Rear suspension redesign, Optimizing a semi-trailing arm suspension Options

[groot]

Finally, I'm actually constructing my rear suspension. This one's been in the works for a long time. I've had the parts, but lacked the mill/TIG time to make it happen. So, I'm starting with the 914 trailing arm instead of the 944 trailing arm (need the TIG for that one since it's alum).

Some background, the SCCA production rules state this under "Unrestricted Suspensions: Suspension Control":

2. Suspension pickup points on the chassis or structure may be relocated and/or reinforced. If such points are relocated to the driver/passenger/trunk compartments, such points and attendant suspension components shall be covered with metal panels.
3. The manufacturer’s original system of suspension, e.g., live axle, swing axle, MacPherson strut, A-arm, etc., shall be retained. The wheelbase of the vehicle shall not be changed or relocated in a fore/aft direction.
4. Suspension bushings are unrestricted. Adjustable spherical bearings or rod ends are permitted on all suspension components.
5. Any anti-roll bar, camber compensating device, panhard rod, watts linkage, and/or other suspension stabilizer is permitted. Attachment points of such components are unrestricted.

So, I can move pickup points, I have to run a semi-trailing arm suspension, but I can add a toe link.

The basic idea is that I can get the camber gain I want by playing with the location of the pickup points of the trailing arm to the chassis, but replacing the bulky semi-trailing arm with rod ends on tubes allowing easy control of static alignment settings. Simple geometry.... But, you're stuck with a crappy toe curve.

What suspension gives an excellent toe curve???? A real trailing arm (no toe change). So, allow the rear suspension knuckle to pivot in toe, but control that toe with an additional link (attached to the chassis in such a way that it mimics a trailing arm). This was the brainstorm that hit me one day.

I gathered all the parts last winter, but spent so much time in AZ for work I didn't get to do the work before the racing season crept up on me.

Here's the work I did this morning. That rectangle stock sticking out will be where I attach my toe link. The semi-trailing arm links will mount on the top and bottom of the knuckle (bearing carrier).

[Thorshammer]

GTP,

The SCCA Rules have some very strong limitations. Most of us can and would change the entire design, but we must keep within the rule structure. IE Semi trailing arm. One problem using the 911 arm is the position of the engine and where the 911 arm would need to attach. Remember the 911 arms attach in an area where the trans width is, we must attach them to an area where the engine width is. This makes the car way too wide when using 911 arms. So this probably won't work.

Also Kevin is trying to change his camber gain while minimizing toe change. which is critical for racing cars. changes in toe which are significant are not good. While an amount of camber gain is very good. We actually would like just a touch more than we have now. And without the amount of toe change.

We appreciate your comments about this. Keep em coming.

Erik