4.88 or 5.13 w/37”?

KurtP

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4.56 is the 37 equivalent for stock gears on 33’s. 4.88 is one step, 5.13 is 2. Its about 150rpm more at highway cruise on 5.13 vs 4.88.





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Mr. Wuf

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I’m stuck with this same decision. I’ve had 37s on my automatic Overland with 3.73 gears for several months, and it’s killing me. My Jeep has forgotten it had an 8th gear.

There’s a very slight possibility I may upgrade to 38s down the road, but I will never go bigger than that. I’m at sea level and do mostly highway driving with some beach driving and plan to tow a small boat or jet ski this summer. My sister-in-law is in the mountains, and we visit her about twice a year. I have a 30-minute commute each morning, so I do care about mileage (as much as any Jeep owner could). My local off-road shop recommends 4.88, but I’m torn between 4.88 and 5.13.

Help!
 

KurtP

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I’m stuck with this same decision. I’ve had 37s on my automatic Overland with 3.73 gears for several months, and it’s killing me. My Jeep has forgotten it had an 8th gear.

There’s a very slight possibility I may upgrade to 38s down the road, but I will never go bigger than that. I’m at sea level and do mostly highway driving with some beach driving and plan to tow a small boat or jet ski this summer. My sister-in-law is in the mountains, and we visit her about twice a year. I have a 30-minute commute each morning, so I do care about mileage (as much as any Jeep owner could). My local off-road shop recommends 4.88, but I’m torn between 4.88 and 5.13.

Help!
imo listen to your shop. They know what they run in their jeeps and what people in your area have asked for and been happy or not with...and 4.88 is certainly well within Normal range for 37’s.

if it helps, im going 4.88 for 37. I was originally going 5.13, but after talking to some other users, decided on 4.88. If i lived in the rockies, id probably lean more towards 5.13, but i think 4.88 is sufficient outside of that based on my research. Ill know more when i pick the truck up.
 

jurfie

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I am out of time and need to make a decision, the more I read the more I succumb to analysis paralysis.
Running 37” ridge grapplers with 3.6 and auto trans. Currently about 1500’ above sea level with trips in the future to Colorado and utah hopefully. Very rare towing but occasionally my CJ7 on a car hauler. Not a daily driver but weekend toy and bug out vehicle only.
4.88 or 5.13 ???
I'll just drop this here. I created it using Grimm Jeeper's Gear Ratio site and specifically for the 8-speed 3.6L JL/JT as the other tables out there are for the JK and do not apply.

screen-shot-2019-12-19-at-10-33-48-am-png.png
 

Krobarr

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TR went down to 4.88 and said it was better.

i usually agree with “you cant go to low”, but decided after much deliberation and consideration of pinion head sizes to go with 4.88.
Living in Alberta we’re in winter half the year and wet for another 3rd, lol. So I’m not as concerned about a smaller pinion gear than in a dry Ricky climate. Thanks for your input though.
 

Krobarr

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Went with 4:88 at sea level...couldn’t be happier with the 37s it should come with these from the factory...I would recommend doing it even if your running 35s
See now I’m in Edmonton, Alberta which is around 2,000 ft (600m) amd I often go towards the Rockies to go wheeling!
 

Krobarr

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I'll just drop this here. I created it using Grimm Jeeper's Gear Ratio site and specifically for the 8-speed 3.6L JL/JT as the other tables out there are for the JK and do not apply.

screen-shot-2019-12-19-at-10-33-48-am-png.png
Appreciate it, I’ve seen a few charts and eventually plan to go larger tires, so I’m happy with my decision to go 5.13, now I just need to get them installed. Being unemployed makes it difficult to allocate the funds:(
 

jurfie

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Appreciate it, I’ve seen a few charts and eventually plan to go larger tires, so I’m happy with my decision to go 5.13, now I just need to get them installed. Being unemployed makes it difficult to allocate the funds:(
No prob. Sorry to hear about being out of work; hopefully you'll find something soon. Sending good vibes to my Albertan neighbour!
 

Krobarr

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No prob. Sorry to hear about being out of work; hopefully you'll find something soon. Sending good vibes to my Albertan neighbour!
Should be back to work in the next two weeks in FMac. So gears are in and I’m loving it in 8th gear all day! However, my lockers have malfunctioned and I’m going to be dropping my fluids and pulling the magnetic sensor out and cleaning it off as I’ve read that some magnetic particles can apparently interfere with the sensor. Will let you all know if that’s the problem.
 

KurtP

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just finished a mostly interstate and highway (with stoplights) route i frequently drive.

3” lift, 37’s, 4.88’s, 3 occupants, 400lbs of cargo from northern MD to central VA.

203.7miles. Displayed MPG 19.7; hand calc was 20.6.

7th was frequently used on hills, but nothing i to 6th i can recall that wasnt speed related. So, i expect it to go to 7th time to time for hills to maximize 8th cruise, as it It still overdrive. The trans never felt “busy” or “undecided” about its gear. I found the drive perfect.

given the conditions, the 4.88 gears accounted for passengers, 3” of lift/airdrag, and 400lbs of cargo while losing less than 1 MPG along that same route when compared to stock height/37’s/stock gears/no cargo.
 

Krobarr

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So I’ve got my 5.13’s installed and wow, what a difference! Tazer Mini should be in later this week to recalibrate and then I’ll be able to begin seeing correct #’s for fuel mileage. Unfortunately though, my lockers are not working now. They engage, and then disengage I get the Service 4WD system error flashing, forward collision deactivated and traction control deactivated. I changed the fluid after break in and pulled off the Diff covers and cleaned the sensor magnet of a particles and reassembled it, but still no go. I’m thinking the Z-Automotive OEM jumpers might be the only option now, but is there something else I could’ve missed? Has anyone found where to buy new locker sensors or are they still only available with an entire axle?
 

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