rocNrow

OK, been looking into regearing my JK lately and got a quote for a decent price, but this guy is recommending 5.13's minimum. Most of what I've read hear seems to lean more towards thw 4.88,s in a 6 speed. My JK is my daily driver too, so don't want to overdo it, need to be able to run highway speeds without cranking a ton of RPM, any thoughts?

Cdyspeed

I've got a six speed and I ordered 4.88 I've talked with a few ppl and they seemed to like them with 35's sorry not much help since I don't have mine installed yet

MTH

What size tires do you want to run?

rocNrow

Duh, its early and still on my 1st cup of coffee. Running 35's.

Bonedoc

I'm in a similar situation. I'm putting a 4.5" lift on my JKU and 37's. I have a 6spd and everyone has been saying to go 5.13's.
Like you, my Jk is a daily driver, I drive on the highway and keeping my RPM's from screaming there and mileage as good as possible is important to me.
I don't do any rock crawling...atleast not serious crawling, nothing that 4lo can't handle.
After scouring the forum and starting threads and weighing opinions from others, I decided for MY situation, 4.88's would be better. For others who rock crawl alot or their JK's are not daily drivers can definately see the benefit of 5.13's.
I had already received my Ring and pinions in 5.13 and ended up sending them back to Dave at Northridge to exchange them for 4.88's.
It isn't an easy decision, good luck with it, There is no right or wrong with it...just what works best for you.

lhracing

4.88's will put you at 2755 RPM @ 70 mph, 5.13 will be 2896 RPM @ 70. 4.88's will be just right, 5.13's are too low for a 6 speed.

rocNrow

Tks IH, nice to hear from someone local

Mark Doiron

I did the 4.88s with 35s and think it's great. I don't think that you'd regret the 5.13s, especially if larger tires are in your future, but I think you'd be delighted with the 4.88s, too. Bear in mind that the difference in torque improvement between 4.88s and 5.13s is pretty modest when compared to from typical stock gear ratios to either lower gearset. And either gear ratio is going to place you on a very optimal part of the torque/HP curve when in sixth gear at highway speeds. That means that there won't be a big difference between the 4.88s and the 5.13s when accelerating to pass someone.

I did a pretty comprehensive analysis of those scenarios for my own decision process and found that there was only little gain with the 5.13s. You can do a similar analysis for your situation by using the Jeep 3.8L engine torque/HP curve and the RPMs versus gear ratios charts. All of that can be found on the Internet with a little bit of searching, but let me know if you're interested in doing it for your scenario and need a little bit of help finding the charts.

rocNrow

Thanks Mark, maybe I'm making this into rocket science and just need to stick to the 4.88s. I will do a little research following your recomendations though.

Mark Doiron

Nothing wrong with a good analysis. Here are a couple things that should help ...

https://www.jk-forum.com/forums/uplo...atio-chart.jpg

kandn.com/dynocharts/57-1553_dyno.pdf

On that last chart, note especially when you get to the flat part on the stock torque curve.