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Impressions from a 5.13 gears install on a JL Wrangler Unlimited Rubicon (JLUR)

crazy90'skid

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I haven't seen anyone mention this yet but the valve lift changes with the 3.6 at 2800 rpm from a more efficient range to more power. So before you choose a ratio make sure you are not in a cruising range near or above that rpm to have a hope for decent economy and ,more importantly imo, range. Most people probably know that cruising on the highway at 3k is a bad idea, but because of that camshaft changing valve loft at 2800 I'd expect to see a steep drop off in mpgs.
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I drove all day on I95 from Daytona Florida to Fayetteville North Carolina yesterday and set the cruise at 80 to 81 mph just to keep up with the flow of traffic. I averaged 14.9 mpg for the day. The rpms were at or about 2600.
 

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My comments are meant to provide perspective and not intended to counter other opinions on here.
It really comes down to what you are using your Jeep for, because I live in the foothills and my JL is not my primary vehicle, after time on the road and the trail, 5.13 is absolutely the right gearing for my needs. There are many that say the factory 4.10 gears are fine on 37 or 38 inch tires but they may need to drive one with 5.13's or drive one with factory size tires to remind them how nice it is to have the gearing closer to the engineered spec.. I was in deep snow last weekend and the only way to make progress was to drop tire pressure to 4 lbs and let her barely crawl over the top. This would not have been as affective with the 4.10's as the increased crawl speed would cause my tires to spin slightly and not float as well.. If you are mostly freeway and more of an overlander, 4.88 may be the best path, more technical wheeling and less highway, 5.13 again, with 37 or 38" tires. Reviewing the Grimmreaper web page and calculating your gearing with your model TC and transmission will provide you the information you need.
In the case of 37 or 38" tires, Rubicon 3.6 with 8 speed auto, 5.13 will put you a few hundred RPMs higher at 80 in 8th, 4.88 will place you very close to the RPM of factory gears with factory tires. Either is an improvement over 4.10 and gets the Jeep closer to factory torque cruise RPM and more efficient at getting the Jeep moving from a stop. The more weight that is added to the Jeep, the more leverage will help get it moving efficiently

JL Rubicon with 4 to 1 TC and 8 speed transmission:

Factory 4.10 with 32" Tire
Crawl at 750 RPM) Idle- 81 feet per minute
Highway 80 MPH-2307 RPM

4.10 with 37" tires-
Crawl at 750 RPM) Idle- 97 feet per minute
Highway 80 MPH- 1996 RPM

4.88 with 37" tires-
Crawl at 750 RPM) Idle- 79 feet per minute
Highway 80 MPH- 2375 RPM

5.13 with 37" tires-
Crawl at 750 RPM) Idle- 75 feet per minute
Highway 80 MPH- 2497 RPM

I personally prefer 70 on the freeway.
5.13 with 37" tires-
Highway 70 MPH- 2185 RPM

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

Knowing the improvements, I would have made the change sooner. Doing it myself made it very affordable but even paying a shop, it's still great bang for your buck.
 

Gadgettr1

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My comments are meant to provide perspective and not intended to counter other opinions on here.
It really comes down to what you are using your Jeep for, because I live in the foothills and my JL is not my primary vehicle, after time on the road and the trail, 5.13 is absolutely the right gearing for my needs. There are many that say the factory 4.10 gears are fine on 37 or 38 inch tires but they may need to drive one with 5.13's or drive one with factory size tires to remind them how nice it is to have the gearing closer to the engineered spec.. I was in deep snow last weekend and the only way to make progress was to drop tire pressure to 4 lbs and let her barely crawl over the top. This would not have been as affective with the 4.10's as the increased crawl speed would cause my tires to spin slightly and not float as well.. If you are mostly freeway and more of an overlander, 4.88 may be the best path, more technical wheeling and less highway, 5.13 again, with 37 or 38" tires. Reviewing the Grimmreaper web page and calculating your gearing with your model TC and transmission will provide you the information you need.
In the case of 37 or 38" tires, Rubicon 3.6 with 8 speed auto, 5.13 will put you a few hundred RPMs higher at 80 in 8th, 4.88 will place you very close to the RPM of factory gears with factory tires. Either is an improvement over 4.10 and gets the Jeep closer to factory torque cruise RPM and more efficient at getting the Jeep moving from a stop. The more weight that is added to the Jeep, the more leverage will help get it moving efficiently

