3.6L, 8 AT, 37”: 4.88 or 5.13?

[conFUcius]

The questions I have for those with 3.6L engine, automatic transmission, and 37” tires:

• Did you regear to 4.88 or 5.13 gears?
• Do you regret your choice and wish you’d selected another ratio?
• What do you like most and least about your new gear ratio?
• Anything in hindsight that you wish you’d known beforehand?

I care about having 8th gear back on the highway. My off-roading is usually crawling on rocks, not slogging through mud or blasting through the desert over dunes.

• 5.13s
• No regrets so far. The pinion is a lot smaller but I will just keep that in mind when wheeling to be mindful of that weak point.
• Acceleration around town is decent (I fully acknowledge the Wrangler is not for speed but that doesn’t stop me from desiring it off the line); even with the addition of a steel bumper/winch, still does fine. Highway cruising (70 to 80 MPH) is much smoother since it will stay in 8th and not jump all over the place. The one ‘con’ I could name is fuel economy since I averaged 18 to 20 MPG before and now I’m pretty much around 15 MPG (+/-). Without getting political, this is something one should keep in mind as gas prices rise. Even if money and MPG is not important to you, the frequency in which you have to stop and fill up is an inconvenience too.
• This is less from having the JLU and more from when I had a 6-speed JKU. Know what your final tire size will end up being. I got re-geared in the JKU from 3.73 to 4.56 and was happy with 35s but then I went to 37s and hated being under-geared. Ended up selling it for other reasons but I was basically having to entertain a second re-gear. No one I know said they felt over-geared at any point but there’s anecdotal accounts of people desiring a shorter (numerically higher) gear ratio than they currently have.

Ultimately, you can get by with 4.10s but anyone who does not acknowledge the eventual need to re-gear when on 37s has not personally driven a properly geared Jeep. It’s certainly not the sexiest mod (since you can’t see it) but you won’t regret 4.88s or 5.13s.

Good luck with your decision!

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[Kurt0]

@conFUcius thats honestly why i put on these “oh yeah. Thats in there” haha

i also agree...ive never met anyone who felt they went too deep into gearing either. I went 4.88 over 5.13 because Im not towing, highway drive alot, and want the ability to go back down to 35’s In the future if i need to(i think 5.13/35 WOULD be too deep) I was worried i might regret the 4.88, but so far no...holds interstate speed just fine. That said i wouldnt have been unhappy with 5.13 either i dont think Cant really go wrong with it.

 

[HeavyUser]

Looks like you have your answer, either 4.88 or 5.13 .. .. .. lol

 

[Chocolate Thunder]

Looks like you have your answer, either 4.88 or 5.13 .. .. .. lol

 

[Reseg]

37", 3.6, auto, and 4.88 here. I went to a highly recommended and loved Austin Jeep shop to get a quote for a 5.13 regear and was told to go 4.88. I explained that I didn't care about MPGs or highway cruising, ect... I really was on the 5.13 bandwagon and simply wanted torque lol. They said the only difference it makes is 1st gear, as far as more torque to the ground, and the more extreme I go, the shorter I'm making 1st gear resulting in me shifting out of 1st sooner and then being at a torque disadvantage over the 4.88 until it then shifts into 2nd and the torque advantage then goes back and forth, but is over-all equal (since shifting is based on RPMs and throttle position). They said the 4.88 would easily get me holding 8th as much or more than it did stock, be a stronger pinion, better MPGs, and shift points, and wear and tear closer to stock as it was designed for. I'm not arguing 4.88 is better, just sharing my personal experience and that I'm happy with the 4.88s. I only have a 2-door, and one said "especially since you have a 2-door", so maybe they would've been less pushy for 4.88 if I had a 4-door? dunno.

