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Discussion Starter · #1 ·
Truck is almost where I want it to be (31.6" tires, 1.5" coilover lift, rear springs replaced, driver side lean resolved , speedometer corrected, no rub anywhere except a little bit on driver side frame when fully locked ) .

The last stage of mods will involve aftermarket UCA install (freedom offroad) + cutting off the droop stop )

Here is my question. I am led to believe that some UCA push the wheel rearward in the wheel well . I am concerned that this might interfere with my mudflaps (as minimal as they are). I have about an inch clearance at worst at the rear of the fender when I turn the wheel . See pic for clearance .

Can anyone comment on how much the wheel is moved backward and will it create issues with rubbing mudflaps. . I could always go SPC but they are kind of expensive right now .

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Most aftermarket UCA's allow for more positive castor, that moves the wheel forward.
 
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2018 Kinetic Blue Ex-Cab ZR2 V6
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Most aftermarket UCA's allow for more positive castor, that moves the wheel forward.
Geometrically speaking, the use of aftermarket UCA's means the wheel can stay centered in the wheel well, while still achieving high positive caster.

As the suspension droops, the UCA swings forward while the LCA stays central, decreasing positive caster. So that means the higher you lift, the less positive caster, since the upper ball joint is now positioned further forward. Here you can see the pivot angle difference between upper and lower control arms. The UCA balljoint travel path is diagonal whereas the LCA balljoint path is vertical.

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To fix this and increase positive caster on stock suspension, you move the lower ball joint forward, which moves the tire forward. But at a certain point you might get maxed out. Aftermarket UCA's with corrected geometry, positions the upper ball joint rearward, which allows you to recenter the lower ball joint to get your adjustment back, while maintaining the high positive caster number. This results in your wheel is back to center in the wheel well.

So technically speaking, geo-corrected UCA's add positive caster while keeping the wheel centered in the wheel well.
 

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Geometrically speaking, the use of aftermarket UCA's means the wheel can stay centered in the wheel well, while still achieving high positive caster.

As the suspension droops, the UCA swings forward while the LCA stays central, decreasing positive caster. So that means the higher you lift, the less positive caster, since the upper ball joint is now positioned further forward. Here you can see the pivot angle difference between upper and lower control arms. The UCA balljoint travel path is diagonal whereas the LCA balljoint path is vertical.

View attachment 434985

To fix this and increase positive caster on stock suspension, you move the lower ball joint forward, which moves the tire forward. But at a certain point you might get maxed out. Aftermarket UCA's with corrected geometry, positions the upper ball joint rearward, which allows you to recenter the lower ball joint to get your adjustment back, while maintaining the high positive caster number. This results in your wheel is back to center in the wheel well.

So technically speaking, geo-corrected UCA's add positive caster while keeping the wheel centered in the wheel well.
So compared to stock, the upper that corrects the caster will actually move the wheel back? Correct?
So it's making the rear well clearance worse? Well the same I guess...
So if you want more clearance in the back of the tire you need a upper that does not correct caster?
 

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2018 Kinetic Blue Ex-Cab ZR2 V6
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So compared to stock, the upper that corrects the caster will actually move the wheel back? Correct?
So it's making the rear well clearance worse? Well the same I guess...
So if you want more clearance in the back of the tire you need a upper that does not correct caster?
Yes and no. The UCA is moving the wheel center back to stock central location in the wheel well. So it's not making things worse, it's making them "stock location"... The point of "correcting geometry" is to bring your upper ball joint back to stock x and z axis (caster and camber) while the suspension is at a lifted ride height, so you don't need to max out your LCA adjustment to achieve appropriate caster.

Realistically, if you need tire clearance that bad, you should be trimming. The caster trick is just a convenient solution that doesn't really negatively impact ride quality.
 

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Yes and no. The UCA is moving the wheel center back to stock central location in the wheel well. So it's not making things worse, it's making them "stock location"... The point of "correcting geometry" is to bring your upper ball joint back to stock x and z axis (caster and camber) while the suspension is at a lifted ride height, so you don't need to max out your LCA adjustment to achieve appropriate caster.

Realistically, if you need tire clearance that bad, you should be trimming. The caster trick is just a convenient solution that doesn't really negatively impact ride quality.
Always been entertaining to me that people are willing to heavily modify suspension geometry/lift with new coilovers, UCA, diff drops, etc... but somehow draw the line at trimming. ???
 

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Discussion Starter · #10 ·
Always been entertaining to me that people are willing to heavily modify suspension geometry/lift with new coilovers, UCA, diff drops, etc... but somehow draw the line at trimming. ???
Trimming is a non reversible , while others mods are , theoretically, reversible . I guess I'll deal with any issues if/as they arise.
 

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Trimming is a non reversible , while others mods are , theoretically, reversible . I guess I'll deal with any issues if/as they arise.
On our trucks it's almost as if GM forgot it would get tires being there is so little room.
You do get better clearance with stock wheels so that's a plus for you.
 
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