JL Rubicon with 4 to 1 TC and 8 speed transmission:

Factory 4.10 with 32" Tire
Crawl at 750 RPM) Idle- 81 feet per minute
Highway 80 MPH-2307 RPM

4.10 with 37" tires-
Crawl at 750 RPM) Idle- 97 feet per minute
Highway 80 MPH- 1996 RPM

4.88 with 37" tires-
Crawl at 750 RPM) Idle- 79 feet per minute
Highway 80 MPH- 2375 RPM

5.13 with 37" tires-
Crawl at 750 RPM) Idle- 75 feet per minute
Highway 80 MPH- 2497 RPM

I personally prefer 70 on the freeway.
5.13 with 37" tires-
Highway 70 MPH- 2185 RPM

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

Knowing the improvements, I would have made the change sooner. Doing it myself made it very affordable but even paying a shop, it's still great bang for your buck.
Great post.... you make me want to swap gears. But, I wonder the implications for the factory warranty. I have the extended Mopar warranty on my 2020 JLUR. Currently I'm running 315 Ridge Grapplers but when those wear out I'm debating on going to 37's with perhaps a gear swap. 5.13s are very tempting.... curious as to how if affects mileage versus those running 37's with 4.88s (8 speed with the 3.6).
 

Call911man

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Great post.... you make me want to swap gears. But, I wonder the implications for the factory warranty. I have the extended Mopar warranty on my 2020 JLUR. Currently I'm running 315 Ridge Grapplers but when those wear out I'm debating on going to 37's with perhaps a gear swap. 5.13s are very tempting.... curious as to how if affects mileage versus those running 37's with 4.88s (8 speed with the 3.6).
I don't know about the warranty but imagine they would no longer cover the locker or gears but probably not a huge concern. As to mileage, I will offer only what I know as fact. I picked up about 2 MPG around town going from 4.10 to 5.13 on 38's. I don't drive the freeway much but there has been an improvement there as well. I would assume the 4.88's will offer slightly more on the freeway.

Be sure to calculate weight into your decision

The weight of cargo, passengers, larger and heavier tires, wheels, mods and lowered aerodynamics from raised height will have the greatest impact on mileage. Keep this in mind when choosing add ons.

For example, a rough way to calculate HP is ET through a 1/4 Mile for a given weight

Stock Jeep JLU 4500 lb vehicle taking 16 seconds to complete a 1/4 mile from a dead stop requires roughly 217 horsepower to do so. Add 500 lbs and it takes 241, make it 5500 and it takes 265 hp, an 11 and 22 percent increase in demand on the engine based on this coarse example as reality it is not linear.

Review the Torque curve for your vehicle to determine what torque is available at any given RPM. For me, knowing that I live in the hills and therefore often moving this weight from a stop and up and over hills, I want to take advantage of the increased torque at slightly higher RPMs.

Google tells us " Torque is a twisting force that speaks to the engine's rotational force and measures how much of that twisting force is available when an engine exerts itself"

HP and Torque curve- https://www.automobile-catalog.com/..._wrangler_4-door_sahara_3_6_v6_automatic.html

Rough numbers for the 3.6 L-
120 Ft lbs @ 1000 RPM
170 Ft lbs @ 1500 RPM
220 Ft lbs @ 2000 RPM

37" Tires on JLU:
Factory (32")-4.10 gears 25 MPH in 4th Gear = 1797 RPM 185ish torque
4.10 gears 25 MPH in 4th Gear = 1554 RPM 175ish torque
5.13 gears 25 MPH in 4th Gear = 1945 RPM 220ish torque

Factory (32")-4.10 gears 35 MPH in 5th Gear= 1929 RPM 210ish torque
4.10 gears 35 MPH in 5th Gear = 1668 RPM 180ish torque
5.13 gears 35 MPH in 5th Gear = 2087 RPM 215ish torque

So 5.13 puts me closer to my desire for increased torque for where I spend most of my time on the road.

