Engine RPS's with different axle ratios?

[sidpost]

I am looking at getting a Rubicon or Willys with a manual 6-speed and V-6. I am wanting to get the lowest gear ratio I can live with on stock tires as I plan on doing 35" or 37" tires in the future.

Assuming 75MPH roads, what engine speeds should I expect with the common ratios in the rear end? Specifically, debating Rubicon 4.10's over a Willys 4.56 option. If I retrofit, the 4.88 is an option as well but. a 5.16 seems way too extreme.

FWIW, I'm looking at overlanding, not rock or mall crawling so I need something practical on the Interstate and capable on challenging roads in an "Overland" scenario, not some extreme "King of Hammers" type of event.

TIA,
Sid

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[AnnDee4444]

 

[6.2Blazer]

4LO.com has a calculator where you can play around with gear ratios vs. engine RPM at certain speeds. Here some of my comments.
Believe the 6 speed manual 6th gear ratio is 0.72:1 and using a stock Rubicon size tire of around 33" and running 75 mph. (Please keep in mind that the "true" tire sizes can fluctuate a little and cause small differences in RPM, but this gives you the idea the difference.

4.10 = 2,250
4.56 = 2,500
4.88 = 2,680
5.13 = 2,820

Not completely sure on the options available, but did quick look at the Jeep website. Looks like both the Willy's and Rubicon come standard with 4.10. 4.88 is an option for Rubicons you can pick by itself. For the Willy's, it shows 4.56 as an option but it forces to add the XR package if you select it.

With that said, I don't think 4.88's would be too bad with the stock size tires.

 

[Zandcwhite]

Having owned 2 JLURs and a JT I'll give my 2 cents. Granted these were all autos. If you're only going to 35s I'd stick with 4.56s. If you are going to 37s 4.88s would be better. Both will be geared lower than I'd like running stock 33s. Not terrible, I drive quite a bit faster than 75mph regularly. I believe you can order a Rubicon with 4.88s so that's the route I'd go with a manual.

 

[Vinman]

I ran 5.13’s with 35’s for nearly a year and it was awesome, almost go-kart like. Now with 37’s I still have no complaints.
Fuel economy took about a 5% hit with the new gears then another 5% with the 37’s.
I do usually limit my speed to about 70-75 MPH.

 

[sidpost]

4LO.com has a calculator where you can play around with gear ratios vs. engine RPM at certain speeds. Here some of my comments.
Believe the 6 speed manual 6th gear ratio is 0.72:1 and using a stock Rubicon size tire of around 33" and running 75 mph. (Please keep in mind that the "true" tire sizes can fluctuate a little and cause small differences in RPM, but this gives you the idea the difference.

4.10 = 2,250
4.56 = 2,500
4.88 = 2,680
5.13 = 2,820

Not completely sure on the options available, but did quick look at the Jeep website. Looks like both the Willy's and Rubicon come standard with 4.10. 4.88 is an option for Rubicons you can pick by itself. For the Willy's, it shows 4.56 as an option but it forces to add the XR package if you select it.

With that said, I don't think 4.88's would be too bad with the stock size tires.

Thanks! 4.56 is an option by itself for 2024 JLU Willys. It is also included as part of the Tire/Wheel group option referred to as the "XR" with 35" tires.

 

[Zandcwhite]

Thanks! 4.56 is an option by itself for 2024 JLU Willys. It is also included as part of the Tire/Wheel group option referred to as the "XR" with 35" tires.

Pretty sure you can't get 35s with the manual though unless something changed. Just checked, can't even get the 4.56 gears without the xr, which changes the trans to an auto on the Jeep build site. With a Rubicon you can opt for 4.88s with the manual though. Again, click the xr to get the 35s and the trans switches to auto. With the stock clutch still exploding or catching fire on occasion the manual is still very limited on the build site. Only the v6, no xr, etc.

 

[sidpost]

2024 Rubicon:
POWERTRAIN

• 3.6L V6 24V VVT Engine Upg I with Stop/Start
  • Standard
• 6-Speed Manual Transmission
  • Standard
• 4.88 Rear Axle Ratio
  • $995

2024 Willys
POWERTRAIN

• 3.6L V6 24V VVT Engine Upg I with Stop/Start
  • Standard
• 6-Speed Manual Transmission
  • Standard
• 4.10 Rear Axle Ratio
  • Standard

I went back to my saved build, and sure enough, the Willys gear ratio was changed with one of my options choices. ?

 

[Zandcwhite]

2024 Rubicon:
POWERTRAIN

• 3.6L V6 24V VVT Engine Upg I with Stop/Start
  • Standard
• 6-Speed Manual Transmission
  • Standard
• 4.88 Rear Axle Ratio
  • $995

2024 Willys
POWERTRAIN

• 3.6L V6 24V VVT Engine Upg I with Stop/Start
  • Standard
• 6-Speed Manual Transmission
  • Standard
• 4.10 Rear Axle Ratio
  • Standard

I went back to my saved build, and sure enough, the Willys gear ratio was changed with one of my options choices. ?

Make sure you factor in the $2-3k for a regear (vs the $995 for optional 4.88s) when looking at the price difference. With the locker sensor failures still being fairly common, I'd opt for the factory 4.88s with a warranty. The second you regear most dealers won't warranty your locker as someone else was in your dif. I prefer the front and rear lockers and 4-1 tcase anyway so the rubi was the obvious choice. We went xr on our 2022 as we wanted the auto and find 4.56s low enough with it even now on 39s.

 

[sidpost]

Yes, definitely trying to avoid a regear. That's why I was looking at the 4.56 in the Willys and 4.88 in the Rubicon.

I really want a 6-speed manual so, that makes the Willys pretty DAMN expensive to get a low enough gear ratio to work with my future tire selection. I suspect it is transfer case related to require an automatic transmission and/or the XR package.

 

[Zandcwhite]

Yes, definitely trying to avoid a regear. That's why I was looking at the 4.56 in the Willys and 4.88 in the Rubicon.

I really want a 6-speed manual so, that makes the Willys pretty DAMN expensive to get a low enough gear ratio to work with my future tire selection. I suspect it is transfer case related to require an automatic transmission and/or the XR package.

Transfer case is the same. It's the weak clutch. That's why the lowest torque engine option is the only one ever offered in the JL with the manual. No diesel, no 392, that clutch won't even hold up to the 2.0t. The solution for exploding clutches was literally to de-tune the v6.

 

[sidpost]

Transfer case is the same. It's the weak clutch. That's why the lowest torque engine option is the only one ever offered in the JL with the manual. No diesel, no 392, that clutch won't even hold up to the 2.0t. The solution for exploding clutches was literally to de-tune the v6.

Aren't the Willys 2.73:1 versus the Rubicons at 4.0:1?

Are the clutches really that fragile? ? Maybe I need to look at a Ford Bronco with its 7-speed manual.

 

[Zandcwhite]

Aren't the Willys 2.73:1 versus the Rubicons at 4.0:1?

Are the clutches really that fragile? ? Maybe I need to look at a Ford Bronco with its 7-speed manual.

Correct, which is 1 of many reasons we went Rubicon. I'm guessing the clutch isn't that bad it's probably excessive slipping because people don't know how to drive.

 

[sidpost]

My Honda Accord "Sport" I4M6 has ~135K miles and no clutch issue right now. I grew up on wheat trucks, tractors, and various service pickups so Manual Transmissions, even bad ones, are not a struggle for me to operate for the long haul.

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