Adjustable upper control arm opinions.

[DionR]

This is what I'm here for. Thank you for taking the time to measure and map out the difference between A and FMJ knuckles. I've had a suspicion that the FMJ knuckles have been part of the problem with how bad my car drives. I ran them with the stock uppers, torsion bars, lowers, strut rods, and stock K member with 215/60/15's and with decent alignment specs it was borderline dangerous feeling. It wandered around on the road following ruts and felt disconnected from steering input with a 24:1 manual steering box.

My apologize for distracting you with my responses. I was only speaking to something Blu said and wasn't trying to steer you in a direction to fix your car.

As @72bluNblu said above, the F-Body spindles aren't your issue. The differences I am speaking to is only for (potentially) how the car goes through a corner and probably doesn't affect straight line stability. And it probably isn't a difference anyone is going to notice on the street either. It's much more for a competition situation like autocross or a road course, and while I am comfortable with the direction I am going to go, I'm not saying the car for sure will handle better, worse or the same between the two theories.

Funny thing is, I am maybe struggling with a similar issue with how my car drives. I've put on SPC 1.0 UCA's, a new steering idler, replaced my PS box, checked everything front and back and squared up my alignment (I think) and still feels like something is broke. The only thing I know for sure is that the spindles aren't the problem. And I too am unable to get reasonable alignment numbers on the PS without the SPC arms or washers between the LBJ and spindle.

 

[DionR]

It should also be noted that the spindle height is not the only difference between the A body spindles and the FMJ (and B body) spindles. This footnote has been lost out of the online article I linked above after all the magazine buy outs and website format changes, but the later spindles also have more build in SAI, and are 3 lbs lighter. The increased SAI also tends to make cars MORE stable, so, the later spindles should cause LESS wandering in a like to like comparison with the earlier ones.
View attachment 1716479307

Interesting. When I measured my F-Body spindle to make my layout, I didn't notice the UBJ hole being further back from the face of the spindle. Assuming that is how they changed the SAI. I will have to look into this further.

The bottom line is, all suspension geometry is a trade off. Improving one thing usually happens at the detriment of another, and car set up, use, and driver preferences end up having a large impact on the "best" geometry.

Completely agree with that. It's one of the reasons I have struggling with a direction, everything affects everything else and I couldn't figure out which way to go.

In my mind, there are two competing branches to "suspension design". I put that into quotes because I'm not truly doing any design work, only modifying the current design to see if I can make it better within my self imposed constraints. Suspension tuning seems to have two camps, one that feels stiff springs and small sway bars are better and the other that favors big sway bars and lighter springs. In the same way, this theory has two camps as well, one that favors a low roll center and the other that favors a short roll couple. In the end, I am settling into the low roll center camp, but I'm not ready to say I am in the right camp and any other designs/ideas are wrong. Only that it's the direction I am going. I have reasons for it, but I don't have application or proof.

I will say that I feel like I am in good company in the camp I have decided to apply for residency in. The guy that finally flipped the switch for me designed the late model GT40 suspension, and as I said above, the companies that I respect as actual handling companies seem to be in that camp as well. Not companies that came up with a suspension kit and want to say it handles better because it has coil overs, but one's that (in my opinion) actually tried to make something that would handle and had that as the focus of the design. Too many suspensions on the market now seem to say they "handle better", or are assumed to, when the reality is that handling wasn't even on the radar until the news release was written and the sales group wanted to use it as bullet point.

I am not saying a short couple suspension design will handle like a boat, nor that a low roll center design will be a sports car in every sense. The difference between the two might not even register on the meter for someone without a ton of experience. Heck, it might not even make a difference to someone with a ton of experience. I think it is the better design, but the real world might shrug and say "big deal". And I am only looking at this in a static view, I have no idea where it would go if I had a dynamic view. All I am settled on is that I think a low roll center has the potential to handle better in a corner, so that is the direction I will be building in.

 

[tcanin00]

No. You have taken the wrong idea from this. Your alignment being off is 100% your problem.

I know it is. My frustration is that after spending the money on good parts, alignment shops in my area won't align an old car. So now I have to buy the tools and learn how to do it. Both of which aren't terrible things, it's just more money and time that I don't have an abundance of.

FMJ spindle geometry has been looked at before, and it improves camber gain. All suspension geometry is a trade off. Ehrenberg initially made similar statements about the FMJ spindles having negative effects, he was thoroughly debunked by Bill Reilly (Reilly Motorsports) in this article with all the geometry numbers to prove it.