If most of my time was spent on the highway and mileage was my top priority, i'd be looking at 7th and 8th gear. Paying attention to what gear your vehicle is in at given speeds with priority on highway, the gear and RPM and make changes accordingly.

Factory (32")-4.10 gears 70 MPH in 8th Gear = 2019 RPM 185ish torque
4.10 gears 70 MPH in 8th Gear = 1746 RPM 185ish torque
4.88 gears 70 MPH in 8th Gear = 2078 RPM 215ish torque
5.13 gears 70 MPH in 8th Gear = 2185 RPM 225ish torque
 

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I don't know about the warranty but imagine they would no longer cover the locker or gears but probably not a huge concern. As to mileage, I will offer only what I know as fact. I picked up about 2 MPG around town going from 4.10 to 5.13 on 38's. I don't drive the freeway much but there has been an improvement there as well. I would assume the 4.88's will offer slightly more on the freeway.

Be sure to calculate weight into your decision

The weight of cargo, passengers, larger and heavier tires, wheels, mods and lowered aerodynamics from raised height will have the greatest impact on mileage. Keep this in mind when choosing add ons.

For example, a rough way to calculate HP is ET through a 1/4 Mile for a given weight

Stock Jeep JLU 4500 lb vehicle taking 16 seconds to complete a 1/4 mile from a dead stop requires roughly 217 horsepower to do so. Add 500 lbs and it takes 241, make it 5500 and it takes 265 hp, an 11 and 22 percent increase in demand on the engine based on this coarse example as reality it is not linear.

Review the Torque curve for your vehicle to determine what torque is available at any given RPM. For me, knowing that I live in the hills and therefore often moving this weight from a stop and up and over hills, I want to take advantage of the increased torque at slightly higher RPMs.

Google tells us " Torque is a twisting force that speaks to the engine's rotational force and measures how much of that twisting force is available when an engine exerts itself"

HP and Torque curve- https://www.automobile-catalog.com/..._wrangler_4-door_sahara_3_6_v6_automatic.html

Rough numbers for the 3.6 L-
120 Ft lbs @ 1000 RPM
170 Ft lbs @ 1500 RPM
220 Ft lbs @ 2000 RPM

37" Tires on JLU:
Factory (32")-4.10 gears 25 MPH in 4th Gear = 1797 RPM 185ish torque
4.10 gears 25 MPH in 4th Gear = 1554 RPM 175ish torque
5.13 gears 25 MPH in 4th Gear = 1945 RPM 220ish torque

Factory (32")-4.10 gears 35 MPH in 5th Gear= 1929 RPM 210ish torque
4.10 gears 35 MPH in 5th Gear = 1668 RPM 180ish torque
5.13 gears 35 MPH in 5th Gear = 2087 RPM 215ish torque

So 5.13 puts me closer to my desire for increased torque for where I spend most of my time on the road.

If most of my time was spent on the highway and mileage was my top priority, i'd be looking at 7th and 8th gear. Paying attention to what gear your vehicle is in at given speeds with priority on highway, the gear and RPM and make changes accordingly.

Factory (32")-4.10 gears 70 MPH in 8th Gear = 2019 RPM 185ish torque
4.10 gears 70 MPH in 8th Gear = 1746 RPM 185ish torque
4.88 gears 70 MPH in 8th Gear = 2078 RPM 215ish torque
5.13 gears 70 MPH in 8th Gear = 2185 RPM 225ish torque
I don’t see 8th gear too often on the highway unless barely feathering the throttle or downhill. My JLUR is fairly heavy with full skid plates (aluminum underbody, but steel diff Covers, skids and LCA skids), winch, various Maximus-3 parts, Mopar lift etc etc. One of these days I’ll have to get it on a scale.

