As the upper and lower control arms move from full droop to full compression, the rear tires gain a little neg camber and this defines the camber curve. When the trailing arm is inlcuded in this movement, the toe curve is defined. The problem with test this on a stock car is that bushing compliance cannot be factored in unless one can simulate deflection which requires a hell of a lot of force. I've constructed models using tacks as pivot points, cardborad as a hub and straws as the control arms and trailing arm. The straws are the type that have coils so their length can be adjusted. It appears to me the as the rear suspension compresses, the rear wheel toe out a little...not a good thing for stabilty in theory but certainly helpful when turning if the change does not pass some threshold. The full reasoning behind my preference must begin by understanding that I arrived at my camber value by fiddling with the upper and lower control arms so that I have the camber I want while both arms are equal in length. If the top one is shorter or the bottom one longer I believe the camber and toe curves become more aggressive. That's why I prefer to have toe adjusted at the trailing arm. So my camber value out back has basically been stock...1.35 degrees neg ~ I just don't know what the rear bushings are doing and these will affect everything I've written and all my assumptions. Also, change the upper link length and camber is altered. I'm trying to preserve the stock camber curve which I think is pretty damn good - according to the fanny dyno.


...with regard to increasing track Kieth...it's a good thing. At the rear if track is increased, roll centers drop and the wheel follows a wider arc. This wider arc softens camber strength, another way of writing that the camber curve is less aggressive. This may mean bad things since as the car leans, a little more neg camber out back during a turn help grip. on the other hand, up front, and assuming you pick the correct camber value, the Mac strut may never reach a positive camber values as it compresses, something mac struts do. This is a Mac strut's major downfall. A double wishbone gains camber up front. The front is tricky however; lower the car will affect RC height as well as the CofG hieght, increasing track will alter RC height, and altering camber will also alter RC location. The trick up front is to maintain some good RC/CofG relationships while increasing the front end's swing arm. The swing arm is defined by the instantaneous center - a point defoned by the intersection of the angle of the lower control arm and the right angle defined by the strut axis. Lowering and adding more neg camber up front will more than like increase the swing arm by a little, and, change the location of the hieght of the pivot point. This last point - no punn - is important becasue it alters the portion of the arc the wheel moves thru and may cause the front wheels to chieve positive camber sooner...I'm playing with this as we speak.

...of course, I could be full of crap too...

 

...correction above - upper link is stock length lower one is not. I continue to write on the fly and the info is not well organized. Since toe movements are important to me, I located the upper link at stock length. I also, as stated above, do not know what the trailing arm bushings are doing under load. Increasing track via these arms may place these bushing under some type of stress or distortion that is not advantageous. I use a 5mm spacer from H&R out back when the 15mm spacers are used up front.