38 inch tires with 4.88 or 5.13 ?

Aloy

Aloy

Member
I have a Jeep JT sport with 37s but in the future will move up to 38s. I leave in Florida and won’t do that much off roading. Please help me decide what gear ⚙️ to use 4.88 or 5.13
 
The right ratio is 5.13 but in a Dana 30, the pinion will be very small and therefore, be a weak point. Being that you live in Florida and assuming you won't be pushing your Jeep too hard off road, it is what I would get anyway.
 
I believe all Gladiators have Dana 44s front and rear, or are least M210 and M220 narrow and wide track variants, but regardless I'd agree with Eddie and say youll undoubtedly want 5.13s for ease around town.
 
DirtHeadDavis said:
I believe all Gladiators have Dana 44s front and rear, or are least M210 and M220 narrow and wide track variants, but regardless I'd agree with Eddie and say youll undoubtedly want 5.13s for ease around town.
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Sport with max tow has 44 front and Rubicon has 44 front. Sport (without max tow) and overland do not.
 
WJCO said:
Sport with max tow has 44 front and Rubicon has 44 front. Sport (without max tow) and overland do not.
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Ah I see, max tow seems like a decent investment then if you're cool with skipping lockers. Comes with 4.10s too. Guess I heard wrong.
 
DirtHeadDavis said:
Ah I see, max tow seems like a decent investment then if you're cool with skipping lockers. Comes with 4.10s too. Guess I heard wrong.
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JTDriver said:
All Gladiators have Dana 44, front and back. At least that’s what I read on the window sticker. Max tow and Rubicon come with the wider rear 44 with 4.10s (I think Mojave is the same also).
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This may be correct. I was thinking of the different gear ratio. No more drinking and posting for me.
 
Def 5.13's. I have 4.88's and running 38's on my JT and it hunts on slight hills on HWY so 38's should dial in perfect with 5.13's. Next tire size I'm goign to go down to 37's.
 
I haven't run the numbers for 38"s but have for 37" tires. I got bored, what can I say. Someone check my math please. I started with a baseline of a JK Rubicon with 32" tires. That should yield a circumference of 100.53 inches. There are 63360 inches in one mile so the 32" tire would rotate 630 times over the course of one mile. With a 3.73 gear and no overdrive the engine would make 2351 revolutions in the same mile and 2584 revolutions with a 4.10 gear. A 37" tire has a circumference of 116.24 inches and would rotate about 545 times over one mile. A 4.56 gear with 37"s and no overdrive would result in 2486 revolutions per mile; 4.88 gear nets 2660 engine revolutions; 5.13 = 2796; and 5.38 = 2936 with no overdrive. My JK feels sluggish going up hills with 32" tires and a 373. Truly believe 4.10s would be ideal for street driving with my tires. Easy to run the numbers for larger diameter but that doesn't account for increased tire rotational mass. Just interpolating, I think the recommendation of 5.13 is spot on for 38"s. I'm seriously considering 4.88 for mine when I upgrade to 37"s, but haven't ruled out 5.13 either.
 
RustyNance said:
I haven't run the numbers for 38"s but have for 37" tires. I got bored, what can I say. Someone check my math please. I started with a baseline of a JK Rubicon with 32" tires. That should yield a circumference of 100.53 inches. There are 63360 inches in one mile so the 32" tire would rotate 630 times over the course of one mile. With a 3.73 gear and no overdrive the engine would make 2351 revolutions in the same mile and 2584 revolutions with a 4.10 gear. A 37" tire has a circumference of 116.24 inches and would rotate about 545 times over one mile. A 4.56 gear with 37"s and no overdrive would result in 2486 revolutions per mile; 4.88 gear nets 2660 engine revolutions; 5.13 = 2796; and 5.38 = 2936 with no overdrive. My JK feels sluggish going up hills with 32" tires and a 373. Truly believe 4.10s would be ideal for street driving with my tires. Easy to run the numbers for larger diameter but that doesn't account for increased tire rotational mass. Just interpolating, I think the recommendation of 5.13 is spot on for 38"s. I'm seriously considering 4.88 for mine when I upgrade to 37"s, but haven't ruled out 5.13 either.
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You sound like an engineer.
 
With an .83 overdrive, 32 inch tires and 4.10 gears, the engine will be turning about 2500 RPM at 70 MPH.
With 37 inch tires and 4.88 gears, RPM will be almost 2600 at 70 MPH.
With 37 inch tires and 5.13 gears, RPM will be about 2700 at 70 MPH.
With 38 inch tires and 5.13 gears, RPM will be about 2600 at 70 MPH.
 
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