JLUR on 37s regear 4.56 or 4.88

Hailchaser

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I am wanting to regear. Some recommend 4.56 others say 4.88. Mostly highway driving with a once a month weekend wheelin trip. Would appreciate some feedback. Spoke to Northridge 4x4 and they recommend Dana/Spicer gears.





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Jkohler

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I'd have to vote for the 4.88 my self. I believe My math put me right around 2000 at 70 in 8th. I'd also say go with Dana/spicer gears
 

vavaroutsos

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Definitely use a Dana/Spicer gear set (not sure any others are even available for the Advantek yet anyhow). I would also vote for 4.88. I find 6th gear a little tall on the manual (8th on the auto must really be tall). A 4.88 ratio with 37" tires will be a bit shorter gearing than from the factory.

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DesertsJL

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I’m in the middle of a gear swap. 35” tires and 5.38 gears. I’ll post up when I’m done. The 8th gear is so tall you can get away with a higher gear.

Stock @ 70mph in 8th....1975rpm
Stock @ 70mph in 7th....2476rpm
35’s at 70 w/5.38 gears.....2422rpm

The motor will be turning less with the 5.38 and 35” tires than if you ran stock in 7th gear. For all those that have lost their 8th gear due to larger tires, don’t go to shallow on your gear selection.

Since upgrading to 35” tires the only time that I see 8th gear is on a downslope with a tail wind. May as well have a vehicle that is able to use all 8 gears rather than effectively reduce the capabilities of the vehicle to 7 gears.
 
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5280Sapper

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this is crazy.. I'm on 38's with 4.10's still and my jeep will cruise highway in Denver in 8th gear no problem... no clue what my rpms are I guess I'll check tomorrow at 70 for reference to yours @DesertsJL And I have mine reprogrammed with a Tazer. I was planning on just 4.88's for mine.
 
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Hailchaser

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this is crazy.. I'm on 38's with 4.10's still and my jeep will cruise highway in Denver in 8th gear no problem... no clue what my rpms are I guess I'll check tomorrow at 70 for reference to yours @DesertsJL And I have mine reprogrammed with a Tazer. I was planning on just 4.88's for mine.
Did you reprogram with the tazer at the same time when you installed the 38’s. Maybe I should try the tazer before regearing but my rpms we’re running supper high when driving through the Colorado mountains on I-70.
 

5280Sapper

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I did nothing for like 2 days till I finally drove up to Northridge to get a tazer! shockingly it wasn't horrible but the trans wasn't happy for sure. to much going on for it to shift correctly like it should. I still believe it could be better, I can't wait for HPTuners to release the license so I can get in there and FUQ with chit!!!!
 
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Hailchaser

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I did nothing for like 2 days till I finally drove up to Northridge to get a tazer! shockingly it wasn't horrible but the trans wasn't happy for sure. to much going on for it to shift correctly like it should. I still believe it could be better, I can't wait for HPTuners to release the license so I can get in there and FUQ with chit!!!!
Thanks. Let me know how your RPM’s look when you get a chance. I’m out of town but will hit with the Tazer when I get back. It’s sitting on the seat. Still think I want to regear just need to decide between 4.56 vs 4.88.
 

5280Sapper

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I'm right there with you.. its gunna happen just don't know where likely 4.88's but everyone is screaming 5 somethings and they aren't at altitude. And I wanna do a blower soon also! message me and we can link up you can drive mine if you want.
 

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http://www.grimmjeeper.com/gears.html
You can use this calculator and it will tell you everything. It took me a couple of times to figure it out but, it was very help full. I’m in southern Oregon running 37’s and the 4.10 don’t due bad. It’s just not that great either. I’m going to go 4.88 or 5.13’s.
 

offcamber

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I’m in the middle of a gear swap. 35” tires and 5.38 gears. I’ll post up when I’m done. The 8th gear is so tall you can get away with a higher gear.

Stock @ 70mph in 8th....1975rpm
Stock @ 70mph in 7th....2476rpm
35’s at 70 w/5.38 gears.....2422rpm

The motor will be turning less with the 5.38 and 35” tires than if you ran stock in 7th gear. For all those that have lost their 8th gear due to larger tires, don’t go to shallow on your gear selection.

Since upgrading to 35” tires the only time that I see 8th gear is on a downslope with a tail wind. May as well have a vehicle that is able to use all 8 gears rather than effectively reduce the capabilities of the vehicle to 7 gears.

I sure hope you are going way bigger than 35's because you are way overgeared with 5.38's and 35's. Do you have a manual? With the 8 speed auto there is zero reason to regear even on 37's. I can light my 37x13.5's up at will and it does 0-60 in about 7.7 seconds. I'm still getting 17-19mpg on the highway. I'm starting to think that the 8 speed auto is well worth the money...
 

DesertsJL

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I sure hope you are going way bigger than 35's because you are way overgeared with 5.38's and 35's. Do you have a manual? With the 8 speed auto there is zero reason to regear even on 37's. I can light my 37x13.5's up at will and it does 0-60 in about 7.7 seconds. I'm still getting 17-19mpg on the highway. I'm starting to think that the 8 speed auto is well worth the money...
The 8-speed is worth every cent. Yes the 8-speed is much better at handling the gearing needs of a Jeep with that deep 5-1 first gear. It also runs a very tall 8th gear, higher than any other year I believe.

I did go 5.38 with 35” tires. Maybe a bit tall but in no way does it feel overspun at highway speeds given the 8th gear ratio. I have the full use of the transmission, an additional 30% increase in torque multiplication, and my overall mileage didn’t suffer. (At highway speeds my mileage is slightly down, yet in town my mileage is up actually.) The majority of my driving is in town or off highway.

Hind sight being 20/20, I’d have done 4.88 or 5.13 with 35’s. 5.13 or 5.38 with 37” or greater tires.

(Maybe I should swap these 35” KM3’s out for a set of 37” STT’s?)
 

offcamber

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The 8-speed is worth every cent. Yes the 8-speed is much better at handling the gearing needs of a Jeep with that deep 5-1 first gear. It also runs a very tall 8th gear, higher than any other year I believe.

I did go 5.38 with 35” tires. Maybe a bit tall but in no way does it feel overspun at highway speeds given the 8th gear ratio. I have the full use of the transmission, an additional 30% increase in torque multiplication, and my overall mileage didn’t suffer. (At highway speeds my mileage is slightly down, yet in town my mileage is up actually.) The majority of my driving is in town or off highway.

Hind sight being 20/20, I’d have done 4.88 or 5.13 with 35’s. 5.13 or 5.38 with 37” or greater tires.

(Maybe I should swap these 35” KM3’s out for a set of 37” STT’s?)
I had Toyo Open Country MT 35's then switched to the Cooper STT PRo's 37x13.5. The STT pros definitely ride a lot rougher than the Toyos..
 

DesertsJL

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I had Toyo Open Country MT 35's then switched to the Cooper STT PRo's 37x13.5. The STT pros definitely ride a lot rougher than the Toyos..
Which is why I’ve stuck with the 35” tires for now. The ride from the Mopar lift is great. Probably as good or better than stock. However I don’t want to destroy the ride from a heavy stiff tire.
 

deitrick1

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4.88s with 37s. Hands down. I'm on a 6-speed JLUR with 37s and in 6th I hit around 2.600 RPMs at 80MPH (on flat NJ highways). I'm betting the auto will be even more favorable. My MPG hovers around 16.5MPG with moderate daily driving. If I'm hard on the skinny pedal, I get more like 14MPG. Again, the auto 8-speed should provide better numbers here.
 

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