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Are 31 inch tires good on the highway?

Irun

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Pretty sure all 4.0 automatics had 3.73 gears. You can also run a build sheet to check what it left the factory with.

Go here and enter your VIN. Once you do that, you'll see everything your Jeep had originally. That said, a 31" tire will be fine on your Jeep.


FWIW, math is your friend here. A 235/75R15 tire is generally 28.8". A 31x10.50R15 tire is usually 30.5". If you run the gear calculator, assuming a 32RH automatic with 3.73 gears, you get:


28.8" tire = 3046 RPMs @ 70 mph
30.5" tire = 2876 RPMs @ 70 mph

That equals a 170 RPM difference between the two tires @ 70 mph. This is not a significant difference at all. Run a 31" tire and be happy! ;)
 
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machoheadgames

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Pretty sure all 4.0 automatics had 3.73 gears. You can also run a build sheet to check what it left the factory with.

Go here and enter your VIN. Once you do that, you'll see everything your Jeep had originally. That said, a 31" tire will be fine on your Jeep.

[/URL]

FWIW, math is your friend here. A 235/75R15 tire is generally 28.8". A 31x10.50R15 tire is usually 30.5". If you run the gear calculator, assuming a 32RH automatic with 3.73 gears, you get:


28.8" tire = 3046 RPMs @ 70 mph
30.5" tire = 2876 RPMs @ 70 mph

That equals a 170 RPM difference between the two tires @ 70 mph. This is not a significant difference at all. Run a 31" tire and be happy! ;)

I was actually bored yesterday and searched a bunch of autotrader VINs from 97-02 to see what would happen. Majority of 32RH automatics were 3.73, though there were some 3.07s. Most of the autos were Dana 35. The Saharas I checked were all Dana 44, nothing else was. All of the automatics I searched came with 30x9.5 despite 3.07 or 3.73. Of course substitute 3.55 for 3.07 in 97s.

Manuals I found had all of the tire sizes from 215/225/30. More of them were D44s percentage wise than the autos, and they also had 30’s and 3.73s. I did not find any 3.07 30” manuals. The 3.07s were all smaller tires on the manual. There were a decent number of 3.73 Dana 35 upgrades optioned out on both manual and auto.
 

Irun

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I was actually bored yesterday and searched a bunch of autotrader VINs from 97-02 to see what would happen. Majority of 32RH automatics were 3.73, though there were some 3.07s.
Interesting. I've never seen a 3.07 automatic, but guess it could be something as simple as the factory ran out of 3.73 gears and wanted to keep production rolling! :unsure:
 

machoheadgames

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Interesting. I've never seen a 3.07 automatic, but guess it could be something as simple as the factory ran out of 3.73 gears and wanted to keep production rolling! :unsure:

Yeah, no telling. They did the same thing in the YJ. The generally accepted rule was “3.07 manual, 3.55 auto”. I know of multiple 3.07 autos and my manual YJ was 3.55. No Dana 44 option like the 97 3.55s though :cry:
 
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Artsifrtsi

I just wanna go wheeling...
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My ‘05 has 4.0, 6sp, and 3.07’s… drives really well on 31’s, I can pull most of the hills on our highways here in 6th without losing speed.
 

xXDavidCXx

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Interesting. I've never seen a 3.07 automatic, but guess it could be something as simple as the factory ran out of 3.73 gears and wanted to keep production rolling! :unsure:

My 99 was a 3.07 auto.
 

Ourlife Whirlwind

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Pretty sure all 4.0 automatics had 3.73 gears. You can also run a build sheet to check what it left the factory with.

Go here and enter your VIN. Once you do that, you'll see everything your Jeep had originally. That said, a 31" tire will be fine on your Jeep.

[/URL][/URL]

FWIW, math is your friend here. A 235/75R15 tire is generally 28.8". A 31x10.50R15 tire is usually 30.5". If you run the gear calculator, assuming a 32RH automatic with 3.73 gears, you get:


28.8" tire = 3046 RPMs @ 70 mph
30.5" tire = 2876 RPMs @ 70 mph

That equals a 170 RPM difference between the two tires @ 70 mph. This is not a significant difference at all. Run a 31" tire and be happy! ;)

My '02 has the 4.0 engine with the 32RH trans but with the 3.07 gear ratio. I wish it had the 3.73 though.
 
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TheBoogieman

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Interesting. I've never seen a 3.07 automatic
Now you have.
p.s. Can you make my Jeep look as good as yours (for a discount) now. ;)
p.p.s. The 3.07s (and 33s) are why I sold it. Luckily, I found my Rubicon 4 days later.

white jeep good pic.jpg
 
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Pantera99

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Hmmm after reading this thread I suspect I have the 3.07. However most of my driving is highway commuting right now & she's great on the highway. But certainly a dog off the line. 🐕🐶
 

tr21triton

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I have 31's on 4.0 5sp with 3.07's and it does ok up here in the mountains of north Georgia. had 32's when i bought it and it was a slug, but I am looking for somebody selling 4.10/ 4.11's at a decent price. my brothers new 06 RUBI with 33's on 4.10's is a rocket compared to mine !
 

Irun

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Now you have.
p.s. Can you make my Jeep look as good as yours (for a discount) now. ;)
p.p.s. The 3.07s (and 33s) are why I sold it. Luckily, I found my Rubicon 4 days later.

View attachment 357652

It's interesting that there are so many with the 3.07, but I guess with the 32RH it works on the highway. For around town it would suck though. I've just only ever seen the 3.73. I'm wondering if the fact that all the 32RHs I ever had or worked on came with a Dana 44 rear?