Tires rubbing cab mounts after UCA

285/70/17

 

What the fuck is going on in this thread?

Positive caster moves your tire forward in the wheel well (towards the front of the truck), not backward. Looking at the pics, your alignment sheet and your cams do not line up, so someone at that shop is bullshitting you, but I think weve established that.

For the record, I have JBAs and 35s on a 2.5" lift and no rub, so i have faith you can fix your setup

 

I think you are mixing up posts from different people.
If you talking to me, I haven’t posted any pics. The alignment tech I use has been doing Offroad trucks for 15 years. I assume he’s good. He told me that 4.5 was as much caster that could be done to my truck. My UCAs are non-adjustable. You think my alignment could still be done better? The guy said that if he put the tire any more forward, that the steering will start pulling to the right.
I know nothing about alignments except for what I read on TW. And there’s a whole bunch of conflicting info on that subject

 

Aftermarket UCA’s adjust caster from the top of suspension, which pushes the wheel back in the wheel well at the top. You can adjust for more caster through the lower control arm which moves the tire forward on the bottom.

 

285s be like.

 

Not sure you understand the geometry. Maybe this will help https://www.quora.com/How-does-the-caster-angle-affect-the-vehicle-dynamics To gain positive caster when are adjusting the upper control arm it has to come back toward the cab. When you gain positive caster from the lower control arm, the tire moves forward. Of course the guy running 35s with only 2.5" of lift with no rubbing should know this.

 

Think about what youre saying because youre actually agreeing with me. Somewhere early in this thread you represented positive castor as this: /. Thats wrong. You also said positive castor moves the wheel back in the wheel well in your first post here. That is *also wrong*. In the most recent post you said to get positive castor you pull the uca back, which IS accurate, but results in your castor angle being like this: \. Since the wheel is at the bottom of that line, it moves forward in the wheel well, not backwards.

So really, what happened here is that you made two contradicting claims within 3 pages. Either way, I understand this, and I couldnt care less as long as OP isnt getting bad information and gets his truck sorted.

 

Your interpretation is backwards, uca caster moves back, lca caster moves forward.

 

Will an illustration help you people? I'm at a total loss as to how this is difficult.



The angle that matters is the difference between the line between your upper balljoint, in your UCA, and your lower balljoint in the LCA, and 90 degrees. If you have positive caster, your lower balljoint is closer to the front of the vehicle than your upper balljoint, and that angle is positive (see illustration).

Therefore, if you move your upper balljoint forward, you are increasing that angle, hence, decreasing caster- read: making it less positive, which *can only* result in pulling the wheel back towards the cab. The only way this is not true is if you also move the lower balljoint forward the same amount or more, which is virtually impossible on our trucks due to the rest of the suspension geometry; the LCAs really only allow for like 4 total degrees of adjustment. The JBA UCAs in question in this thread, which I also own, recognize this limit as well and it's part of the reason they just build ~+2 degrees of caster into the uppers and make them fixed, as you don't gain anything more from having fully adjustable uppers and it just makes alignment techs confused.

Bottom line: it is not physically possible to increase caster without also pushing your tire up in the wheel well towards the front of the vehicle. The opposite has been asserted in this thread and it is false. I have nothing more to say on the matter.

 

It’s your spacers.

 

this guy is the most confused guy here.

 

Yeah, confused about how so many people dont understand something so basic. But it is the third gen forum so...

 

This illustration is 100 percent correct. Being a former certified Toyota technician, the illustration and explanation is spot on. Positive caster move the axis line back on the top and forward on the bottom.

 

So here are pictures of my cam adjusters.
What I am getting is my drivers tire is rubbing on CM when I reverse AND the tires turned to the left. Absolutely no rubbing with right tire.
I have 285/70/17 tires, Icon tubular UCAs, and Fox 2.5 coilovers netting me about 2.25” of front lift.
Before this, I had the same tires, stock UCAs, and OME 887 springs on Bilstein 5100s netting me a hair over 2”. I have no extra weight on the truck.
I had just over 1” of clearance BEFORE and I now have about 2mm of clearance on the drivers side between the tire and CM with the drivers tire turned to the left.
I’m assuming I need to get another alignment.
The alignment tech that did my service said that he couldn’t turn the camber any more positive on the drivers side, unless the vehicle will start pulling to the right.
I really appreciate any and all help with this. Hopefully this might also help the OP and others searching for the same issues.

DRIVERS REAR


DRIVERS FRONT


PASSENGER FRONT


PASSENGER REAR

 

New alignment shop is needed in my opinion. I'm on 295/70/17 with high caster JBAs and I'm just barely rubbing at full lock

I also have about 2" of room behind front wheel sitting leveled and straight. Caster is only at 2.8 as well

However I am on 2.5" of lift up front so it's all relative to the point closest to the truck and height

 

I have plenty of clearance sitting with wheels straight. It’s only an issue with wheels turned to the left and only rubs when in reverse.
By the looks of your picture, I have more room between my tire and CM than you do, sitting with wheels straight.
My wheels are 17x9, -12 offset with 4.5” backspace. That prob has something to do with it also.
By the way, nice looking rig.

 

The difference is, you can only adjust the lower control arm unless you have spc upper control arms. The only adjustment is the lower ball joint. Adjusting for positive caster at the lower ball joint moves the tire forward. Aftermarket upper control arms almost always have positive caster built into them, being the upper ball joint, moves the tire rearward.

 

No. The UCA balljoint moves cabwards to gain caster, nobody is arguing that. But the tire cannot move back in the wheel well and gain positive castor at the same time. Because those two balljoints are connected by a rigid hunk of metal (your spindle), the system pivots. Since your CV sits south of the center of the spindle, any movement cabward at the top of spindle will result in the axle moving towards the front of the vehicle (increasing caster). Like I indicated, the only possible way for the tire to move backwards in the wheel well is for you to decrease castor. For this to not be true, your spindle (read: your steering axis) would have to bend. If that's happening, it's a whole other problem.

Seriously, if this still isn't making sense, put a pencil on your desk, hold it in the middle, and then move one end one direction and watch the other end move the opposite direction. That's whats happening when you modify caster.

edit: also I am so fucking sorry for all the times I've said castor instead of caster. We have moles lol.

 

Well at least Jibbs and I are on the same page.

 

Can someone please explain all of the posts in the SPC UCA’s thread where people actually DECREASED the caster on the adjustable upper ball joint and gained more room between the tire and the cab mount?

https://www.tacomaworld.com/threads...driving-report-with-light-racing-ucas.158795/