mind works if the XR has 4.56 with 35’s, if I go 37’s I should run 4.88s.

Might be too much, but we’ll see. So far it’s just a battle between the “4.56 is great” crowd and the “why regear? It runs fine” crowd. The debate is maddening (and, ultimately no help when you realize it’s just all opinion wars with no hard data, just anecdotal evidence.

So much tribal knowledge out there from people who have been there and done that, but I really don’t know who to believe so I’m just doing my thing…..4.88’s and 37s. If I don’t like them, honestly I may just dial up the coil overs to 5” lift, get some flat fenders, and go to 40s.

Literally no difference in stability with the 37s vs the 33s.
You would be fine with 4.56 or 4.88 with 37's. If even thinking of 40's, I'd go with 4.88's.

The reason the debate is all anecdotal, is that there is not much difference in fuel economy or wear and tear with a gear change. It is mostly a seat of the pants feel thing, but it is a big deal in the way it feels and different people are going to like different gears. I liked the 2.73 rear end in my twin turbo 91 mustang 5.0 when most everyone else was running 3.73 or 4.10. That thing had so much torque that I could spin the tires going 70mph in 2nd gear. Plus still get 20mpg + in 5th gear cruising. Just depends on what you like and that may change over time.

I think your thinking is spot on, but my thinking could be suspect ;)
 
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