Regearing 4:56 vs 4:88

[Ratbikerod]

I have a 2015 Rubicon JKU that I am currently running 33" tires on and have 3:73 gears. I will, at some point, probably move up to 35" tires. This is my daily driver and I tend to drive longer distances to do any off-roading, which is generally pretty mild.

Thus, I want to maintain some semblance of ok milage (typically get about 15 mpg today), but improve both driving and off-roading performance. Should I go with 4:56 or 4:88 gears. Won't be going to 35" until the 33" wear out.

Thoughts?

 

[pc1p]

You're in Texas flatlands and have a 0.83 OD ratio. Seeing how the 3.6L is powerful enough to manage moderate hills and headwind, many are happy with 4.56's with 35"s. However, if it were me I'd go with the 4.88's (actually I'd probably go 5.13's b/c ~2860 RPM at 70 MPH is quite smooth still and I'm in the "Endless Mountain" region of the northeast).

 

[Ratbikerod]

You're in Texas flatlands and have a 0.83 OD ratio. Seeing how the 3.6L is powerful enough to manage moderate hills and headwind, many are happy with 4.56's with 35"s. However, if it were me I'd go with the 4.88's (actually I'd probably go 5.13's b/c ~2860 RPM at 70 MPH is quite smooth still and I'm in the "Endless Mountain" region of the northeast).

View attachment 130732

Yea, I am mainly in Texas, so pretty much not a lot of big hill country. I do travel to New Mexico to vacation and it would come in more there. Sorry to be dumb, but OD to me is overdrive and the 5 speed has no OD I am aware of - school me if it does. The gear shop is pushing 4:88 and I am sure they know best. Just do not want to go too far on this as I do have to drive it on the highway frequently.

 

[tJKrider]

Sorry to be dumb, but OD to me is overdrive and the 5 speed has no OD I am aware of - school me if it does

Here are the gear ratios for the 5spd auto. As you can see 5th is indeed an overdrive as @pc1p stated:

1st (3.59), 2nd (2.19), 3rd (1.41), 4th (1.00), and 5th (0.83)

 

[Ratbikerod]

Here are the gear ratios for the 5spd auto. As you can see 5th is indeed an overdrive as @pc1p stated:

1st (3.59), 2nd (2.19), 3rd (1.41), 4th (1.00), and 5th (0.83)

Ok, yea thanks, we are on the same page. I did not look at 5th gear as OD. All good, thank you. So on your chart either 4:56 or 4:88's would work for either tire size in the blue performance band, but I slip into green on the 35's with 4:56. That would be in line with what I am being told, then.

 

[pc1p]

Yea, I am mainly in Texas, so pretty much not a lot of big hill country. I do travel to New Mexico to vacation and it would come in more there. Sorry to be dumb, but OD to me is overdrive and the 5 speed has no OD I am aware of - school me if it does. The gear shop is pushing 4:88 and I am sure they know best. Just do not want to go too far on this as I do have to drive it on the highway frequently.

Ok, yea thanks, we are on the same page. I did not look at 5th gear as OD. All good, thank you. So on your chart either 4:56 or 4:88's would work for either tire size in the blue performance band, but I slip into green on the 35's with 4:56. That would be in line with what I am being told, then.

You are correct - OD is indeed "overdrive". The W5A580 in your JK, commonly referred to as the "NAG1" is a Mercedes developed 5-speed Auto that replaced the older (and arguably WORSE transmission ever installed in a Jeep), the (in)famous 42RLE.

4.88's would keep you in the "blue". I always err on the "blue side" of gearing, as the Wrangler is essentially an aerodynamic "box" driving down the road and the engines all benefit from some additional torque multiplication.

FWIW, I'm running 5.13's in my daughter's 2010 Islander on 32"s, but her 42RLE is only a 4-speed auto and has a 0.79 OD ratio, plus the 3.8L falls a bit short of the 3.6L in power.

 

[Ratbikerod]

You are correct - OD is indeed "overdrive". The W5A580 in your JK, commonly referred to as the "NAG1" is a Mercedes developed 5-speed Auto that replaced the older (and arguably WORSE transmission ever installed in a Jeep), the (in)famous 42RLE.

4.88's would keep you in the "blue". I always err on the "blue side" of gearing, as the Wrangler is essentially an aerodynamic "box" driving down the road and the engines all benefit from some additional torque multiplication.

FWIW, I'm running 5.13's in my daughter's 2010 Islander on 32"s, but her 42RLE is only a 4-speed auto and has a 0.79 OD ratio, plus the 3.8L falls a bit short of the 3.6L in power.

