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).

[groot]

Ok, just got back from the dentist (root canal), so I now can get back to work.....

Not to hijack my own thread... but.... Production racing is more about engine than either the driver or the suspension. The next most important thing is the driver.... then it's suspension setup more than design.

I won't list my driving credentials because I think it's a silly discussion. Who cares? I've always said that if I get to the point that I (as a driver) am not getting the most out of my car, I will put someone in it who can.

I am doing this because I want to and it may make my car a bit more driveable and a bit easier on the rear tires. This is why I'm running production in the first place. Finch's car runs on a pretty close to stock suspension and it's very fast. I was inspired by Finch's legal GT2 944, however.



Now, back to the discussion at hand. Sheridan's setup is great for setting STATIC toe. It does nothing for DYNAMIC toe.... (the curve). His setup suffers the same toe curve issue on all semi-trailing arm suspensions. My idea is to control toe dynamically.... it's not a new idea. I've heard of people using compliant bushings and a toe link to deflect them to achieve a similiar results. Sheridan could have taken the next step and still be legal in GT.

Brett-I've come around on the legality of that Sheridan setup....actually a discussion with Finch helped me see the light (IMG:style_emoticons/default/rocking nana.gif)


Now, back to (IMG:style_emoticons/default/welder.gif)