We installed 4.88s from a 4.10. (37” tire). Review, tips, and notes inside!

[AZCooWhip]

With what tire size? Just curious

Cooper STT Pros
37x13.5x17

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[Wheelin98TJ]

4.10 w 35's should be right in the sweet spot...should be able to hold 8th at 2000rpm w 75-77mph

The sweet spot for 4.10 is stock Rubi tires.

 

[mrmo]

The sweet spot for 4.10 is stock Rubi tires.

Not w a diesel, maybe w the crappy gas motor

 

[Wheelin98TJ]

Not w a diesel, maybe w the crappy gas motor

The guy you quoted has a gas Gladiator.

If you want to talk about the elite diesel, it helps if you add that info or quote a relevant post.

 

[mrmo]

ok...so

 

[Tim]

4.10 w 35's should be right in the sweet spot...should be able to hold 8th at 2000rpm w 75-77mph

The sweet spot for 4.10 is stock Rubi tires.

Bingo. 4.10s are mostly ok with 35s but they aren't the sweet spot by any means. I think things like wind resistance and overall weight of the truck also come into play. I have a 2 inch lift, a little tire poke, steel bumper, winch and a bed rack. 4.10 is close but not idea. The truck wants to be in 8th most of the time, hence the hunting back and forth between 7th and 8th but it's just a little bit outside of the sweet spot. It's close enough where I wouldn't spend a couple grand to re-gear, though.

I wouldn't even consider 37s unless the truck was getting re-geared at the same time.

I have no interest in getting into a gas vs. diesel debate. Enjoy whichever one makes you happier.

 

[mrmo]

Yep, understand. I was talking about gears for a diesel with the increased torque. Should be right on. No gas/diesel debates from this end....lmao

 

[905_gladiator]

thanks for the write-up, this actually help me decide on gears for my Rubicon on 37's

had 4:88 installed last week at my local 4WP store....they did both the install and the initial break in which was great.

the JT feels better on the highway, around town its great from a dig. Haven't been off-road as yet but I'm sure it will do fine! Not really concerned with MPG its a Jeep its garbage from the onset

with the tazer lite and the z-locker oem installed this thing should last me a while

 

[OngsterA]

I wouldn't even consider 37s unless the truck was getting re-geared at the same time.

Bingo, same thoughts here! I've wheeled on 35s and stock 4.10, no problems no hangups, plus highway trans shifting is still fine. After these KM3s wear out, then will go to 37s AND regear to 5.13 (or maybe 4.88) still deciding what's the best compromise.

 

[scoobycarolanNC]

Gas engine, 4.10s and 37x12.5 Micky Baja Boss M/Ts here. I’m running them at 27psi (they’re a C load not a D like stock). I’m gettin 13mpg on a good day and the highway is mostly 7th gear. Been like this for 6 months and it’s not bad. Wheeled it plenty in 4hi and lo. The only shop around me I trust to regear wants almost 3K so I’m having trouble justifying it.

 

[Slojo]

Bingo, same thoughts here! I've wheeled on 35s and stock 4.10, no problems no hangups, plus highway trans shifting is still fine. After these KM3s wear out, then will go to 37s AND regear to 5.13 (or maybe 4.88) still deciding what's the best compromise.

When I re-geared my JK the shop told me to not spend the money unless you do a 1+ ratio change... in my case I went from the dog 3.23s to 4.10 with 33s. That really woke the engine up some. Going to 5.13 is probably going to make a real difference on 37s.

 

[Bonanza]

Edit 4- Two gas tanks came and went after the oil change. MPGs are.... (drum roll).... 16.7. Literally the same as pre-gearing, to the tenth. I think I'm ready to confirm the disappointment that gears, if just from 4.10 to 4.88, will see little to no gas mileage increase. I was hoping for 1 mpg average, but no matter how I drive, it's not in the cards. Results may differ for the 6 speed, but I think the auto is just that good, as far as compensating for the gearing.

 

[Blade1668]

When I re-geared my JK the shop told me to not spend the money unless you do a 1+ ratio change... in my case I went from the dog 3.23s to 4.10 with 33s. That really woke the engine up some. Going to 5.13 is probably going to make a real difference on 37s.

I have to agree with this logic, when I re-geared my XJ it was 3:54 I went 4:56 it actually put stock speedometer on with 34.5-35 mud tires slightly under speedometer with 33s. But could "break" traction with tires on pavement of sorts un-modded 4.0 or get out of the way pulling into traffic.

 

[Bonanza]

I have to agree with this logic, when I re-geared my XJ it was 3:54 I went 4:56 it actually put stock speedometer on with 34.5-35 mud tires slightly under speedometer with 33s. But could "break" traction with tires on pavement of sorts un-modded 4.0 or get out of the way pulling into traffic.

I'm back and forth about whether or not I should have jumped to 5.13s, My highway cruising RPM is perfect--exactly where I want it. I'd need to drive a similarly equipped 5.13 geared gladiator to know for sure. I just did a long road trip, and my all-highway, up a mountain, down a mountain mpg is 18.3. WIth MT 37s and a 3" lift, I don't think I'll ever get close to stock. It's the city driving that's still at a stubborn 16.7.

 

[Blade1668]

I'm back and forth about whether or not I should have jumped to 5.13s, My highway cruising RPM is perfect--exactly where I want it. I'd need to drive a similarly equipped 5.13 geared gladiator to know for sure. I just did a long road trip, and my all-highway, up a mountain, down a mountain mpg is 18.3. WIth MT 37s and a 3" lift, I don't think I'll ever get close to stock. It's the city driving that's still at a stubborn 16.7.

A detail(s) that is forgot on running really low gears is tooth size on gears and heat build up. So if 4:88 works for you great, only you know what you want or need. A reason "Back in the day" many "up-sized" axles was the tooth size from D44's vs D60/70 and 14 bolt. Not just stronger axles shafts and tubes. Drive 25 miles then change of gear ratio from 3:55 to 4:56 /4:88 and drive same 25 miles, you would find a substantial difference in temperatures. (even after gear break in) The axles (center section) in my XJ ran quite a bit hotter after gear change. You wouldn't want to touch them after HWY driving for some distance especially the D30.

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