Pro Touring 4 link setup

[454SSguy]

Okay, so I've got a few things I'm starting to get a handle on now. I think I understand the RRC. I don't need to worry about calculating it really b/c of the watts link with a chassis mounted pivot. I can just put the RRC anywhere I want correct.

On to the new questions. FRC- from some very basic ideas I've come to the conclusiong that the FRC is lower than the ground. This seems standard on truck applications. I came to this conclusing because of the upward slope (from outside - inside) of the upper control arms puts the Front IC of each side outside the tires. This automatically puts the RC below ground. Please chime in if any of this doesn't sound right.

So control arms are the wrong way, like on older chevelle or other muscle car. What's to stop me from using a set of adjustable control arms and just make a new mount on the frame side whereever I want. It seems like a nice cheap fix to my problem. Build a couple of mounts to hold bushings for the upper arm and set it with the FRC where ever I determine I'd like it (~4" above the ground). I know that it's very rare that a simple solution presents itself so someone please let me know where my thought process is skewed. Other wise I could end up with a truck that could.....turn.
Thanks for the help in advance.

[Bryce]

You are on the right track and moving the UCA mounts down would solve most of the problems and give you camber gain, good thing!

I will answer more in depth, im on my way to work right now.

[454SSguy]

Originally Posted by Bryce

You are on the right track and moving the UCA mounts down would solve most of the problems and give you camber gain, good thing!

I will answer more in depth, im on my way to work right now.

Thanks Bryce, I know trucks have alot of front suspension issues and if it's really this simple to cure alot of them then I'd like to get that info out there for everyone. My few questions I have on the adjustable UCA's like the SPC's are..

1) is it ok to mount them 1", 2", 3" off the frame? How far is too far?

2) I assume I should adjust the camber while I'm there, where do I want it?

3)The angle of the arms top to bottom (as viewed from the front) affects the geometry greatly, what affect do the angle of the arms from front to back (as viewed from the top) have?

4) How much trouble will have I have with my new ball joints/spindles lining up? Will I have to swap spindles? (I would think not, if I just set up my jig from the stock spindle location)

[Bryce]

Originally Posted by 454SSguy

Okay, so I've got a few things I'm starting to get a handle on now. I think I understand the RRC. I don't need to worry about calculating it really b/c of the watts link with a chassis mounted pivot. I can just put the RRC anywhere I want correct.

Yes, the pivot of the watts bell crank is the roll center for the rear suspension. Assuming you have a 3-link, torque arm or parallel 4-link.

On to the new questions. FRC- from some very basic ideas I've come to the conclusiong that the FRC is lower than the ground. This seems standard on truck applications. I came to this conclusing because of the upward slope (from outside - inside) of the upper control arms puts the Front IC of each side outside the tires. This automatically puts the RC below ground. Please chime in if any of this doesn't sound right.

It will also depend on track width and tire diameter and height of the LCA from the ground. I can plot your suspension with my program if you want.

So control arms are the wrong way, like on older chevelle or other muscle car. What's to stop me from using a set of adjustable control arms and just make a new mount on the frame side whereever I want. It seems like a nice cheap fix to my problem. Build a couple of mounts to hold bushings for the upper arm and set it with the FRC where ever I determine I'd like it (~4" above the ground). I know that it's very rare that a simple solution presents itself so someone please let me know where my thought process is skewed. Other wise I could end up with a truck that could.....turn.
Thanks for the help in advance.

[Bryce]

Originally Posted by 454SSguy

Thanks Bryce, I know trucks have alot of front suspension issues and if it's really this simple to cure alot of them then I'd like to get that info out there for everyone. My few questions I have on the adjustable UCA's like the SPC's are..

1) is it ok to mount them 1", 2", 3" off the frame? How far is too far?

I would not space it more than 1/2" due to bolt bending failure. I would run the LCA as long as possible and design the UCA to give the desired amount of camber gain and RC height.

2) I assume I should adjust the camber while I'm there, where do I want it?

Static setup:
I have mine set a -2.5* but I have an autocross car that can drive on the street. But 1* for a street car is normal. But this is going to be dependent on tire wear and overall handling.

Dynamic camber gain:
I setup the camber gain as a function of body roll. First calculate roll stiffness and determine how much body roll in degrees that you have at 1G lateral load. Then calculate the suspension compression at that body roll. Now you want your camber gain to match your body roll. This will ensure your tire has a good contact patch with the ground.

3)The angle of the arms top to bottom (as viewed from the front) affects the geometry greatly, what affect do the angle of the arms from front to back (as viewed from the top) have?

In top view the rotation axis of the control arms will affect caster gain. I like to make the parallel.

4) How much trouble will have I have with my new ball joints/spindles lining up? Will I have to swap spindles? (I would think not, if I just set up my jig from the stock spindle location)

You should be able to use the stock spindles. There might be geometry advantages going to a taller spindle but bumpsteer will also need to be minimized. I like to make sure ball joint is centered (no angle) at ride height, relative to the control arms.

[454SSguy]

Wow, this is alot to take in for sure. I really wish I had access to the truck and could take some measurements.

Ok no crazy spacing on the UCA. That creates some problems. Without shorteing the UCA (which you said to stay away from) the UCA will have to run through the frame. I assume I can do this and just build a hole for each arm of the UCA to move through, but will take up lots of space on the top and bottom of where the frame is now. Doable but definitely on the little bit crazy side,

Another thought on this subject is do I need the UCA and LCA lengths to be the same or the effective lengths. With the UCA and LCA arms the same the UCA will have less effective length b/c it won't be parallel, so should it be longer than the LCA.

For camber angle, I was thinking between -1* and -2*. But I'd like to have a few degrees of adjustment. Any ideas on how to have some adjustability?

I also have a set of drop spindles for the truck. I had planned on not using them since the coilovers drop the truck about 3" in the front, which is not crazy but another 2" on top of that is getting to be alot. On the + side the drop spindles would drop the front but maintain the same suspension geometry, thereby raising the IC's and FRC (still below ground though) and lowering the CoG bringing them closer together. I couldn't say how much really without alot of measuring, which I can't do.

Sorry for the novel.


BTW bryce : Just realized why your name looked familiar. I watched alot of your videos on youtube. You care helped push me "over the edge". LOL Don't worry I won't tell the wife it was your fault.

[454SSguy]

Someone posted this on another forum I'm on. I made a couple of little tweaks to move the camber to -1.5* but left everything else alone. What do you guys think?

http://www.racingaspirations.com/sus...&bhy=250&scl=1

According to that I could see about 1 full degree of negative camber at about 30mm of droop. So I'd want to maybe use a little less static camber or is 2.5* total not to much?

[Barry]

I'm patiently waiting to see some pics of the actual work as I am going to 4-link my Sonoma with coil overs.

[454SSguy]

Well I've been doing some work. I've got the whole 4 link pretty much in but I cheaped out and went with some shorter bars. I don't like how the crossmember sits so I got some longer bars (30") and will be moving the crossmember forward about a foot or so. I'll post up some pics of the progress when I get done.