If you're here, you should have down the basic ideas behind air ride suspensions. There is much more advanced ideas beyond the scope of this page, but this is only here to give you a small idea of whats available for you to do and not do.

Rear Suspensions

Here is my research paper on 4 bar suspensions. There is some information regarding the reversing of any of the 4 bar control arms, however it is mainly a topic on forward 4 bar suspensions and some of the charaterisitics of forward 4 bar suspensions. I would have pasted it here, except it is over 3600 words, and over 13 printed pages. So I have linked it to its own document. It is very, very lengthy, however very informative, and a good read for many beginners

Research Paper

Leaf Springs

First, the leaf spring setup. If this setup is done correctly, it will work well, and last a long time. The most common way of setting up a leaf spring setup is to break the leaf pack apart to the longest leaf and install that back on the vehicle. That is all fine and dandy; however, it is not safe. A single leaf is not designed to take the amount of torsional flex that occurs when braking and accelerating. They can easily crack or break and you will be left stranded, possibly with a destroyed rear end. The optimum way to do a leaf spring setup is to break the pack down to the longest leaf, and the shortest, or overload leaf and have them de-arched by a shop. This will allow you to get as low as a "mono-leaf" setup, only it will be much safer. The airbag can be mounted in a variety of places, such as over the axle, behind the axle, or between the leaf spring and the frame. This type of setup is generally the least expensive, and extensive, and is very user friendly. It is also an excellent setup for the novice installer. One of the downsides to leaf springs is that you are still bound by the leafs, so you will only get so much lift out of them. Contrary to some beliefs, it is possible to lay frame with a leaf spring setup if a large enough block is used between the axle and the leaf spring or a small enough tire is used on the vehicle.

Two Links

Following is the infamous two link. Two links are pretty much the cheapest and simplest link systems around, and that is just about their only advantage. A two link consists of two bars, pivoted on the frame in front of the axle, and solidly mounted to the axle. Two links have the problem of little or no axle articulation (one wheel up, and one wheel down). Think of going into a driveway at an angle, or taking a speed bump at an angle. One of the rear tires will go up first, however, a two link doesn't like that, because it wants to lift both tires at once, by design. Other bad characteristics of a two link include high pinion angle change, excessive wheel base change, and wheel travel. The longer the bars, the less severe the problem. Someone may say, "Well at ride height the pinion angle doesn't change." As illustrated below, it does change. Something else a lot of people say is "such-and-such shop installs two links all day long, and I see them at shows all the time, so they can't be wrong." That is also false. Just because a shop does it, or you see it in magazine, does not make it right. Look at the nice pictures and descriptions below. Thank you to Larry at Innovative Air Suspension for this.

	Here is a picture of a 22" long four link bar... The end in the vise represents the front pivot point (and it actually has a bushing in it) It is level, and the angle finder in reading 0...
	And now same bar... same mounting set up... dropped 15"... The bar got 44 degrees of movement. And now think of a two link design... It pivots in the front, and is mounted solidly at the axle. So no matter what... the pinion angle has just as much movement (degree change) as the bar.

If you have 44 degrees of change at 15", that is nearly three degrees per inch. You will easily have four inches of movement in daily use; two inches up, two inches down. That equates to roughly 12 degrees of pinion angle change. And that is where you drive at, and that does matter. Pinion angle differences as small as 1 degree can cause vibration and premature pinion bearing and transmission failure.

Another device needed with any two link is a locating device, normally a diagonal link, or a pan hard bar. This prevents lateral (side to side) movement of the axle. I will go into these later on.

Three Links

Three links have two common designs; a parallel style, and a wishbone style. To imagine a parallel style, pretend like you are looking from overhead above the setup. It will have two lower bars, and one upper bar, all parallel to each other. There will also be some sort of locating device. The upper bar of this parallel style should be strong, as well as its mounts, since all the energy of the suspension is transferred through it.

A wishbone style three link is just like you would imagine. The two lower bars are the same as the parallel style; however the upper bar looks like a wishbone, and connects to either the frame in two spots, and one on the axle, or two spots on the axle, and one on the frame. The joint used where the two bars of the wishbone meet needs to be heavy duty and strong. All of the energy will be transferred through this, and you don't want it breaking. A Johnny joint is a good piece of hardware to use. This will also allow for the greatest side to side (not to be confused with lateral movement) action of the rear suspension.

Four Links

A four link offers the same advantages of a three link. This type of link setup also has two common designs; the parallel style, and the triangulated style. The parallel style is similar to the three link design, only there are two upper bars, instead of one. A locating device is still needed for the four link parallel system as well. This parallel system does not need to be overbuilt, because the load is shared with two upper bars, not one.

The triangulated four link setup has all of the advantages of the wishbone three link setup, and it fits great in a lot of places. The reason it is triangulated, is if you look at it from the top, the upper, or lower bars form a triangle. The object with the triangulated bars is to angle them enough so that there is no lateral movement.

In a properly designed and installed four link and three link system, there will be very minimal pinion angle change, and very little driveshaft plunge. This is the object of the systems, to keep the rear suspension in balance and harmony. The next section below will discuss driveshaft angles, universal joints, etc.

Locating Devices

If you have any sort of parallel link system, two, three or four link, you will need a locating device. These come in many forms, such as a pan hard bar, diagonal link, Watts link and the Jacob's ladder.

I'll just run my way down the list, so we'll start with the pan hard bar. This is the most widely used, however, most improperly setup, locating device. Basically, this bar is setup so it is mounted to the frame on one side of the vehicle, then mounted on the axle on the other side of the vehicle. The pan hard bar is the most simple to use; however, it is not the best to use because it pulls the axle, because the rear end must follow the arc created by the bar's frame mounted end. On a bagged truck, it is pretty simple to setup. Set the truck at half its allowable travel, and mount the pan hard bar parallel to the ground, and make the bar as long as possible. Doing so will minimize the amount of pull effect the bar will have.

The next locator is called a diagonal link. The diagonal link is designed for racing applications only and works extremely well under those conditions. The diagonal link is installed from the lower left front of the ladder bar or 4-link to the lower right rear. The diagonal link holds the rear end in the center of the car, allows up and down movement but no side to side movement. The most common and probably the most practical method of mounting is with a clevis that attaches to the lower link, both front and rear. The diagonal link is location positive, easy to install and easy to maintain. A diagonal link used on the street will fail, it's only a matter of time. The stress caused by the cornering of a street car puts too much bind and tension on the ends of the link and either the clevis or the rod end will fail, you just don't know when.

A watts link, when properly constructed, is the only type of link that can keep an axle's range of motion from skewing out of alignment. In a perfect watts link, there are two bars of equal length stemming from both sides of the frame that connect to a center piece on the axle that rotates. Look at the picture below. The green image is the orgin of the system, the blue image is the system moved up and down four inches, and the red line represents the the path of the axle as the it moves up and down. Notice how the axle stays centered through the entire range of motion. This is a perfect watts link. Below that is also an image of a watts link installed on a 'bagged truck.

The jacobs ladder is similar to a panhard bar, however it creates a much less movement side to side than a panhard bar does, and is also much much more difficult to properly design. Using information from www.spitzracing.com again, look at the following drawing. The distance from point A to point C is 7", and the distance from point C to point B is 14". With this type of setup, it would be like having a panhard bar that is 87" long.

Driveshaft Angles and U-Joints

I've written a seperate article that goes over the basics of driveshaft angles and the types of u-joints.