LCA vs UCA

[gpurp]

Can somebody help me understand what all gets adjusted with the lowers as compared to the uppers? From the posts I'm seeing it appears that a lot of folks are getting their 6 degrees of caster by swapping out the factory lowers with adjustables. However, I'm thinking about upgrading both lowers and uppers at the same time along with a new track bar. If I get both then do I set the UCA to factory length and still only use the LCA adjustment for caster?

I'm considering getting the cheaper upgrades out of the way on my 2dr Sport before I launch off into springs, shocks, wheels, tires etc.... It doesn't wander bad and the angle finder is near 0 degrees so that means close to 6 degrees caster I think. But I'd like to see if I could dial in a half degree more to clean up the little bit of wandering it has.

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[Rock Krawler Suspension]

Can somebody help me understand what all gets adjusted with the lowers as compared to the uppers? From the posts I'm seeing it appears that a lot of folks are getting their 6 degrees of caster by swapping out the factory lowers with adjustables. However, I'm thinking about upgrading both lowers and uppers at the same time along with a new track bar. If I get both then do I set the UCA to factory length and still only use the LCA adjustment for caster?

I'm considering getting the cheaper upgrades out of the way on my 2dr Sport before I launch off into springs, shocks, wheels, tires etc.... It doesn't wander bad and the angle finder is near 0 degrees so that means close to 6 degrees caster I think. But I'd like to see if I could dial in a half degree more to clean up the little bit of wandering it has.

Many companies will provide a recommended starting length for each arm. The idea should be to protect the wheelbase of the vehicle and provide caster correction as well as provide more joint misalignment with less bushing distortion to provide a clean crisp ride quality with predictable handling. Our recommended starting lengths can be found here: http://pureperformancegroupinc.com/hosted/directions/JL_X_FACTOR_SERIES_MID (05-19 Rev).pdf

 

[gpurp]

Assuming all four front arms are bolted up and have been adjusted to the recommended starting lengths then what's the process to get the desired caster and pinion?

 

[rustyshakelford]

Assuming all four front arms are bolted up and have been adjusted to the recommended starting lengths then what's the process to get the desired caster and pinion?

It’s a balancing act. I’ll try to explain as best I can but the folks at RK can hopefully chime in tomorrow to clarify.

In the stock configuration, you can shorten the upper arms and increase your caster or lengthen the bottom. With aftermarket arms it allows much more flexibility. You can use the LCA to push the axle forward a little to keep it centered in the wheel well but in doing so you’d have to correct caster with the uca. Issues are pushing it to far forward when you compress the suspension the axle will shift forward. This could get it into the front bumper depending on configuration.

Back to your question, if you’re using metal cloak and do a true dual lift which comes with the uca. You’d replace the stock ones with theirs. You would make them shorter than stock which will increase the caster. For rock krawler on their base lift, you would increase the LCA which would accomplish the same thing. Why they do things differently is above my skill set but I’ll tell you both ways work.

Brett

 

[Rock Krawler Suspension]

It’s a balancing act. I’ll try to explain as best I can but the folks at RK can hopefully chime in tomorrow to clarify.

In the stock configuration, you can shorten the upper arms and increase your caster or lengthen the bottom. With aftermarket arms it allows much more flexibility. You can use the LCA to push the axle forward a little to keep it centered in the wheel well but in doing so you’d have to correct caster with the uca. Issues are pushing it to far forward when you compress the suspension the axle will shift forward. This could get it into the front bumper depending on configuration.

Back to your question, if you’re using metal cloak and do a true dual lift which comes with the uca. You’d replace the stock ones with theirs. You would make them shorter than stock which will increase the caster. For rock krawler on their base lift, you would increase the LCA which would accomplish the same thing. Why they do things differently is above my skill set but I’ll tell you both ways work.

Brett

We choose to do lower control arms as, to us, it is the correct way. Pulling the top of the axle back with adjustable uppers and stock lowers does create more caster but the whole axle is shifted rearward which can cause a tire interference with the rear of the fender, it will cause the spring seats on the axle to not align properly with the spring seats on the frame, adjustable uppers are more cost-effective but it isn't the "right" way to do things. Adjustable lowers does not have the same negative drawbacks.

@gpurp that answer is an art, you will likely adjust both to do it the right way but most people will adjust the uppers only.

 

[stil2low]

Shortening the uppers with stock length lowers also give it an over bite look. My buddy like his MC kit but hates the look of the axle rolled back and will go to RKs length specs once he gets adjustable lowers

He’s running Metal Cloaks 3.5 Rock sport (blue JL) and I’m running RK’s 2.5 adventure series 2 so I also have the rear uppers but I measured Center to center and I’m almost 2” longer wheel base

 

[Brosef]

goal should be to add longer LCA's to center the axles within the wheel wells (i.e. to get back to factory wheelbase specs). Once that is done, then you adjust the UCA's to correct the caster / pinion angle. pretty simple, and any good off road shop can handle the job

 

[gpurp]

Now that really gives meaning to RK's earlier comment, "The idea should be to protect the wheelbase of the vehicle..." A two inch wheelbase difference is pretty significant. This pretty much validates my idea of installing new adjustable lowers and adjustable uppers at the same time. It seems the lowers are best used set the axle location to center the wheels in the well. And then use the uppers to dial in the caster. I can see how fine tuning is going to be needed since one affects the other. Thanks for the replies!

BTW, I'm digging that ocean blue qeeJ. Is that a special edition or something?

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