Well, here we are at one of the more challenging parts of the build...and one to the most discussed, argued, and beat to death subjects in car building. My goals were simple. 1) Pick the attributes that are most important to the type of driving I will be doing. 2) Arrive on a design that puts the geometry in a way that meets the criteria for goal #1. 3) Design plenty of adjustability into the system so that changes can be made easily.
Here are some of the values that I chose:
Roll Center - Roughly 1.75" above ground (static)
Equivalent Swing Arm - Set at 105" Can be adjusted between 80" and 150" with shims on the upper control arm
Caster - Adjustable between 0 and 8 degrees
Camber - Adjustable from +2 to -5 degrees
I chose to redo the front suspension for a variety of reasons. The whole front track needed to be widened by 5" to match the rear track from the original kit pieces. The original geometry had excessive camber gain through the suspension travel. Another reason for redesign was the fact that I chose Mustang II spindles and had to compensate for their dimensions. Finally, I did not care for the bracket/mounting system that was designed into the kit. It was a little weak in spots and limited the adjustability of the suspension.
Both are being viewed at what I am planning as an initial ride height.
Here are a few more shots of the whole thing. Keep in mind while viewing that everything is just "mocked up" at this point not all the final fasteners are being used. Some things are missing or the wrong size. That will all be taken care of at final assembly.
Some things of note:
The shock mountings have been moved a little further outward. I did this for several reasons. 1) Putting the bottom mount for the shock further out on the LCA puts less bending stress on the LCA and helps keep the spring rate more effective at the wheel. 2) Putting the top shock mount further out keeps the angle of the shock from getting extreme and increases it's effectiveness throughout the suspension travel. 3) I intend to run this car without swaybars initially and use the spings and shocks only to tune the handling. If you notice, I have made provisions for swaybar links on the LCAs if this does not work out well...
Another thing to notice about the upper shock mounts is the fact that I made them extend all the way to the diagonal braces in the front part of the frame. This was done to counteract any bending forces that would be put on the upper rail as a result of moving the shock mounts outward.
Another notable is that all the new (or existing) mounting points for the suspension are now fully boxed. The lower fronts are not yet, but will be. The reason for this is that the "original" style brackets are cantilevered on either side of the 1" frame tubes. The loads from the suspension arms are being transmitted over the cantilevered part. Over time this could lead to the failure of those brackets. Better safe than sorry here.
1/20/07 - Inexpensive DIY Front Alignment.
Since the car is nearing completion, it seemed like a good time to get the front end into the initial alignment settings that I wanted. I was able to set everything up except the toe, but I need to take some material off of the tie rod links to get it adjusted where it needs to be. The whole alignment process was done with a $10 angle finder that I bought at Lowes.
1) Make sure that the chassis is level both fore and aft. I guess if it were not, you could write down the offset value and add/subtract that to the actual camber/castor measurements.
2) Jack up the suspension to the static ride height position. For me, static is having the lower control arms parallel to the ground.
3) Set the camber to the desired angle. I started with -2 degrees. The magnetic angle finder was simply attached to the hub face for setting camber.
4) Set castor to the desired setting. My starting point here was +4 1/2 degrees. On the Mustang II spindle there is a convenient bolt surface near the top that is exactly vertical.
5) Go back and recheck all measurements to make sure that one adjustment did not affect the other.