Great info, thank you. Definitely will go with the 4:88's I think. Interestingly, I have a 2015 Ram 2 door short bed pickup with the same 3.6 motor but the 8 speed. Man does that 8 speed really wake the 3.6 up. I am hoping this gear change will as well.

 

[tJKrider]

The gear shop is pushing 4:88

actually I'd probably go 5.13's

Let me throw another fact out here for discussion. The JL Wranglers with an 8 spd auto and factory 35s (315/70R17) have a 4.56 final drive. OEM gears are typically a best fit to balance all use cases, fuel economy, etc. A big difference, however, is that the 8spd has a 4.71 first gear. To match that in a JK auto you would need a 5.98 final drive! (4.71/3.59) * 4.56 = 5.98

If you compare 2nd in the JL to first in the JK it looks a bit better:
(3.13/3.59) * 4.56 = 3.98

Something in between the two would be a good compromise, which would be 4.98. Closest actual gear choices would be the 4.88 or 5.13 depending on how you would want to hedge your own usage.

 

[pc1p]

Great info, thank you. Definitely will go with the 4:88's I think. Interestingly, I have a 2015 Ram 2 door short bed pickup with the same 3.6 motor but the 8 speed. Man does that 8 speed really wake the 3.6 up. I am hoping this gear change will as well.

The first time I drove a WK2 with a ZF 8-speed, I would have swore it had a V8. It really adds a whole new level of performance. When it came time to do my Hemi swap in my JKU, there was no question whether or not I was going with the 8HP70!

Let me throw another fact out here for discussion. The JL Wranglers with an 8 spd auto and factory 35s (315/70R17) have a 4.56 final drive. OEM gears are typically a best fit to balance all use cases, fuel economy, etc. A big difference, however, is that the 8spd has a 4.71 first gear. To match that in a JK auto you would need a 5.98 final drive! (4.71/3.59) * 4.56 = 5.98

If you compare 2nd in the JL to first in the JK it looks a bit better:
(3.13/3.59) * 4.56 = 3.98

Something in between the two would be a good compromise, which would be 4.98. Closest actual gear choices would be the 4.88 or 5.13 depending on how you would want to hedge your own usage.

When in doubt, go deeper….

I’ve never met someone who said “wow, I hate this gearing, it just provides too much torque multiplication and throttle control!”, but I’ve met dozens of people that have said “I should have gone 4.88/5.13/5.38/ whatever ratio is the next deeper than the one they got”.

Also probably worth noting that most of the Extreme Recon packaged JLUR’s in my area were optioned with 4.88’s - AND - the JLUR shed ~200 lbs compared to the JKUR. Given all that and the better transmission, I for sure would be going 5.13’s (but I’d also be dropping in a Hemi so, lol)

 

[Cimmerian]

I have a 2015 Rubicon JKU that I am currently running 33" tires on and have 3:73 gears.

I thought Rubis came stock with 4.10s. Did that change with the refresh?

 

[Ratbikerod]

I thought Rubis came stock with 4.10s. Did that change with the refresh?

From all my research, the automatics (which I have) came with 3:73’s and the manuals came with 4:11’s unless ordered differently.

 

[Ratbikerod]

The first time I drove a WK2 with a ZF 8-speed, I would have swore it had a V8. It really adds a whole new level of performance. When it came time to do my Hemi swap in my JKU, there was no question whether or not I was going with the 8HP70!



When in doubt, go deeper….
View attachment 130734


I’ve never met someone who said “wow, I hate this gearing, it just provides too much torque multiplication and throttle control!”, but I’ve met dozens of people that have said “I should have gone 4.88/5.13/5.38/ whatever ratio is the next deeper than the one they got”.

Also probably worth noting that most of the Extreme Recon packaged JLUR’s in my area were optioned with 4.88’s - AND - the JLUR shed ~200 lbs compared to the JKUR. Given all that and the better transmission, I for sure would be going 5.13’s (but I’d also be dropping in a Hemi so, lol)

I have really contemplated an 8 speed change. I just expect that it would be so god awful expensive. In my little 2 door short bed Ram it will completely light up the tires and scratch them hitting second. When I bought the Ram I wanted a Hemi, 2 door short bed in any color other than black. They had one remaining 2 door, it was black with the 3.6. I was impressed enough to buy it. I have 120k miles on it and it still runs like a bat outta hell. Working on it is easy as you can stand between the motor and the radiator. LOL