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Discussion Starter · #1 ·
I'm running a RK Flex lift with 2.5" springs in front and 3.5" springs in back. Running 315's on Quadtatrac Hardrock wheels. Bilstein 5100s and a Fox ATS steering damper. Geo correction bracket and adjustable track bar.

RK lower control arms are installed and have a set of the RK uppers sitting in a box that I got a really good deal on. I also have Adams 1310 driveshafts both front and rear.

I'm running the tires at 30 psi after playing around with pressures, I feel like this gives me the right balance of predictably handling versus roughness.

I do feel that my steering is a bit flighty and does not recenter properly. If I take my eyes off the road for a spit second, I can easily be 1/2 way into the other lane. This makes for tiring long drives.

I'm headed to the alignment shop today to get the baseline for my settings. With only a 2.5" lift in the front and given the double cardan u-joints, can I bring the caster up (if needed) by just adjusting the lowers, or should I really be installing the uppers so that I can dial in the pinion angle? (how worried should I be about that?)

I ask because I'm heading on a 2,000 mile 3 week road trip in the Jeep in a few weeks and I'm not sure I'll have the time to work on it myself, and not really sure if there is a mechanic in this town that could competently find the right balance of upper and lower control arm adjustments to optimize caster and pinion angle...

Still trying to figure out how to optiomize all these variables...
 

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Discussion Starter · #2 ·
Here are the current alignment settings. I’m having him back the caster down on the drivers side to get the cross caster split biased to the passenger side (RK spec says 0.2 to 0.4)

Also adjusting toe and centering the wheel a bit. We’ll see if that helps.




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Discussion Starter · #3 ·
I think I might have the answer to my own question. I just got done talking with the tech; he just maxed out the adjustment on one of the LCA’s and ended up with 6° of caster on both sides. According to him this was as close as he could get without more adjustment.

According to RK there needs to be a minimum of 3/4” of threads exposed past the jam nut and that’s where the drivers side is now.

Looks like I might need to put on the uppers in order to gain more adjustability.

What I can’t quite understand is why he can’t just take the drivers side down to 5.8 or 5.6 now that he has the passenger side set at 6°. This is all still new to me.


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Have you run it at 6*? Perhaps the flighty steering has been corrected?

I have a similar setup with 35" MTRs, but no correction brackets. ATS set fairly stiff. Drives fine. I *think* castor is close to 6*, and I can check tomorrow.

Mark

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Every Jeep is different, but 6 degrees of caster should be enough to drive right if Toe is set right. Typically 5 - 6 degrees is common.
The axle pretty much connects both sides caster settings, so there is not much, if any, ability to set caster on one side different than the other side.
You can install the upper arms, and they can be used to dial caster in along with the lower arms. But it is odd to need more than what is achievable with the adjustable lower arms.
Is your Jeep sitting rear high? That can have an effect on caster, if the rear is sitting higher than normal caster will be lower than normal.
 

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I'm a little surprised that you feel that it wanders at 5.3-5.1. Anything over 5° and they usually drive well. Does it wander in both directions? Or primarily pull to the right? Have you driven it up around 6° yet?

As for the front pinion angle, the upper control arms will not adjust that. If you add caster, you increase pinion. While you could add a bunch of wheelbase to correct it, just putting on the upper control arms won't.

The axle is a solid piece and any adjustment done on one side will change the other side. You cannot adjust each side independently. Within .1 or .2, it will not change.

Overall, those setting do not look bad...
 

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Stock caster is 4.2 degrees. At 5+ you already have more caster than stock. Not sure why you want more. Also, adding more will increase the angle between your pinion and driveshaft, possibly resulting in driveline vibrations.

I don’t think the wandering feel is due to caster. Check that all your steering linkages are tight. Check your tire pressure. Rotate your tires.

Looks like your toe needs correction.

What kind of tires do you have? Some have a radial pull. Nitto Trail Grapplers, for example, tend to pull left.
 

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The first thing I'd be checking is that all of the suspension and steering part bolts are tight. Get a torque chart and if not previously done, loosen all the bolts with the Jeep sitting on flat ground (not jacked up). Then tighten at ride height.

The wandering would first make me think the track bar isn't tight at one or the other end. Your caster setting should make it center "harder" than stock. I do sort of chuckle about caster being different from one side to the other. I'd certainly want to see that the wheels are all square and centered with those LCAs. That's something you could do in your garage with nothing more than a tape measure.

Getting toe set is about the only thing I see helping at the alignment shop. But you'd want everything else set before getting final alignment done. Front and rear axles centered at ride height, bolts loosened, then torqued. Control arms set for square (measure right front to right rear wheel center, repeat left, they should be exactly the same).

Good luck.
 

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Discussion Starter · #9 ·
Thanks all. Here’s the specs after the work done on it.



It definitely drives better now. No vibrations on the highway that I could discern on my drive home on the fwy.

Maybe the toe was the issue even though the “total toe” was on spec at 0.17 (?). The wheel was apparently off center a bit.

Now running at 6° of caster on both sides. Is that too much? What is the down side? (Excess tire wear?)

Also, if adjustable UCA’s don’t allow for caster adjustment, what do they do? (Strictly for setting position of axle in wheel well ?).

If you were in my situation, would you install them (like I said they are sitting in a box brand new but I don’t want to create other problems. by installing them!)

The problem I was trying to solve was that driving down the highway required constant attention and thousands of constant “micro adjustments” to keep in a straight line. If I reached into the glove box for something, it was easy to find myself practically in the next lane over when I brought my attention back to the road 2 seconds later.

There was noticeable “bump steer” at both low and high speed. For example on the highway the Jeep would tend to lurch and pull whenever it hit uneven pavement, and on city streets exhibited similar behavior, pulling hard when hitting a groove or dimple.

