Am I crazy to go 5.13 gears with JLUR manual on 35s?

[D60]

JFYI, I ran 5.38s on a D44 with heavy bias ply 38s, chromoly axles, ARB front, Detroit rear and 227:1 gearing and wheeled the living piss out of that rig. Granted, it was lighter than a JLUR, but breaking pinions was NEVER an issue in spite of the theory that having chromoly axles would move the weak link to the R&P. I broke 1 axle at the ujoint on that set up (tigged caps) and spun a cap after the weld broke...wheeled it like that 26 weekends per year (often both days) for about 3-4 years.

This whole pinion tooth count thing is overstated. If you set up your gears correctly (I normally set mine up on the tighter side of the spec so the backlash can't cause as much driveline wind up, which IMO, is what generally breaks things anyway)....you don't have that much risk of breaking R&Ps. Besides, it's more likely to break teeth off the ring than the pinion anyway due to the fact that torque multiplication always takes place AFTER the last gear drive.

Oh my god thank you!!!

Once people actually start snapping pinions, let me know. This argument is used all the time trying to claim the 9" is better than a D70 because the pinion is larger.

This is like saying a Kia Sorrento is better than a Wrangler because it has a stronger.....air conditioner button

But OP, no you are not crazy. Worst case you get slightly worse mileage. Might as well go 5% deeper at 5.38

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[Brew211]

Manual Rubi with 37's, I have no issues offroad or on with stock gearing.

 

[Coder]

A good rule of thumb is re-gear to get you back to stock then to compensate for the extra weight of the larger tires by going down to the next gear size. If you apply logic for 35's upgrade to 4.88 for 37's 5.13.

 

[UKCATS]

A good rule of thumb is re-gear to get you back to stock then to compensate for the extra weight of the larger tires by going down to the next gear size. If you apply logic for 35's upgrade to 4.88 for 37's 5.13.

Yep. 4.88’s work perfect with my 35’s.

 

[unsavory]

Thanks everyone for the input. So it sounds like I should figure out if I'm going to go 37s for sure. And if so, I'll go 5.13 and love with them with 35s for now. And if I plan to stay with 35s I'll go 4.88.

 

[mgroeger]

Thanks everyone for the input. So it sounds like I should figure out if I'm going to go 37s for sure. And if so, I'll go 5.13 and love with them with 35s for now. And if I plan to stay with 35s I'll go 4.88.

TONS of people wheel Sports and Saharas with no problem on 35s and whatever 3.xx gears come stock, but they would fair better jumping to 4.10 or 4.88. TONS of Rubis run 35s on 4.10 gears no problem. I know a Rubi running 37s with 4.88s and he loves it, he has a stick, and is a mechanical wizard.
I'd say leave the 4.10s you already have (free) alone for 35s or if you are just dying to spend $1800 for fun then go with 4.88s or even 5.13s if you really feel that is necessary.

 

[anotherWS6]

I can't stand the stock gear ratio with 35s. Rarely sees 5th and 6th is a fantasy.

6th is a fantasy for me with stock wheels and tires.

Not a jeep but I run 35's (315/75/16) on my Silverado. It's a 4l60 so top - 4th gear- is.0.70 compared to the Jeep's 0.72 6th gear. 4.88's in the truck and they made such a huge difference. People said I was crazy since I already had 4.10's.

Anyway, if I were to do it again I would go 5.13's. We seem to get hung up on cruising RPM. There is absolutely nothing wrong with 2,500rpm at 75mph. The 5.3 in my 5,500lb truck has the same problem my Jeep has. While it has plenty of power on paper, it needs to be revved to see the power. When towing it literally feels like hitting a nitrous button once revs climb to 2,700rpm in 2nd and 3rd. That is where the engine makes power. So I am VERY pleased to be at 2,500 at 75 when towing as it makes 4th (top) gear usable. And puts me at about 2,800 rpm at 85. I am never going to go faster than that. I may kiss 100mph every year or two BRIEFLY, so who cares what engine speed I'm at. I spend 99% of my highway driving time between 55-75mph. And I would gear any of my vehicles accordingly.

Since I was a kid I always remember people talking about how low of an rpm they were turning at 60. That isn't reality any more. When engines ran out of breath atg literally 4 grand it may have been, but today's engines require revs to make power. NA engines anyway.

 

[unsavory]

6th is a fantasy for me with stock wheels and tires.

Not a jeep but I run 35's (315/75/16) on my Silverado. It's a 4l60 so top - 4th gear- is.0.70 compared to the Jeep's 0.72 6th gear. 4.88's in the truck and they made such a huge difference. People said I was crazy since I already had 4.10's.

