When it comes to the rear suspension on a vehicle, there are many options available. There is the traditional leaf spring configuration, the 2 link (or trailing arm) setup, the 3 link, the 4 bar, and an independent rear suspension. The growth of the hotrod industry, as well as the mini-trucking industry has created a realm in which all of these possibilities are put to use every single day. The most widely used device listed above is the 4 bar suspension. Because this is the most widely used, many people have adopted different ways of configuring the 4 bar suspension on their vehicle. Some of these ways are better than others, while some are, by far, the worst setup to put on a vehicle. Some people believe that it doesn't matter how it's setup. As long as it works, there will not be any problems. A properly setup and installed forward 4 bar will provide optimum performance for the vehicle and its driver.

Flipping through truck magazines, it is obvious by looking at the different rear suspensions that there are a great number of possibilities as far as installing a 4 link suspension. It may not be obvious as to how these 4 bar suspensions perform, and how road and driving conditions affect the vehicle, so it is unfortunate that people flipping through these magazines see these improperly installed 4 bar suspensions, and they have no one to tell them how incorrect the installation is. Nonetheless they go ahead and do it themselves, not thinking twice or applying logic. There are many characteristics that a 4 link suspension has that apply to the vehicle as it is being driven down the road. Depending on the installation, these can be very advantageous, or very disadvantageous. These characteristics include anti-squat, bump or roll steer, roll center, and braking.

From the standpoint of a mini-truck, ie: Chevy S-10, Ford Ranger, owner, anti-squat can be a very important factor when designing and installing a rear suspension. If a person were to view a vehicle from the side as the driver hits the accelerator, he would notice that in most instances the rear of the car dips down. This happens because as the vehicle accelerates, weight is transferred from the front of the vehicle to the rear of the vehicle (Adams). This "dipping down" motion is called squatting. Anti- squat describes the way that the 4 bar is arranged to reverse the weight transfer, or "squatting". Anti-squat can reverse this weight transfer and it can physically raise the rear of the vehicle as it accelerates, rather than make the rear dip down. According to Adams, an experienced and well respected automotive engineer, "An example would be most drag race cars, which have enough anti-squat characteristics to actually raise the rear of the car under acceleration." Anti-squat is a percentage based number. 100% anti-squat means the vehicle will not rise or squat. More than 100%, the vehicle will rise; less than 100%, the vehicle will squat. This is important to a mini-trucker because if he has a heavily lowered vehicle, it is possible to stay extremely low to the ground while accelerating quickly, without having to worry about the rear dipping down and hitting the road, creating a bumpy ride, as well as destroying the road or vehicle. Mini-truckers who are interested in racing with a lowered truck may find this useful because as the vehicle is lifted with anti-squat characteristics, the tires are pushed onto the ground even more, creating more tire contact surface. The tires are pushed to the ground because of that old scientific phrase "for every action, there is an equal and opposite reaction." The rear of the vehicle rises, therefore, pushing the tires to the ground. With 100% anti-squat, the vehicle will not rise or squat at all.

As a vehicle is traveling, it may encounter a hole in the road, or a dip, or maybe even some debris that needs to be avoided. Each of these scenarios will cause the vehicle to do different things as it hits the hole, or swerves to miss the debris. The characteristic that plays a role in this is bump and roll steer. As the vehicle swerves to miss the debris, the body and frame roll, even if it is a slight roll. This causes the rear axle to come out of alignment from driving in a straight path. Bump and roll steer, as defined in Chassis Engineering, "is the amount and direction that the rear axle might cause the car to steer as it moves through its travel." If the vehicle were to have no roll steer, at ride height, the lower links of the 4 bar suspension would be parallel to the ground. Although no roll steer is optimum, if any is to be present, roll understeer is more appropriate (Adams).

As the vehicle makes a turn, left or right, the body will roll. As the body rolls, the tires will stay in contact with the ground, but their alignment will be changed because the 4 bar is changing their path, pulling them closer, or pushing them farther away from the front of the vehicle. This, in effect, causes the rear tires to steer the vehicle. In a roll understeer situation, as the turn is made, the rear tires will counteract the turn. For example, if a right turn is being made, the axle should try and steer the vehicle left. This may not make much sense, but it is better than roll oversteer. Using the previous example, in a roll oversteer scenario, as the vehicle makes its right hand turn, the axle will steer the vehicle towards the right, with the turn. This is bad because the body will roll even more throughout the turn, causing even more roll steer, and eventually the vehicle will be on a path that was not the intended path of the driver. The driver will then have to correct the turn to stay on his desired path (Adams). Broken down a little more, as the driver makes his turn, he will begin to go too far into his turn, and he will have to correct the vehicle by steering the vehicle out of the turn on his own.

Using the examples above, an explanation of roll center can be laid out. Roll center, described by Cauley in his internet article "Roll Center Understood," "is a theoretical point around which the chassis rolls." Compared to the center of gravity of the vehicle, the lower the roll center, the more the vehicle will roll. In order to provide the vehicle with the most dependable handling, a low roll center is optimum (Adams).

Having optimum roll steer, as well as a nicely plotted roll center, and a good anti-squat value, a vehicle can make turns, take corners, or accelerate better than ever. This is ideal for a mini-trucker because he would not have to sacrifice either being low, or driving like a champ. It is quite possible to achieve the best of both worlds, and really it doesn't take much knowledge, just a small amount of research. There are many other characteristics that a rear 4 bar suspension has that play a role in vehicle dynamics; however, the characteristics outlined are some of the more important ones in how the vehicle handles while being driven down the road.