Let’s talk suspension

First off, thanks to all of the responses to not only my previous questions, but to the many answers I found in the archive of threads. But I’m still left with some basic questions, which seem to grow in complexity as I dig deeper into the subject. But first a disclaimer – I’m going to make some assumptions, many of which may be wrong. What I’m looking for are the experts to come out of the woodwork and help me get my facts straight. Hopefully this exercise will help others out there who - like me – are just beginning their drag-racing careers.

So let’s begin (and I’ll warn you now, this will take a while) -

I see three major components to any basic Mustang suspension: 1) springs; 2) shocks; 3) control arms (one in front, two in back).

Let’s start with the control arms, particularly those in the rear. I know the stock arms have no adjustment whatsoever. When you buy aftermarket CAs, both the upper and lower can be adjusted. Now, when you adjust the UCA, you are effectively changing the pinion angle, which is necessary to get the best launch. But at the same time, I gather that by shortening or lengthening the UCA, you also change the position of the axle housing (i.e. move it backwards or forwards in the wheel well – if ever so slightly). This is where an adjustable LCA comes in handy – not only can it effect the pinion angle as well, but it puts the axle back in the center, so to speak. How am I doing so far, am I on the right track?

Then there is the spring perch on the LCA. For some brands, this is the only part that can be adjusted, and effectively raises or lowers the car. This helps to adjust the instant center of gravity. But you loose the ability to change the length of the LCA, and thus some of the flexibility in fine tuning the pinion angle (so it would seem to me). Does anyone know of a brand that has adjustments for both the length of the control arm and the spring perch? I can’t seem to find one. I know that this could be accomplished by going with coil-overs, but there doesn’t seem to be a rear conversion available for Tokico shocks (unless someone knows of one that I missed).

The next question is the bushings, from what I can see, these can either be solid, or for lack of a better word, “squishy”. Now a squishy bushing will give a nice Cadilac like ride, but you waste a lot of launch energy compressing the bushing during a launch. A solid bushing won’t compress, but you will have a harsher ride. Of course if things are too solid, then I’d guess you’d start ripping apart the car because there’s nothing there to absorb the energy upon launch. So what is the ideal combo for the control arms (both front and back)?

Next are the springs. I understand the basic principles of a good launch: allow the front to rise slowly, thereby transferring weight to the rear tires. Then you want the front to settle slowly so that the rear doesn’t unload causing tire spin. The rise and fall can be controlled by the struts, and the rear shocks can help prevent squatting. But much of these forces are handled by the springs (yes??); the more energy you can store in the front spring, the easier it is to lift the front of the car and get good weight transfer. But it would seem that the stiffer the rear spring, the better to prevent squatting (and many of you have told me as much). But obviously there’s a limit to how stiff the spring should be – is there a way to determine that limit before-hand, or do you just have to use trial and error?

Now we come to the biggest puzzle for me. I know how much my car weighs, both front and rear. For simplicity, let’s focus on the front. The front of my car weighs 1,774 #, or 887 # over each tire. So let’s say I go with a set of coil-overs up front and select 14” springs rated for 130#. If the springs compress 1” for every 130 #, then my calculations tell me that they’ll compress 887/130 = 6.8” under a static load – that’s half their length. There has to be a limit to how much a spring can compress, or travel. If the spring is too soft, then it will run out of space to travel when you hit a bump, and the remaining energy has to be absorbed by the car. This can’t be good. Also, if you hit a bump on the road and there’s no more spring travel left to absorb the dip or bump, you’re liable to lose control of the car, because you’re now riding on a fixed steel rod (for all practical purposes). So how does one find out what the full travel range is for a spring – can you get this from the manufacturer, or is it common knowledge? How much spare travel do you want to leave in the spring? Certainly this depends on the amount of distance the tire travels into the dip, which will increase the force the car exerts as the dip gets deeper. I know this is a matter of physics - and I doubt many of us here are physicists – but it would be nice to have an idea. Certainly the softer the spring, the easier it will be to lift the car on launch. But again, is this a matter of trial and error?

And the final question of the evening – does anyone know (or have a way to find out) what the spring rates are for stock Mustang springs? I’m interested in the 4-cylinder versus 6-cylinder versus V8 (for Fox bodies). Are they fixed rates, or variable?

I know I asked a ton of questions, and thank you so much for bearing with me. I just want to have a better understanding of what’s going on so that I really do set up the suspension that is best for my car; not only in its slower form now, but as I take it down below the 10s barrier.
 
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