Anyway, if I were to do it again I would go 5.13's. We seem to get hung up on cruising RPM. There is absolutely nothing wrong with 2,500rpm at 75mph. The 5.3 in my 5,500lb truck has the same problem my Jeep has. While it has plenty of power on paper, it needs to be revved to see the power. When towing it literally feels like hitting a nitrous button once revs climb to 2,700rpm in 2nd and 3rd. That is where the engine makes power. So I am VERY pleased to be at 2,500 at 75 when towing as it makes 4th (top) gear usable. And puts me at about 2,800 rpm at 85. I am never going to go faster than that. I may kiss 100mph every year or two BRIEFLY, so who cares what engine speed I'm at. I spend 99% of my highway driving time between 55-75mph. And I would gear any of my vehicles accordingly.

Since I was a kid I always remember people talking about how low of an rpm they were turning at 60. That isn't reality any more. When engines ran out of breath atg literally 4 grand it may have been, but today's engines require revs to make power. NA engines anyway.

Totally agree now that I regeared. I ended up with 4.88, but would go 5.13 with 35s if I were to do it over again. Yes, even the stock gearing on a Rubicon is just too high with stock tires.

People say you should regear to get back to stock ratio. But IMO, the stock ratio was already too high even on the Rubicon.

 

[8flat]

6th is a fantasy for me with stock wheels and tires.

Not a jeep but I run 35's (315/75/16) on my Silverado. It's a 4l60 so top - 4th gear- is.0.70 compared to the Jeep's 0.72 6th gear. 4.88's in the truck and they made such a huge difference. People said I was crazy since I already had 4.10's.

Anyway, if I were to do it again I would go 5.13's. We seem to get hung up on cruising RPM. There is absolutely nothing wrong with 2,500rpm at 75mph. The 5.3 in my 5,500lb truck has the same problem my Jeep has. While it has plenty of power on paper, it needs to be revved to see the power. When towing it literally feels like hitting a nitrous button once revs climb to 2,700rpm in 2nd and 3rd. That is where the engine makes power. So I am VERY pleased to be at 2,500 at 75 when towing as it makes 4th (top) gear usable. And puts me at about 2,800 rpm at 85. I am never going to go faster than that. I may kiss 100mph every year or two BRIEFLY, so who cares what engine speed I'm at. I spend 99% of my highway driving time between 55-75mph. And I would gear any of my vehicles accordingly.

Since I was a kid I always remember people talking about how low of an rpm they were turning at 60. That isn't reality any more. When engines ran out of breath atg literally 4 grand it may have been, but today's engines require revs to make power. NA engines anyway.

Exactly this. Unless you're running a big hemi, all these new engines need much more RPM . I'm amazed at the lack of power this 3.6 has from 750-1500RPM, I think at idle you could grab the crank pulley with heavy gloves and kill the engine...haha

 

[Oletimer]

Im on 4.88s with 35s and wish i had went 5.13. If i knew i was going 37s for sure i would go 5.38 especially if i didn't drive it daily.

 

[twisty]

Totally agree now that I regeared. I ended up with 4.88, but would go 5.13 with 35s if I were to do it over again. Yes, even the stock gearing on a Rubicon is just too high with stock tires.

People say you should regear to get back to stock ratio. But IMO, the stock ratio was already too high even on the Rubicon.

Probably a manual thing. My tj with a manual was the same way.

I have a auto in my rubicon and was going to go 513s while on 37s and my shop begged me not to do it. So I deferred to his expertise and went 488 and thus far I am pretty happy.

As a side note. prior to getting the gears changed out my auto was handling the 37s pretty darn well. I can see why guys just call it good with 410s.

 

[rustyshakelford]

Probably a manual thing. My tj with a manual was the same way.

I have a auto in my rubicon and was going to go 513s while on 37s and my shop begged me not to do it. So I deferred to his expertise and went 488 and thus far I am pretty happy.

As a side note. prior to getting the gears changed out my auto was handling the 37s pretty darn well. I can see why guys just call it good with 410s.

At this stage in the game I’m all for 5.13s in an auto and 37s+. You’ll cruise around 2300 at 70 and have plenty of power to go

Brett

 

[mgroeger]

At this stage in the game I’m all for 5.13s in an auto and 37s+. You’ll cruise around 2300 at 70 and have plenty of power to go

Brett

Manual, 4.88s and 37s are very nice as well. You don't stay in 1st gear long.

 

[rustyshakelford]

Manual, 4.88s and 37s are very nice as well. You don't stay in 1st gear long.

On manuals we go with 5.13s too! My personal JL has the 6 speed and 37s and we’re at 2500 at 70. Plenty of power but you’re right about not staying in 1st long .

Brett

 

[ChattVol]

On manuals we go with 5.13s too! My personal JL has the 6 speed and 37s and we’re at 2500 at 70. Plenty of power but you’re right about not staying in 1st long .

Brett

Based on regear calculators, with 37s, 4.60 gearing would be equivalent to stock. Bump up to 4.88 and its a little stouter than stock. 2500 rpm seems decently high rpm for 70mph...does it drink fuel? Why not go 4.88?

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