Pinion angles should be kept...
Pinion angles should be kept near zero in relation to each other. The reason we would point pinion down a few degrees is to compensate for flex. But you can see from the diagram that the pinion angle can certainly be more than three degrees to be set up right.
Now that the boring part is over, let's get to the subject at hand: suspension design. I am going to describe the major benefits of each design. For a suspension design to be undrivable, it would have to be really bad. Also, if you just can't quite fit the perfect design into your confines, you will have to compromise. That's part of what makes a good fabricator, the ability to adapt to his limitations.
The ladder bar and two-link are both very similar. In fact, a ladder bar is a type of two-link, but not all two-links could be considered ladder bars. The ladder bar design is great for high horsepower, high traction cars that the owner doesn't want to spend the hours or days on it would take to tune a good four-link for the track. The first major downfall of the two-link is that it doesn't allow much articulation (one wheel up and one wheel down). The only way that the design can articulate is to flex a little bit of everything. NASCAR usesa two-link rear suspension that is specially engineered to allow an acceptable amount of flex in order to articulate. The second major issue is pinion angle.The two-link, by nature, cannot keep the pinion parallel to the transmission, so useable travel is limited to the acceptable amount of pinion change. On the other hand, the two-link is fairly easy to tune, to install, and to purchase. Anti-squat is easy to figure because the instant center is the forward pivot. Roll center and roll steer aren't really a concern because the suspension won't articulate, so on the same coin, the need for a sway bar is just not there either. The two-link will require a Panhard bar, track locator, or other similar lateral limiter.
The four-link is separated into three major types:
* Triangulated four-link
* Parallel four-link
* Three-link
Each of these designs has the same advantages and can be oriented as forward, reverse, or "2-forward, 2-reverse." Initially, I am only going to talk about the forward-facing orientation. Once we have described the advantages of those, I will explain the downfall of each of the other orientations. The reason that the three-link is categorized here is that just about every advantage and disadvantage is shared by all three of these systems. In fact, the three-link and parallel four-link are identical except the missing link. It is a space-saver-period.
The way that a link system of this type is drawn out is two-dimensionally, from the side. From that view you cannot tell which design is used. The side view is how you would figure instant center, anti-squat, pinion angle, and a portion of roll steer. Because of the infinite possibilities of the four-link, they are used on just about every straight-axle rear suspension in the performance industry (factory or aftermarket). Good control of the pinion is possible (assuming the designer took it into consideration). They also have infinite instant center options. As a matter of fact, the drag-race community has four-link designs that allow tuning of the instant center separately from one side to the other. Again, the confines and the fear of most builders to "step out of the box" has limited our designs, but the limitations have been on the side of caution. Having an instant center around the front bumper or beyond has very little adverse effect. This is how the manufacturers set up their link systems.