 

[Chocolate Thunder]

37", 3.6, auto, and 4.88 here. I went to a highly recommended and loved Austin Jeep shop to get a quote for a 5.13 regear and was told to go 4.88. I explained that I didn't care about MPGs or highway cruising, ect... I really was on the 5.13 bandwagon and simply wanted torque lol. They said the only difference it makes is 1st gear, as far as more torque to the ground, and the more extreme I go, the shorter I'm making 1st gear resulting in me shifting out of 1st sooner and then being at a torque disadvantage over the 4.88 until it then shifts into 2nd and the torque advantage then goes back and forth, but is over-all equal. They said the 4.88 would easily get me holding 8th as much or more than it did stock, be a stronger pinion, better MPGs, and shift points, and wear and tear closer to stock as it was designed for. I'm not arguing 4.88 is better, just sharing my personal experience and that I'm happy with the 4.88s. I only have a 2-door, and one said "especially since you have a 2-door", so maybe they would've been less pushy for 4.88 if I had a 4-door? dunno.

Thanks for that. When you’re cruising along in 8th and accelerate hard to pass, do you downshift to 5th or 6th gear? I saw a video that claimed 5.13 would downshift only to 6th in this situation but wouldn’t kick down to 5th.

 

[Kurt0]

 

[Chocolate Thunder]

Thanks. It appeared (not certain) that it stayed in 8th while you had the cruise set at 75? Also have you noticed whether the transmission downshifts all the way from 8th to 5th with brisk passing acceleration or only down to 6th?

 

[Kurt0]

Thanks. It appeared (not certain) that it stayed in 8th while you had the cruise set at 75? Also have you noticed whether the transmission downshifts all the way from 8th to 5th with brisk passing acceleration or only down to 6th?

it stays in 8th readily on the hwy. Obviously bigger hills will see 7th; or lower go up the mountains.

i havent really looked how far it goes down if i stab it to make a pass, but i want to say 6? Ill have to watch

 

[Kurt0]

Thanks. It appeared (not certain) that it stayed in 8th while you had the cruise set at 75? Also have you noticed whether the transmission downshifts all the way from 8th to 5th with brisk passing acceleration or only down to 6th?

tested this 8 times with my pulsar in “stock” setting to try and get you the best answer. The answer is that it depends on your throttle request; so either 6 or 5. From as high as 75mph, rolling into the trottle there was still plenty of head room in 5th to go down that far if you made sufficient throttle request; it would hit approx 4kish and go. Lesser request would get 6th.

hope that helps

 

[Chocolate Thunder]

Thanks, it helps. My concern is whether it is able to still downshift to 5th, as it was stated in a video I saw that claimed 5.13 would only go down to 6th and no lower no matter how much throttle was applied.

 

[Kurt0]

Thanks, it helps. My concern is whether it is able to still downshift to 5th, as it was stated in a video I saw that claimed 5.13 would only go down to 6th and no lower no matter how much throttle was applied.

i gotcha. Hopefully someone with 5.13’s can answer you for sure, but i dont see why it wouldnt. A full throttle request at 75 would be 4500-4600ish in 5th on a 37” tire, so there still enough headroom there.

 

[Reseg]

Okay, tested it out for you on the toll road. Twice I floored it at 70MPH and it kicked down to 4th gear, shifting into 5th at 85mph. 37s and 4.88s, speedo calibrated with my Flashcal and verified by a radar on a 45mph road, multiple times.

 

[Redbaron73]

I never see 8th under 50mph. What does this do for your overall fuel economy? Since upgrading to 37s my JLUR gets approx 280 miles per tank, averaging 14mpg.

@Reseg
Did you have a good baseline of your before and after mpg change?

 

[Chocolate Thunder]

Okay, tested it out for you on the toll road. Twice I floored it at 70MPH and it kicked down to 4th gear, shifting into 5th at 85mph. 37s and 4.88s, speedo calibrated with my Flashcal.

Awesome, thanks. I wonder if anyone with 5.13 gears can chime in with downshift behavior during WOT from 8th gear? The video I saw stated that the transmission wouldn’t go below 6th in this situation. The video was posted by “he who shall not be named here”.

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