Suspension geek questions...

[racepar1]

I have a couple suspension questions, one of which applies directly to the s-chasis', and only some real suspension geeks will truly know the answers to.

First off, I plan on building my own roll center adjustable flca's (probably rear too) and I had a question about the tension rods. I was thinking about putting a rod end on the control arm side of the tension rod as well, but I am not sure if that is a good or bad idea though. From the factory the flca/tension rod assembly acts as one solid arm. Adding that extra pivot point will, I think, allow the flca to move in more of a straight up and down arc and will probably reduce some bind. I am not sure if that would be good or bad though. I am curious to see if someone could model the suspension out and see exactly what all would change and whether or not that would be a good or bad thing. I personally do not have the capabilities to really analyze that.


Second, I was thinking about using torrington bearing on the rear springs as well. I would guess that as the spring compresses it will want to rotate some and letting it rotate may allow the spring to work more effectively and may possibly prolong it's life. I would like to know if others think that is a reasonable theory or an unreasonable one.

[Cory]

I use torringtons on the rear springs. For as cheap as they are, I don't see how it could be a bad decision to use them.

[Matt93SE]

for the fronts, I'm going to use the "shoot from the hip" engineering method, but based on what you're describing, I wouldn't worry about it...

The length of either part will not change if you switch to a different type of joint, even if they pivot. Thus, their arc of travel will not change.

I think that's part of the reason the OEM control arm

1) uses a soft rubber bushing to allow the arm to twist at the inner pivot, and

2) is made of a "C" channel instead of a square tube. That leaves enough flexibility for the part to twist and not rip the two fasteners at the end of the t/c rod out of the control arm-- although I've seen that happen many times on S-chassis control arms.

and

3) If you go to rod end/spherical bearing ends on either/both ends of the control arm, the arm will simply pivot in relation to the t/c rod in sympathy.

[Def]

Torringtons on the rear make sense. Springs will want to rotate slightly as they are compressed, and the torringtons eliminate this binding. In theory this translates to less friction and resistance to motion in the suspension reacting to bumps.

I didn't ever do a back to back comparison with putting mine in, but the rear tends to react very well to bumps with the torringtons, tender springs, and no ebrake(I made the mistake of feeling how heavy it is...).

[djsilver]

I put torringtons front and rear and they do help. I started out greasing them but they collected dust so I just run them dry now. I purchased bearings and thrust washers from the local industrial supply house.

You can make FLCA's with adjustable RC by moving the ball joint up and down or by moving the inner pivot up/down but in either case it will also affect your anti-dive geometry unless you move your tension rod pivot point up/down as well. As-built, the FLCA and tension rod don't have anything near the same pivot plane, which means the tension rod twists more than it rotates on it's pivot. Attaching it to the FLCA with a rod-end would keep it from twisting but wouldn't change its arc of motion, or that of the FLCA. One thing to consider is that, with a rod-end attachment point at the FLCA, the tension-rod would place a twisting force on the FLCA under braking that you wouldn't get by placing the rod-end at the normal pivot end of the tension rod like most aftermarket tension rods. The only way to get the FLCA to move straight up and down would be to put the inner pivot points for the FLCA and tension rod in a straight line so that. together, they act like a conventional A-arm.

I'm not a suspension geek but I am a geek just the same....,

[racepar1]

I put torringtons front and rear and they do help. I started out greasing them but they collected dust so I just run them dry now. I purchased bearings and thrust washers from the local industrial supply house.

You can make FLCA's with adjustable RC by moving the ball joint up and down or by moving the inner pivot up/down but in either case it will also affect your anti-dive geometry unless you move your tension rod pivot point up/down as well. As-built, the FLCA and tension rod don't have anything near the same pivot plane, which means the tension rod twists more than it rotates on it's pivot. Attaching it to the FLCA with a rod-end would keep it from twisting but wouldn't change its arc of motion, or that of the FLCA. One thing to consider is that, with a rod-end attachment point at the FLCA, the tension-rod would place a twisting force on the FLCA under braking that you wouldn't get by placing the rod-end at the normal pivot end of the tension rod like most aftermarket tension rods. The only way to get the FLCA to move straight up and down would be to put the inner pivot points for the FLCA and tension rod in a straight line so that. together, they act like a conventional A-arm.

I'm not a suspension geek but I am a geek just the same....,

There will still be a rod end at the normal pivot point so I doubt there will be any additional twisting under breaking. Adding a rod end at the control arm will change something for sure and I want to know what that will be.

[Matt93SE]

Adding a rod end at the control arm end of the TC rod will not change the arc of motion- only stop the control arm itself from twisting..

[RBbugBITme]

.... thats troof Matt... the number of degrees of freedom are technically still the same its just less restrictive.

[racepar1]

.... thats troof Matt... the number of degrees of freedom are technically still the same its just less restrictive.

So then it's still a good idea since it's less restrictive?

[RBbugBITme]

I was picturing a different suspension when I said that but it should still work. However, that odd rigid mount may actually serve a kinematic purpose. I posted something not too many months ago on how OEM suspensions are often designed to flex/force things in certain ways in order to get the kinematics right.

With that said, just lowering the car wacks everything out so whats one more modification right?

[racepar1]

I was picturing a different suspension when I said that but it should still work. However, that odd rigid mount may actually serve a kinematic purpose. I posted something not too many months ago on how OEM suspensions are often designed to flex/force things in certain ways in order to get the kinematics right.

With that said, just lowering the car wacks everything out so whats one more modification right?

That's what I was thinking. There HAS to be something affected by adding that extra pivot point. I suspect that whatever it would do would probably be a good thing, but you never know.

[Matt93SE]

Only thing I can think is that the fixed factory TC rod mount would add a small amount of spring load to the suspension as things change and the bushings/control arm is twisted under compression and droop.

[racepar1]

Only thing I can think is that the fixed factory TC rod mount would add a small amount of spring load to the suspension as things change and the bushings/control arm is twisted under compression and droop.

It is very hard to visualize, I certainly can't quite do it. I agree that the suspension's arc of travel will not change much, but I believe it will change some at higher misalignment angles. The way the suspension reacts within it's arc of travel will change some too. The OE set-up is designed to work as a solid control arm. Adding that pivot point would make that arm no longer a solid piece and that HAS to affect something. I believe that anything that does change will be a positive thing, but I cannot visualize well enough to say that with any real certainty. I doubt it would be a drastic change in the suspension, but small changes can make all the difference in the world. Maybe I'll try to make up a little scale model somehow.

[jmauld]

Why not drop a line from the balljoint with the current setup and record the movement. Then swap to a setup with three heim joints and record the movement again.

That way there will be no speculation.

[racepar1]

Why not drop a line from the balljoint with the current setup and record the movement. Then swap to a setup with three heim joints and record the movement again.

That way there will be no speculation.

If I am going to try to model it out I'm going to scale it down. It would cost way too much to make the full size set-up and then find out that it just doesn't work and start from scratch all over again.