I've done reading all the threads for gears 4.88 vs 5.13, but I never really found any one saying what rpms are at 70-80mph.
I've got 37's on the jeep with a six speed, I live in west Texas where most of the speed limit is 75 mph, I don't want to over rev the jeep ( not really sure if 3000 rpms is over rev) but I want power and descent mpgs, I also want to pull my 19' boat as well with the jeep it is a daily driver.

I know this subject has been worked over but I don't want to waste money on gearing the redoing it later
I have looked at a couple of charts and they all have different answers please help in my decision

 

My 6-speed with 38's turned 2000 rpms at 70mph with the stock 4.10s, and now turns 2700 rpms at 70mph with 5.13s.

At 75mph i'm now right at 3000 rpms.

If i did it again, and KNEW i would never go bigger than 37s/38s, and it was relatively flat where i was doing the majority of my driving, i'd go with 4.88s. I've cut down on my highway driving lately, and when i do i just keep it at 70mph, so it IS nice never having to downshift anymore to climb hills and such. However, the speed limit here is 70, and most drive 75-80 everywhere---and while the jeep will easily do 75-80 now, it causes a pretty big hit in gas mileage running RPMs that high.

If you want to know what it feels like to have 5.13s on the highway, just drive somewhere in 5th gear. That will be pretty close to the feel you'll have.

-Adam

 

Gas mileage ain't that big a deal but will it hurt the engine too bad running a little above 3000 rpm that's my main concern

 

i'd have to agree with what isolated1523 said. 5.13's will give you more power but, at 70 mph, your rpm's will be in the 3000 range. i live in the hills and so 5.13's are what i went with when running 37's but, if you're on flat ground and mpg is more important, 4.88's might be the way to go.

 

You've mentioned power and towing so you'll probably want to go with a lower gear.

I will say you need to talk to some '12 owners. The gearing plan has changed since the 3.6L Pentastar came out with it's better power and torque curves.

 

Unless he has a new jeep and hasnt updated his profile, then he still has a 2008 and talking to someone with a 2012 will do nothing to help his decision. The new motor/trans is a different animal altogether when it comes to choosing gearing.

-Adam

 

Ok, you got me there. I SWEAR when I read him say at the start of the post it was a 2012 but I'm running on 5 hours of sleep. My bad.

<------Sorry, ignore the sleepy guy.

 

So will it kill the jeep engine to run 3000 rpm say going from Odessa to dallas which takes bout 5 hrs sure it's mostly flat here but I don't want to ruin the engine by running high rpm or will it be fine leaning more towards 5.13 yrs the jeep is 08

 

This is a decent reference for figuring out where your rpms will be near at what tire size to gears ratio. However it does not factor in flat vs hill terrain, among other things.





For example, I have an 08 JKU auto with 35" and 3.73 gears... according to this chart at 70mph I should be at 1730rpm. I'm much higher, closer to 2200.

 

I've looked at that chart and on the one on4lo.com both are a little different not sure which one is closer to being right. That one shows that I'll be under 3000 but most people like you say they are higher