Front Control Arm Setup

[GMracer]

I'm building a truck with a ride height of 4.5" and since it's a tube chassis and I'm going to run aftermarket tubular ART arms for that model I was going to raise the mounts to keep the geometry setup better since it's a lot lower than stock. My question is, what is a good basic rule of thumb when it comes to this, should the lower be parallel to the ground at ride height and the upper be different? or all parallel?



I know its not the actual arm being parallel but the imaginary center line from the bolt hole at the frame to the balljoint stud.

[molyorange 77]

I have always heard and read that the lower should be parallel to the ground at ride height.

[GMracer]

what about the upper?

[Twentyover]

My belief if that IN GENERAL the lower is level to droop toward outboard, and upper is droop inboard.

but you really should do some work to see what this all does with negative camber gain in roll and how your FRC migrates around.

Probably suggest you read some Alan Staniforth and build a string computer- you can play with a large number of iterations and science out the geometry on the cheap.

More fundemantally- what do you want the Truck to do?

[GMracer]

handle well, since it will be pretty fast, but I'm still going to bring it up to the drag way for a couple passes, not a full out drag truck it'll have a t56 mated to it, so ideally a street truck.

I'm not sure what you mean by a string computer, I did however order a book on front suspension geometry so hopefully I can get some useful information from there.

My plan was to set up the lower parallel to ride height and the upper pretty close if anything pointing upwards slightly, then move the suspension around and make sure it moves in a fashion that is ideal and call that good. I just wasn't sure if there was a "rule of thumb" for control arm position for cornering that was favored over something else.

Many have told me just to keep the front clip of my frame and build the back half, but I truly don't think having the arms all pointing upwards at ride height is ideal, so I'm modifying.

[John Wright]

Herb Adams has a book called "Chassis Engineering" that should be in your collection. He goes over several key points on suspension and chassis design. Its one of those books where you have to read through a couple of times to grab all of the golden crumbs that fell through when you last read it...LOL

[GMracer]

that is the book I ordered, so good to know. I guess I will find my answer once it comes in, hopefully tomorrow.

[David Pozzi]

It's not going to tell you exactly what to do. It will give some roll center height recomendations and you can design backwards from that.

Generally the lower arm is level, and the upper is angled downward towards the middle of the car by 1.5 to 2 degrees. But this can vary depending on the desired camber gain, or roll center movement desired.

[GMracer]

hmm ok, so it sounds like I got the right idea. I will give this book a good study, thanks guys!