Spring/Damper placement effect and cantilever design

How does spring/damper placement really affect a suspension, and how can cantilever designs best exploit this dynamic?

I'm interested in designing a very compact (independent) rear suspension (primarily to adapt to my 61 Falcon) which will probably be based on some existing design. The more compact, the more self contained, and the less mounting points, the better. Which got me thinking about cantilever coilover setups. I get the basics of why a "wider" spring/damper, better "controls" the suspension, but I'm looking for more insight.

Sooo...

1. Let the Earth be the chassis and I'll be a rod end and start waving a 2x4 around (now it's a control arm). If my buddy, the spring, grabs the other end, together we can control it pretty well. But if my really strong buddy grabs the middle, (instead of the end) I think we also could control it pretty well. Though maybe we could shake it hard enough to make the end flop around! But if we also make the 2x4 from more rigid (heavier) wood so it doesn't flop around, what are we trading here (let's assume my buddy just gets stronger when the wood gets heavier)? I suppose we add weight (stiffness) to get more flexible packaging (wider tires)? In the extreme my friend stands with me and we lose all leverage completely - clearly we shouldn't do that.

2. If we nail another 2x4 to it at an angle to create an a arm - that is, when the arc becomes defined- I think we gain a lot of control. This seems to mitigate some of whether or not my weak friend supports the end or if my strong friend supports the middle. Suddenly the unsprung weight of my 2x4 setup seems significant! I'm under the impression that unsprung weight is a useful consideration, but not that critical.

3. If my buddy, instead of grabbing the end of the 2x4, rather hooks it with a pool net (cantilever pushrod), it seems not as stable as when he was holding it directly. But also this seems to be less important in the case of the a arm (defined arc) arrangement.

4. Finally, if I get a 2x4 that's twice as long, and I stand in the middle, and my friend - the spring - holds the "wrong" end of the control arm (extending the control arm itself for cantilever setup) it seems we could have pretty good control, though again the unsprung weight comes up.

So I guess I want to know how much effect unsprung weight really has, and how much "control" is really lost by moving inboard (and presumably increasing spring rate). Is the answer just, "Go as wide as you can given your packaging constraints. Increase unsprung weight (stiffness) as necessary. Then live with it."?

The more shock movement you have, the better you can control it. You will definitely want to do the math on wheel rate and select your springs appropriately. You can also play games with the linkage to get a rising wheel rate (spring rate increases as the suspension compresses), or get it wrong to have a falling wheel rate. You can add some extra holes in your rocker and be able to change effective spring rate easily. Lots of fun games to play.

In reply to Keith Tanner :

Ok, I get that. More movement gives me more precision. So, a mounting point further out gives me more movement, and also gives me more leverage. I'm curious how much I can "fake it" by adding leverage via cantilever.

I think I see what you mean about getting rising or falling spring rates. I guess that comes from the angle of the cantilever to the spring. Generally, the angle should hover around 90° from the pivot to the "lower" spring mount to the "upper" spring mount. But if this angle is close to 0° you could even get negative spring damping! Wow, cool! Hadn't thought of that!