Alignment - Caster adjustment

I don’t follow your wording.

If you reduce caster on the upper, the tire moves away from the cab mount.
If you reduce caster on the lower, the tire moves closer to the cab mount.

The lower will have a more significant effect when adjusted but both contribute to alignment and where the tire sits in the wheel well.

 

When you adjust caster on the top or bottom, it directly effects the the other the same amount. You can’t adjust one with affecting the other. Ie. Adjust the top back(positive) it moves the bottom forward. If you adjust the top forward(negative) it moves the bottom back. The top and bottom are connected via a fixed point through the center of the hub. It’s vertical line that pivots, it does not move linearly forward and backward.

 

If you move the top or bottom forward or backward any amount the opposite end move the exact same amount the opposite direction.

 

May have been already said but if you get to much caster you will get bump steer and it will drive like crap. But some still do it to clear larger tires. You want as close to factory setting as possible without rubbing or just trim.

 

Wrong. The lower the caster # the worse your steering feels and bump steer. They’re a plenty of us running 4+ degrees and zero issues. When the caster is low the truck will feel very light or floaty as some describe it and when you hit a bump you will also get they steering wheel bump steer. I don’t recommend more than 4.5 degrees of caster but they’re have been guys that have run a little more than 5. Most trucks run just great with the factory settings, custom alignments like a lot of have take a good tech as so many aren’t used to setting things out of spec.

 

Changing the settings on the upper most certainly does not change the settings on the lower. It does however change the caster angle which is indicated in your photo, which in turn affects camber and toe.

There is not a fixed point in this situation because both the upper and lower are adjustable. There would be a fixed point on stock suspension but that would be the upper ball joint. On stock suspension you can only adjust the lower which means that in order to change the caster angle you have to rotate the lower forward or backward in the wheel well.

Example: Say you want to max out caster on the lower. The rear cams would be pushed out to the exterior of the truck and the front cams pushed in. This would cause the lower ball joint to move forward in wheel well. Because the settings on the upper are already set, the forward movement of the lower ball joint increases the caster angle.

I know this because I’ve done this. When I cut out my old seized lowers and installed new stock replacements I shoved them all the way forward to not only increase caster angle but increase distance to the cab mount. I left my SPC uppers on their default setting of D which is +2° Caster over stock (which is closer to the cab).



Then because camber affects caster (and vice versa) the alignment tech had to bring the cams back from their extreme settings in order to bring it into the specs I asked for.

 

Correct. If using adjustable ucas you can change both with out affecting the other. I was thinking with a fixed upper and adjustable lower like a jba upper. My apologies for that confusion.

 

No worries, I think at this point the majority of this thread has been focused on stock lowers with SPC uppers with varying questions from a variety of users so I totally understand the confusion.

I agree, more caster is better and less causes bumpsteer!

 

OKay. Yeah never had a custom alignment. Bought my stuff at Walmart and my wife installed it for me. Thanks for your expert input I’ll keep it in mind at my next extended warranty tune up at the local dealership

 

So the shop that just did mine got 4.2/4.6 caster so my upper ball joint no longer hits coil spring on droop. The ball joint is now behind the coil. But, in return they said the tire got closer to the cab mount. They said drive it like that for a couple days and tell them if I have any run issues. Does this make sense to have such high caster( like I wanted) and have less cab mount clearance? They set the Spc’s to the A position highest caster position. Idk. I don’t rub but might at steep angles. About half an inch to three quarters clearance

 

Are you sure your balljoint is hitting the spring, it looks like plenty of space there. I run my SPC's at position E and I don't have any contact with the spring. I have 885 springs so maybe they're narrower.

 

Well I had gouge marks on the spring and in the area I’d always have grease on the spring in that spot. I assumed it was hitting on big speed bumps ect. It was real close