Fiveofun

Is there an ideal RPM to run when towing? I have a 3.8 JKUR auto with 4.10 and 33's. In drive at 65 I'm running 2800 RPM. If I regear I'll be somewhere in the low to mid 3000's. Is 2800 high enough to sustain towing in drive? I'm thinking of a 2500 - 3000 lb pop up camper.

Mr.T

I think it's fine as long as the weight is approximately within the specs in the owners manual. If you're 33's are like mine, rated 32.8", it's only 2% different than stock. It's like having 4.02 gears instead of 4.10 with stock rubi tires (32.2").

nthinuf

It will depend on the terrain and the speed you are trying to hold, but higher rpm's may be hard to avoid.

You didn't mention what ratio you are considering, and whether you are towing with OD On or Off. But, just pulling some numbers off the chart to see a quick comparison:

For a 3.8 auto with 32" (measured height) tires.

4.10's
OD On = 2080 rpm @ 70
OD Off = 3014 rpm @ 70

4.88's
OD On = 2476 rpm @ 70
OD Off = 3588 rpm @ 70

I have a 3.8 4door auto with, at the time, 35's and 5.13's (around 2450 rpm @ 70, per the chart), and towed close to the 3500 lb limit (boat or fully loaded uhaul trailer) for around 10 hours up and down between colorado and texas. I had a tough time holding freeway speeds with od/on on any of the inclines or rolling hill areas, or with any headwind. (so for quite a lot of the trip...) I would regularly find myself pushing the od button and then slowing down to lower the rpm's. Didn't have any problems running 3500+ rpm's with od/off, just a personal preference that I didn't want to be that high.

Fiveofun

I'm considering 5.13's and towing at 65 in drive. Even 4.88's seem like it would result in too high a RPM.

nthinuf

Err, does yours have the OD Off button like my '08? Or does it just decide when to downshift? 5.13's with 33's and Drive (OD On) will put you a bit under 2600 rpm at 70. Not too high, but personal preference. If/when you downshift out of OD, you'll go up to around 3770. Whether or not you downshift will depend on the load, the speed, the terrain, the wind, whatever else. You know your location, hard for me to say.

I have never towed a popup, but I can say that my boat is much more aerodynamic than a big boxy uhaul trailer, and much easier to tow. Holding 65 in OD was much easier than trying to hold it while keeping up with traffic at 75. Hills/inclines, and both headwinds and crosswinds are tough on the OD, plan on dropping out.