Suspension terminology, definitions and explanations
By Jason Rodgers
A.K.A. - Gummi Bear
I’m doing the section on suspension terminology with a very simple explanation of each of them. This will include suspension components, what’s in your Bronco and what could
be in your Bronco.
(also defined as Suspension Travel) – This is the distance a wheel will travel as the suspension cycles from full extension to full compression.
- A type of spring made of wound heavy-gauge steel wire used to support the weight of the vehicle. Coil springs may be conical or spiral wound, constant rate or variable rate, and wound with variable pitch spacing or variable thickness wire. Coil springs can sag with age; and sometimes break, though not often anymore. Replacement in pairs is recommended to maintain even ride height and handling characteristics from side-to-side.
These are the type of spring that we have on the front of our Bronco. There are two common styles for our Broncos offered by the major supply houses. Constant rate and variable rate (also called progressive rate). There are arguments for and against each type, finding the one that works best for you, and the type of driving that you do. They will respond and behave differently. Progressive rate springs will be soft initially, and firm up during the compression cycle. Constant rate springs remain the same throughout their compression cycle.
– A type of spring made of flat ‘leaves’. Most commonly made of spring steel, fiberglass or some other more exotic composite materials (note: the fiberglass and composite springs are typically found in racing applications). These can also be a constant or variable rate, their shape, thickness and material can determine the rate of these springs. Leaf springs are elliptical in shape, commonly supported at one end in a fixed plane, and a shackle on the other that allows the spring to move as the suspension articulates. These are the type of spring that we have in the rear of our Bronco. It is a very dependable and effective type of spring and suspension component.
(also known as a Pan Hard Bar) – A bar that is attached to the frame, or a cross member of the frame at one end, and to the axle at the other. It keeps the axle centered, and from wandering off from side to side as the suspension cycles. Where it is attached, and its angle can manipulate suspension characteristics such as bump steer, roll center, and roll steer.
– The name pretty much says it all. These are shocks, with coils surrounding them. They are highly tuneable, and extremely versatile. They can be set up to support a wide range of vehicle applications, and vehicle weights. They come in various sizes, and there are a tremendous variety of springs available to work with them. The stroke on these shocks (for our applications) can be anywhere from 8 to 16 inches. Oil height and nitrogen pressure along with stacked discs (in most popular applications) for valving are the heart and soul of the shock itself, and manipulating them can result in an infinite number of performance possibilities. Springs can be purchased in varying lengths, and can be adjusted while on the vehicle to change the ride height.
Air Shock –
These are shocks similar in function and construction to a coilover, but without the coil. They offer weight savings, which is primarily a concern of the comp buggies. Most air shocks are not able to support the weight of an EB effectively. They have risen to popularity not only due to their weight savings, but also their comparative affordability when compared to a coilover. They will support the weight of the vehicle, and are also infinitely tuneable by adjusting the oil height, nitrogen pressure and valve discs.
Radius Arm –
These are the control arms that attach the front axle to the frame. Ford chose to use a sandwiched “C” bushing in the front, across a pair of wedges either welded or cast into the axle tube. The frame end utilized a rubber bushing sandwiched between a plate fastened to the frame. The radius arm works with the pan hard bar to keep the axle centered and moving freely. Radius arms are also sometimes referred to as Torque Arms.
Wristed Radius Arm –
A radius arm, that is hinged. For us Ford guys, this hinge will be on the passenger side. It allows the arm to twist at articulation, allowing it to droop farther than a fixed arm will.
Long arm –
A longer than stock radius arm. Commonly lengthened between 8 and 12 inches. They reduce the swaybar affect of the short stock arms, also allowing the axle to move more freely, increasing articulation.
Pitman Arm –
The lever, or arm that attaches to the bottom of the steering box and actuates the drag link to initiate steering. They are available in various drop heights, and lengths.
Linked Suspensions - These are commonly supported by coil springs, coil over shocks, or air shocks. The links can be joined at either end using a rebuildable joint such as a Johnny Joint, or a RE Joint (manufacturers names) bushings, or spherical rod ends (also referred to as Heim joints). Any of these configurations can also be referred to as ‘Trailing Arm’ suspensions. Here are a few examples, very simplified configurations and definitions:
One Link –
Also referred to as a ‘grader ball’ suspension. It is usually composed of a large, triangulated link, just below the yoke of the axle, attached near the wheel ends, and converging at a single point at the frame. These are typically accompanied by a pan hard bar for centering. They can offer tremendous articulation, but if not kept in check, can be dangerously ‘over flexy’, resulting in flops. The earliest production automobiles I know of that came with this were the early Ford cars. (Interesting note: Rather than using a pan hard to center the axle, they used a joined buggy leaf configuration, attached in the center of the axle on the bottom, and a frame cross member in the center of the top leaf. (A buggy leaf looks a lot like two traditional leaf springs, joined together at the eye on each end, resulting in a spring shaped like a football)) This suspension is also used on Unimogs. Among the unique benefits of this suspension configuration, is that since the links are fixed, it is common to plate between the suspension links, creating a nice skid plate that protects the axle and driveline from trail obstacles. This is a fairly simple configuration to set up.
Three Link –
A linked suspension configuration using 3 separate links. There are several different configurations of this. Technically, our Broncos have a 3 link front. The two radius arms, plus the pan hard bar make it a three link. Another popular configuration can have a triangulated upper with parallel lowers. Often, a suspension configuration is referred to as a 3 link, even though it technically has 4. These can have a single upper, and parallel lowers, with a pan hard bar, 2 parallel lowers, with an upper on one side, and a pan hard to keep the axle centered.
Four Link -
A linked suspension configuration using 4 separate links. There are several different configurations of this also. Triangulated uppers with parallel lowers (|/\|), parallel upper (/||\), triangulated lowers, triangulated uppers and lowers (/\/\). This is one of the most complicated suspension configurations to set up. The dynamics of it are so dramatic, that entire volumes of books have been written on this style. It can be found in sprint cars, desert racers, rock crawlers, and even a few high performance production automobiles. Done right, it is probably the most effective suspension configuration available, done wrong; it can be an ill handling mess, dangerous to the operator of the vehicle, and those around him.
Five Link –
Not very common on the trails, true to its name it uses 5 links. Most commonly using parallel uppers and lowers, coupled with a pan hard to center the axle (||_||). These are found more on straight line racers (drag race vehicles), and low riders, though I have seen a handful of vehicles on the trail running this configuration. If the links are long enough, it can be effective.
More good info -
If you find this helpful, please let me know. If you have anything to add, or there is something else you might like to see added to this, again, please let me know.