Ok, I have a '10 jku automatic with 33's that I tow a boat and rzr with pretty regular and I'm fixing to regear and trying to decide which to go with 4.88 or 5.13 any advice which to go with?

 

Have you taken a look at the 3.8L gear charts? The difference between 4.88 and 5.13 will only be ~130 rmp at 70mph. I’d assume your 33’s are really measuring out to 32”. You might take a tape measure to those and verify if you have not already. Is the jeep your DD? Do you ever think you might jump up to a 34 or 35” tire? Typically I’d say that 3.8L needs all the help it can get, and just go for the 5.13; however, the lower you go, the smaller the teeth on the pinion gear are getting. If you have a D30 up front, that may be something you want to ponder, and one thing that could make you lean to 4.88 instead. It just kinda of depends on how you use the jeep. If you’re not wheeling it hard, you might not care about that aspect at all. In all honesty, you’ll be hard pressed to make a bad decision between those two gear sets. You won’t notice this HUGE difference between the two. Rule of thumb is you have to jump 2 gear sets to really tell a significant difference. Whichever you choose will be WAAAAAY better than what you have now if you’re on stock gearing.

 

Do you tow with OD On, or is the load heavy enough (or power weak enough) that you prefer to have OD Off? If you tow OD Off, divide the numbers in the chart by .69 to see where you'll end up.

I have towed my boat and several fully loaded uhaul trailers back and forth from Austin to Denver, and spend much of that time with OD off. 2008 4door with 3.8 auto. Progression from 33's, 35's, 37's, and 3.73, 5.13 and 5.38's. Regardless of gearing or tire size, the engine doesn't have enough grunt to keep me at freeway speeds without kicking in and out of OD. For me, slow and steady with od off beats burning out the trans...

 

I have used the chart and that's how i came up with either the 5.13 or 4.88 i probably won't ever go bigger to a larger tire, I do have the D30 upfront and have looked at getting a new carrier for 3.73 and larger gears. i normally drive at 80 not the 70 that chart goes off of. I have a trans cooler on mine to that runs inline with the radiator. Had i known all of this before buying my jeep i wouldn't have bought the 3.8 or auto i would have gone 3.6 6 speed.

 

Also look at the horsepower or torque curve. My 2012 has the 3.73 gearing and manual trans. When towing, 6th gear doesn't quite have enough HP to keep up at 65mph. However, the 4.10 gears would put me in a power band that has 10% more HP at 65mph. I considered trying to find some 4.10 axles, but instead bought a Tundra with 385hp.

 

Yeah, I wish someone would buy my jeep i would get a truck again.

 

Enjoyment factor of owning a wrangler increases exponentially when it's an extra vehicle, and not a multi-function DD.

 

I agree. Mine is the multi-function DD that gets used mostly for work on and off road. I really need a pickup truck, but can't bring myself to get rid of the JK just yet. It fits like a very comfortable pair of old shoes.

 

I'll sale mine today if someone came to get it.

 

I agree. Mine became an extra vehicle last June. Allowed me to keep the top and doors off all summer since a have the Tundra to drive in the rain. I had to laugh the other day. You may know that I keep detailed records of every gasoline fill up in my Jeep since it was new, 7 years ago. I just got gas a couple of days ago and saw that the last time I had gotten gas in it was November.