Advice on new tires & spacers

So then SPC's can do this since the ball joint position is adjustable, correct?

I thought JBA's ball joints were also adjustable but they are not.

 

The adjustability of SPCs upper ball joint doesn’t change the fact that, if you want increased caster angle after a lift, you have to relocate/adjust the position of the upper ball joint rearward. I should clarify, before I said the Lower control arm’s ball joint is fixed. That’s actually not true since that’s what the eccentrics are for, but they don’t move the lower ball joint forward enough to guarantee you can get caster within spec after a lift with stock UCAs).

You could theoretically adjust the SPCs ball joint to be in the same place as it is in a stock UCA to keep the tire from rubbing on the body mount, but that would defeat the purpose of getting an after market UCA (to be able to get good caster angles).

Really, the only reason to get any aftermarket UCA is to ensure that your caster angles can stay within factory spec (at least for lifts that aren’t long travel).

But, as mentioned earlier, because the only way to create a higher caster angle is to move the position of the upper balljoint rearward, the overall tire gets moved rearward as well, reducing tire clearance to the body mount.

I have about 2.5in lift, and I decided to keep the stock UCAs. I have no rubbing under full articulation and wheel turn with 285/70-17 K02s. However, this meant that I couldn’t get caster within factory specs. Which isn’t a big deal since it’s pretty close anyway, and I like the spicy steering feel lol.

eta: after thinking about the SPC adjustable ball joint design, I really wonder if it’s a answer looking for a problem. There’s really no reason for it as far as I can tell. Especially because if you wanted higher caster, an aftermarket UCA with a ball joint that is fixed (but relocated further rearward) still allows for a fair amount of increased caster, by using the eccentrics on the lower control arm. Maybe somebody that’s chopped the body mounts wants an extreme amount of caster to justify the the SPCs, but you have to wonder if that’s worth risking the real possibility of frequent ball joint failures experienced with SPCs.

eta number 2: I have to admit that it took me a couple of Tinkerer videos to understand the interplay of all this, so I might be explaining this in an overcomplicated way. But in summary, if you want to reduce possibility/severity of rubbing on the body mount, keep the stock UCAs. But this will be at the expense of caster angle.

 

Can you explain that please? I thought the eccentrics adjust camber by moving the lower control arm (and thus the lower ball joint) towards or away from the centerline of the vehicle. How does eccentrics adjustment affect caster?

 

In an extreme example, if the front adjuster is positioned to pull the front arm of the UCA in towards vehicle centerline, and the rear adjuster to push the rear arm away from the centerline, the lower ball joint will end up moving forward relative to the UCA ball joint.

In reality though, you probably can’t go to that extreme because you may not be able to maintain appropriate toe or camber numbers. But in my case, they were able to get really close to those extremes and still keep other angles in spec.

 

So are you sacrificing camber for the sake of caster?

 

I wouldn’t want to sacrifice toe or camber for caster. Bad camber will affect tire wear and traction, and bad toe might make it wander like an old riding lawn mower. The way the alignment on the 4runner is set up, adjusting the toe and camber will affect caster. If you chase caster at all costs, it’s likely that you’ll throw off the other two angles. So it’s kind of a balancing act. The idea is to maximize caster while still keeping tow and camber in spec. In my case with stock UCAs, I’m under spec in caster, which I don’t think is the end of the world, it just makes the steering a little lighter and a bit more lively.

What I was getting at before is that it isn’t necessary to complicate things by getting SPC brand upper control arms with the troublesome adjustable ball joints just to get high caster numbers, if that’s what you wanted. The “regular” aftermarket UCAs that relocate the top ball joint rearward will still get you more than stock caster angles and are more reliable because they are fixed. The relocated upper ball joint by itself increases caster, and there is probably some additional caster adjustment possible at the LCA before it begins to throw off toe or camber.

 

Have you seen Kai's explanation of SPC adjustability at 7:53? He talks about being able to move the wheel forward in the wheel well for body mount clearance while maintaining stock caster angles and having camber adjustments independent of caster. I'm not sure about the exact caster numbers he's talking about but it sounds like it would meet minimum spec, yet still move the wheel forward.

He also mentioned the Accutune UCA and how it was designed to optimize alignment numbers and clear the body mount with 33's but details were scarce on this one.

https://youtu.be/huMztKaHsUE?si=wLWgI0RK0ZG6K4xf

 

For those running the MT Baja Boss, how’s road noise as they wear? Also how do they do in snow?

 

I see what you mean…if you max out the LCA so that it is as far forward as possible, you can use the SPCs adjustability to be able to achieve a lowish, but in spec caster, that is further forward than what you can achieve stock. On a stock UCA, that would normally cause the other angles to be off, but that can be corrected by the camber adjustability of the SPCs…. Interesting.

I’d still be hesitant with the SPCs given their track record, since I’m not sure I’d want to avoid a body mount chop if that meant a higher chance of ball joint failure. Especially once you realize (like I just did at minute 14:20 in the video) that UCAs are primarily dealing with inward loads. And after realizing (like I just did, lol) that you’d find SPCs most useful if you’re using more negative offset wheels…which increase inward loads even more…loads that are being taken by the the adjustable ball joint component of SPC UCAs.

I can watch the same Tinkerer video 10 times and still get more out if it. Good stuff!

 

I have about 9000 miles on my 285’s and so far no road noise from them. I had no issues in the snow with mine so far.

 

A bit louder for me taste, but a heck of a tire on the trail. I guess you can't have it both ways.

 

Great, now I have to get SPCs for my John Deere!!

 

Hate to say it, but yard equipment is the one thing I’ll ignore as long as I can. I could be getting tank slappers at 3mph and I wouldn’t care lol.

 

haha!!

 

Hey, there’s a lot of real world feedback using the Search feature (top right corner) on these tires in threads with MT Baja Boss in the title.
Road noise: amazing
Snow performance: amazing

*edit* Ability to pick up beautiful women who like to wheel: substantially increased

 

I’ve made it almost to the 3000 kilometer shop check-up appointment for SPC UCA’s…keeping ya’ll updated on my build thread re: the 2025 quality…3000 is practically a new record for me on SPC’s lol but this go around they moved away from the telescopic balljoint design entirely and increased joint ball size comparable to a pickup larger than 4r.
You’re absolutely correct about SPC prone to increased inner load (in my case very high from wide wheels heavy tires and -32 offset) but perhaps the SPC adjustable star plate isn’t any less strong than a fixed UCA arm in the same castor position

 

The last point is a myth. Unfortunately, a cool rig with meaty tires only seems to be good at attracting other middle age dudes.

 

Were you able to find out how your previous ones failed? Was it the actual ball? Or did the adjustable thing loosen up?

 

Yes so I retained all my blown out SPC parts.. being in Canada, SPC passes on customs fees to you for warranty replacements and customs bends you over at their discretion (ask me how I know) so I replaced out of pocket (once).. they failed from the nature of the “telescopic” ball design that allows certain movement by design, and the joint as a whole can’t handle the load only once unsatisfactory materials started being used in the factory (COVID-19 years). SPC didn’t have these issues for many years before COVID-19, design was exactly the same.
The adjustable star plate never has been a weak link, the thing is friggin installed with a 32mm socket size nut at a whopping 150ft-lbs torque.

 

This is not not a fact lol
I don’t actually have experience pulling chicks with my 4R, I bought it married and I’m faithful as a legit honest Catholic who passes a lie detector test.

 

They're the best.

So information dense.