It never felt unsafe, just exhausting after a 6 hour drive.

These symptoms seem to have diminished greatly or possibly disappeared altogether with the new settings.

I’m running KO2s aired at 30 psi cold. The steering damper is adjusted “all the way soft” per some other suggestions I received.


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Thanks all. Here’s the specs after the work done on it.



It definitely drives better now. No vibrations on the highway that I could discern on my drive home on the fwy.

Maybe the toe was the issue even though the “total toe” was on spec at 0.17 (?). The wheel was apparently off center a bit.

Now running at 6° of caster on both sides. Is that too much? What is the down side? (Excess tire wear?)

Also, if adjustable UCA’s don’t allow for caster adjustment, what do they do? (Strictly for setting position of axle in wheel well ?).

If you were in my situation, would you install them (like I said they are sitting in a box brand new but I don’t want to create other problems. by installing them!)

The problem I was trying to solve was that driving down the highway required constant attention and thousands of constant “micro adjustments” to keep in a straight line. If I reached into the glove box for something, it was easy to find myself practically in the next lane over when I brought my attention back to the road 2 seconds later.

There was noticeable “bump steer” at both low and high speed. For example on the highway the Jeep would tend to lurch and pull whenever it hit uneven pavement, and on city streets exhibited similar behavior, pulling hard when hitting a groove or dimple.

It never felt unsafe, just exhausting after a 6 hour drive.

These symptoms seem to have diminished greatly or possibly disappeared altogether with the new settings.

I’m running KO2s aired at 30 psi cold. The steering damper is adjusted “all the way soft” per some other suggestions I received.


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Adjustable lower control arms (and uppers) allow you to adjust caster and pinion angle. Those two setting are adjusted as one, you cannot adjust pinion angle without changing caster using the adjustable control arms. You also can't adjust caster on one side dramatically different from the other side, as caster is based on the rotational angle of the front axle and being made out of fairly stout steel it tends to want to keep both ends of the front axle in the same position relative to each other.
It sounds to me like you could use more Toe.
Is this the first time with the bigger tires? Bigger tires will change the way a Jeep drives, especially the tire width.
Every Jeep is different, but 6 degrees of caster is a lot.
 

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Discussion Starter · #11 ·
Adjustable lower control arms (and uppers) allow you to adjust caster and pinion angle. Those two setting are adjusted as one, you cannot adjust pinion angle without changing caster using the adjustable control arms. You also can't adjust caster on one side dramatically different from the other side, as caster is based on the rotational angle of the front axle and being made out of fairly stout steel it tends to want to keep both ends of the front axle in the same position relative to each other.
It sounds to me like you could use more Toe.
Is this the first time with the bigger tires? Bigger tires will change the way a Jeep drives, especially the tire width.
Every Jeep is different, but 6 degrees of caster is a lot.
Thanks. So do you think there is a compelling reason for me to install these RK UCA's?

You raise a good point about the tires. I bought it with the stock 32s and it handled the same way, but that might have had more to do with the KM2 tread blocks (and over inflation from the dealer) than the alignment. Who knows...

Unfortunately I never had a "baseline" for comparison with this Jeep - it was lifted and modified when I bought it, which was part of its appeal (saved me a ton of money and was done with good (but admittedly not the "best") quality parts). But it means I don't know what "normal" feels like in a JKUR.
 

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Thanks. So do you think there is a compelling reason for me to install these RK UCA's?

You raise a good point about the tires. I bought it with the stock 32s and it handled the same way, but that might have had more to do with the KM2 tread blocks (and over inflation from the dealer) than the alignment. Who knows...

Unfortunately I never had a "baseline" for comparison with this Jeep - it was lifted and modified when I bought it, which was part of its appeal (saved me a ton of money and was done with good (but admittedly not the "best") quality parts). But it means I don't know what "normal" feels like in a JKUR.
I would install them because I have them. If you set their lengths to the stock upper control arm length it will be the same as it was. If you make them slightly shorter you would have more caster (not recommended) and if you make them longer than the stock arms you would get less caster.
Seems like they aren't doing you any good sitting in a box, unless you plan on selling them.
 

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The only thing that really changed with your alignment was the toe. One of your wheels was pretty far off. That’s been fixed and from your comments it sounds like the Jeep drives fine now.

If the question is whether you should install adjustable upper control arms, I think the question to ask yourself is do you need them. Again, it sounds like everything is fine now, so what would be the point?

Contrary to what another poster said, the purpose of adjustable upper control arms is to adjust caster. In your case, you have 6 degrees and wouldn’t want more. So you could install adjustable control arms if you want less caster, which would also decrease the pinion to drive shaft angle. You’d want to consider this if you have driveline vibrations with an aftermarket double cardan driveshaft. If you have no such vibrations, I see no point in installing adjustable arms.
 

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Discussion Starter · #14 ·
The only thing that really changed with your alignment was the toe. One of your wheels was pretty far off. That’s been fixed and from your comments it sounds like the Jeep drives fine now.

If the question is whether you should install adjustable upper control arms, I think the question to ask yourself is do you need them. Again, it sounds like everything is fine now, so what would be the point?

Contrary to what another poster said, the purpose of adjustable upper control arms is to adjust caster. In your case, you have 6 degrees and wouldn’t want more. So you could install adjustable control arms if you want less caster, which would also decrease the pinion to drive shaft angle. You’d want to consider this if you have driveline vibrations with an aftermarket double cardan driveshaft. If you have no such vibrations, I see no point in installing adjustable arms.
Thanks. I have adjustable LCAs (which the tech adjusted to get to 6.0º) but it sounds like the only reason to install the adjustable uppers would be to gain *more* caster, which as you point out, I don't need. So for now, I think they will stay in the box.
 
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