Rock Krawler has several lift kits in the 2.5" range to choose from.

The 2.5" Max Travel comes with adjustable LCAs. The X Factor comes with both LCAs and UCAs.

Now I understand the LCAs help you adjust the castor to improve drive quality.

What advantage do I get by replacing the UCAs?

 

This type of question only leads to more questions. What are you going to be doing for off roading, 2 or 4dr, what's your budget, etc. I speak from experience when i say, you will want front lower (at the least) and rear upper or geometry correction brackets. I you can afford it then do it! If not start with the $100 geometry brackets. Is the jeep drivable, sure but is it's flighty as hell with that size lift or bigger with larger tires.

 

One set, either upper or lower, let's you 'tilt' the top or the bottom of axle to change the caster/pinion angles.

Adding the second set allows for more fine tuning, and also let's you move the entire axle forward/backward in the wheel well.

With front lower and rear upper, you are lengthening the control arms, which gives a better range of adjustability than shortening the front upper and rear lower.

Having beefier aftermarket lowers may be a plus for those who play in the rocks. This is why some people will recommend rear lowers.

 

2 Door.
Mostly daily driver. Off road on the weekends - no hard core stuff, however.
I currently have 33" Mickey Thompson ATZ P3s.

Why is it that most lifts that include control arms include front and rear lowers instead of front lowers and rear uppers? Won't the rear lowers correct the geometry in the same way that rear uppers would? I'm not a fan of the geometry correction brackets. It's another stress point that isn't needed and the ones I have seen (AEV) you end up losing ground clearance.

 

There are several directions I can go is my desire is to get a good lift, plus get the adjustability which I THINK I need. I say think, because I am no expert, but I have done my fair amount of reading and talking to other JK owners like yourselves. Thoughts and opinions on these three "packages". All of these are from Northridge4x4 and are based on their packaged deals which include shocks, front and rear bump stops, rear coil wedges, front and coil clips.

1. RK X Factor (The whole enchilada)
Coils; Front track bar; Rear track bar and bracket; Front and rear, upper and lower control arms; Front and rear sway bar links; front and rear brake line extensions;
$1,979.00

2. RK Max Travel
Coils; Front track bar; Rear track bar bracket, Front and rear lower control arms; Front and rear sway bar links; Front and rear brake line extensions
ADD: Rear track bar
$1,609.99

3. RK Flex
Coils; Front track bar; Rear Track bar bracket; Front lower control arms; Front sway bar links; Front brake lines
ADD: Rear track bar; Rear UPPER control arms; Rear brake line extensions; Rear sway bar links
$1,688.98

Each of #2 and #3 gives me some adjustability in the rear. Are uppers preferred over lowers in the rear? Why?

I guess I am trying to figure out if the extra money and the extra aggravation is worth the $300-$400, unless my math is WAY off, which is entirely possible.

 

Why not start with one set of front and one set of rear adj arms, and then decide if you want to add the second sets sometime in the future. (If you don't need to reposition the axles, why spend the extra money up front?)

At 2.5", many people are fine with stock arms/no correction.

 

X2. The stock mod kit and some new shocks will get you started. Everything else can come later.

 

You just asked the same question I started with, which was, why would I need to replace my Upper Control Arms with adjustable ones? If the lower ones will make it possible for me to adjust my castor angle, then why the uppers? The only thing I can think of would be to reposition the axle forwards or back, but i am looking for confirmation. BUT, I've also heard that you should replace the upper rears rather than the lower rears and I'm not sure why one or the other matters.

 

It was noted in my first reply above. Upper and lower do the exact same thing, just backwards from each other. Rear uppers will be lengthened to increase the pinion angle. Lowers will be shortened to increase the pinion angle.

Front lowers and rear uppers typically have a better range of adjustability since you are lengthening, not shortening, (which probably won't matter with only a 2.5" lift).

Uppers may be a bit less expensive.

Aftermarket lowers will be thicker/stronger/beefier than the stock arms, and will take abuse from rocks or whatever better.

Either upper or lower will do the job just fine. I think you are trying to read too much into this decision. At that lift height, you do not 'need' all 4 sets of arms, and the choice of upper or lower won't make any appreciable difference. So just pick a set and go enjoy.

 

I have a 2.5" TF lift. With just the front LCAs (as you wrote, to improve caster). When my front driveshaft failed, I installed an aftermarket one. Because of the design of the OEM front driveshaft, an aftermarket one is bolt-on without need to adjust pinion angle (so Tom Woods advised me, and so it has turned out). The rear driveshaft, however, uses double Rzeppa joints. That means when (if ever) it fails, or when I finally decide I just want a stronger driveshaft, it will be necessary to adjust the pinion angle. At that time I will add rear UCAs, mostly because they are cheaper. At 2.5" of lift, even though the axle shifted slightly forward, it still runs nicely in the wheelwell with no rubbing once I trimed the pinchseam (those who say 35s don't need the pinchseam trimmed are wrong). I use wedges on the rear axle to fix the coil bend (caused the rear coils to hit the rear trackbar until fixed). At 132K miles, I'd say things are working pretty well, though because of the weight I sometimes run (mostly expedition/overlanding trips) I've had to replace the TF rear coils with OME HD rear coils. You can spend more and add all adjustable control arms and make your Jeep that much more complicated to get aligned. If you have a good alignment shop (one used to working with 4WD custom set-ups or you feel confident in what you can do, then go for it. Otherwise, I'd recommend go with the simplest system that will work for you: Front LCAs only.