Swapping A & B Body Disc-Brake Spindles - Debated Usage


It should also be noted that the spindle height is not the only difference between the A body spindles and the FMJ (and B body) spindles. This footnote has been lost out of the online article I linked above after all the magazine buy outs and website format changes, but the later spindles also have more build in SAI, and are 3 lbs lighter. The increased SAI also tends to make cars MORE stable, so, the later spindles should cause LESS wandering in a like to like comparison with the earlier ones.
View attachment 1716479307

And I run FMJ spindles on my Duster and my Challenger. They do not cause noticeable problems. The difference between the A and FMJ spindles is quite minor, under normal driving conditions it's not a noticeable difference. Which is not to say that some cars might be better off with A-body spindles, although the argument for FMJ/B body spindles definitely improves as you increase the width and grip from your tires.



All good points, and I appreciate the time you've put into plotting all of this out.

That being said, it IS ride height and alignment settings dependent. I know Peter Bergman worked out the RC for his car, and initially found that he was getting a "below ground" roll center. It's why he briefly went to drop spindles on his car before finding the negative effects of those (mostly bump steer) were worse than the RC issue. I believe he went to the 1/2" taller ball joints after that.

The bottom line is, all suspension geometry is a trade off. Improving one thing usually happens at the detriment of another, and car set up, use, and driver preferences end up having a large impact on the "best" geometry.

I had read the discussions and articles on FMJ using spindles in the place of A body ones and how they were better. My luck would be that they're working against my set up. A good alignment will prove if that is the case or not.

 

[tcanin00]

My apologize for distracting you with my responses. I was only speaking to something Blu said and wasn't trying to steer you in a direction to fix your car.

No need to apologize, you posted good information to be considered.

As @72bluNblu said above, the F-Body spindles aren't your issue. The differences I am speaking to is only for (potentially) how the car goes through a corner and probably doesn't affect straight line stability. And it probably isn't a difference anyone is going to notice on the street either. It's much more for a competition situation like autocross or a road course, and while I am comfortable with the direction I am going to go, I'm not saying the car for sure will handle better, worse or the same between the two theories.

Funny thing is, I am maybe struggling with a similar issue with how my car drives. I've put on SPC 1.0 UCA's, a new steering idler, replaced my PS box, checked everything front and back and squared up my alignment (I think) and still feels like something is broke. The only thing I know for sure is that the spindles aren't the problem. And I too am unable to get reasonable alignment numbers on the PS without the SPC arms or washers between the LBJ and spindle.

There isn't enough adjustment in the SPC uppers? That defeats the purpose of adjustable uppers.

 

[DionR]

There isn't enough adjustment in the SPC uppers? That defeats the purpose of adjustable uppers.

Sorry, I meant I couldn't get much negative camber with the stock arms. As I understand, that is one you problems as well.

With the SPC arms, I have 5 degrees caster and -1.0 degrees camber on the PS. Plenty of adjustment.

 

[tcanin00]

Sorry, I meant I couldn't get much negative camber with the stock arms. As I understand, that is one you problems as well.

With the SPC arms, I have 5 degrees caster and -1.0 degrees camber on the PS. Plenty of adjustment.

Ok, that makes more sense.

 

[72bluNblu]

I know it is. My frustration is that after spending the money on good parts, alignment shops in my area won't align an old car. So now I have to buy the tools and learn how to do it. Both of which aren't terrible things, it's just more money and time that I don't have an abundance of.

Welcome to the world of classic cars. Most of the alignment shops won't touch something they can't turn out in 30 minutes, and since none of their "techs" know anything about old cars they can't guarantee that.

Throw in aftermarket parts that they didn't install and they just don't want the liability.

I had read the discussions and articles on FMJ using spindles in the place of A body ones and how they were better. My luck would be that they're working against my set up. A good alignment will prove if that is the case or not.

There's really nothing about the FMJ spindles that would "work against your set up". Certainly not to create the alignment numbers you're getting.

I've been running the FMJ spindles for well over a decade, with a good alignment they do not create the issues you've been having.

 

[tcanin00]

Welcome to the world of classic cars. Most of the alignment shops won't touch something they can't turn out in 30 minutes, and since none of their "techs" know anything about old cars they can't guarantee that.

Throw in aftermarket parts that they didn't install and they just don't want the liability.

Exactly. The same guy that can fail my car for state inspection, doesn't know how to align it. Make it make sense.

There's really nothing about the FMJ spindles that would "work against your set up". Certainly not to create the alignment numbers you're getting.

I've been running the FMJ spindles for well over a decade, with a good alignment they do not create the issues you've been having.

I'm just saying that out of frustration, and I've been in that situation before. Felt like I made an educated decision and wound up being the wrong choice. I'll get it figured out once I reorganize the garage and get my car in there.