Pro Touring 4 link setup

[454SSguy]

For anyone following, found this and helped alot. Just need to measure out the CoG of the truck.

http://mysite.verizon.net/triaged/4l...tml/index.html

[454SSguy]

Alright so I've been doing some researching and have come full circle from thinkin I might want to do a tri 4 link all the way back to the original idea of parallel 4 link and watts link.

Watts link pivot (RRCH) VS CoG line
So I want the RRC pretty low, that makes sense to me, but the question i have is how far is too far. Mainly how far AWAY from CoG line is too far. If the Roll axis is too far from CoG won't that give me LOTS of body roll? Should I make the RRC higher to fix this or keep it down around axle height?

[454SSguy]

No one has input on Roll center height of a truck? ...

[Bryce]

Originally Posted by 454SSguy

Alright so I've been doing some researching and have come full circle from thinkin I might want to do a tri 4 link all the way back to the original idea of parallel 4 link and watts link.

Watts link pivot (RRCH) VS CoG line
So I want the RRC pretty low, that makes sense to me, but the question i have is how far is too far. Mainly how far AWAY from CoG line is too far. If the Roll axis is too far from CoG won't that give me LOTS of body roll? Should I make the RRC higher to fix this or keep it down around axle height?

This all comes back to roll stiffness. Lots of body roll can be reacted with sway bars or stiffer springs.

[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

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.

[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

For anyone following, found this and helped alot. Just need to measure out the CoG of the truck.

http://mysite.verizon.net/triaged/4l...tml/index.html

I use performance trends if you ever need more info than whats in that spread sheet. I also developed my own excel spreadsheet that calculates pick up points based on IC and A/S inputs and two of the four pickup points.