I can run 0-30 and 0-60 times on my Taser :)

Thanks again for an informative post!
 

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Reading all this has really helped, I’m between 4.88 and 5.13, I’m currently running 37x13.50x18 ridge grapplers. The only thing different is I have the 2.0t, so does anyone know or have any idea which would be best?
 

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Reading all this has really helped, I’m between 4.88 and 5.13, I’m currently running 37x13.50x18 ridge grapplers. The only thing different is I have the 2.0t, so does anyone know or have any idea which would be best?
Call Revolution Gear and ask them. Also call Yukon. See if they tell you the same. Bet they say 5.13.
 

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Reading all this has really helped, I’m between 4.88 and 5.13, I’m currently running 37x13.50x18 ridge grapplers. The only thing different is I have the 2.0t, so does anyone know or have any idea which would be best?
My two cents, 1.) I don't have first hand knowledge as I have the V6. However, after a trip through the rubicon, I love what the 5.13's did in the rocks with decreased crawl speeds allowing greater control. Either will be an improvement over stock. While the Turbo offers greater total torque, the V6 has the advantage right off idle, crawling is at idle and a lower gear would provide greater leverage right off idle where the 4i has yet to make much boost.
Both engines have the same 0-60 time in the Wrangler. The V6 starts off stronger but the i4 catches up at higher RPMs.
-Mud, Dirt roads and Daily driver might lean to higher gearing like the 4.88
-Rocks and slow tight trails would lean to lower gears like the 5.13
-5.13 won't affect your ability to cruise on the freeway at 70 or 80 with either engine
 

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My two cents, 1.) I don't have first hand knowledge as I have the V6. However, after a trip through the rubicon, I love what the 5.13's did in the rocks with decreased crawl speeds allowing greater control. Either will be an improvement over stock. While the Turbo offers greater total torque, the V6 has the advantage right off idle, crawling is at idle and a lower gear would provide greater leverage right off idle where the 4i has yet to make much boost.
Both engines have the same 0-60 time in the Wrangler. The V6 starts off stronger but the i4 catches up at higher RPMs.
-Mud, Dirt roads and Daily driver might lean to higher gearing like the 4.88
-Rocks and slow tight trails would lean to lower gears like the 5.13
-5.13 won't affect your ability to cruise on the freeway at 70 or 80 with either engine
Ok thanks!
 

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Reading all this has really helped, I’m between 4.88 and 5.13, I’m currently running 37x13.50x18 ridge grapplers. The only thing different is I have the 2.0t, so does anyone know or have any idea which would be best?
While I do not regret 37/12.5/17 STT Pros on 5.13s with the 3.6, having driven 37/12.5/17 KM3s on 4.10 with the 2.0 this weekend, I would do 4.88s since the turbo gives additional get up and go over the 3.6 and you won’t have to sacrifice some fuel economy on the highway and reduced pinion strength.
 

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https://bt39.com/GearWheelSpeed shows stock, 41.8" tires with 5.38 (my rig) and that's almost identical to stock. 37" & 4.88 almost identical too. You can edit any field you like and get the results. I can clean up the interface but it works OK for 30 minutes of work.
 

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“reduced pinion strength.”
Not true.
Call Revolution Gear and they’ll tell you the same pinion is used in both 4.88 and 5.13 gear sets.
 

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“reduced pinion strength.”
Not true.
Call Revolution Gear and they’ll tell you the same pinion is used in both 4.88 and 5.13 gear sets.
@chevymitchell do you have pics showing the two? I thought it was you who posted a pic long ago showing the smaller pinion.
 

chevymitchell

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“reduced pinion strength.”
Not true.
Call Revolution Gear and they’ll tell you the same pinion is used in both 4.88 and 5.13 gear sets.
The pinion's are absolutely different size. How do you think they change the ratio? The ring gear doesn't change it's diameter, it only gets thicker. A thicker ring means a smaller pinion gear must be used. I've never heard such a thing.

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