Suspension 101
Fabtech offers a variety of products for various suspension types. To obtain a better understanding of what each suspension type is and how it functionswe have provided the following images and descriptions. These descriptions should be considered general in nature to provide an overview of suspension types to increase product application knowledge. The listed descriptions are derived from stock type suspension design. Fabtech offers product for these suspension types along with hybrid suspensions, such as 4 Link Coilover designs for increased offroad suspension performance.
Front Suspension
Front: 4 Link Solid Axle
The 4 Link Solid Axle design also incorporates a solid drive axle and coil springs, but uses two parallel links per side, instead of radius arms, for front-to-rear positioning of the axle. The 4-link's arms run parallel from the axle housing, longitudinally along the frame-rails, mounting to pivot points on the frame. This design allows the axle to move in a specific axis reducing the effect on caster and pinion angles. A track bar is also used to keep the axle centered.
Front: A Arm Torsion Bar - 2WD / 4WD
Torsion bar IFS designs incorporate the same SLA configuration, except torsion bars are used in place of coil springs. A torsion bar is a round bar, made of spring steel, mounted longitudinally along the frame rails. The front of the torsion bar attaches to the pivot point of the lower control arm and the other end of the bar is secured to a frame crossmember. Ride height is set by preloading, or twisting, the torsion bars rear mount until the bar supports the weight of the vehicle. As the suspension travels up, the bar is further twisted, increasing the spring force. The ride height of the vehicle can be increased by further preloading the torsion bars, but there are limitations due to suspension travel, CV joint angles on 4 wheel drive models and alignment capabilities.
Front: A Arm Coilover - 2WD / 4WD
Coilover independent front suspension (IFS) vehicles incorporate unequal length upper and lower control arms (SLA, “Short Long Arm”) supporting the steering knuckle/spindle using ball joints. This configuration allows for large amounts of articulation while still maintaining proper suspension geometry. To maintain ride height, the coil spring is mounted on the shock absorber, using it as the coil spring mount. The lower control arm supports the load of the vehicle and the upper arm maintains the position of the steering knuckle, allowing the steering system to turn the knuckles left or right. Steering movements are achieved with tie rods positioned to reduce geometry change during suspension travel, also known as Bump Steer.
Front: A Arm Coil Spring - 2WD
Coil sprung IFS designs also incorporate the SLA configuration, but maintain ride height using a coil spring positioned between the frame and lower control arm. Both sides of the coil spring mount in formed pockets and usually incorporate rubber insolators to reduce noise. The lower control arm supports the load of the vehicle while the upper arm maintains the position of the steering knuckle. This allows the steering system to turn the knuckles left or right. Steering is achieved with tie rods positioned to reduce geometry change during suspension travel, also known as Bump Steer.
Front: Leaf Spring Solid Axle
The Leaf Spring Solid Axle configuration uses a multiple leaf spring-pack, on each side of the axle housing to position the axle and to support the vehicle load. The leaf springs are mounted to a hanger bracket at one end, running longitudinally along the frame-rails, with a pivoting shackle at the opposite end. This simple design locates the axle on a specific axis and supports the weight of the vehicle. A track bar is sometimes used to help center the axle on heavy duty applications.
Front: Radius Arm Solid Axle - 4WD
This design incorporates a solid drive axle using radius arms for front-to-rear positioning of the axle and coil springs to support the vehicle's weight. The front of the radius arms are attached to the axle housing and run longitudinally along the frame rails, mounting to a single pivot point on the frame. A “track bar”, mounted to the axle housing on the passenger side and the frame-rail on the driver side, keeps the axle centered side-to-side. The track bar and steering draglink geometries are matched to avoid excessive bump steer. The front axle experiences caster (the front to rear tilt of the spindle) change as the suspension cycles, which can have slight adverse effects on steering quality.
Rear Suspension
Rear: 4 Link Solid Axle
The 4 Link Solid Axle rear suspension design incorporates a solid drive axle and coil springs, with two parallel links per side for front-to-rear positioning of the axle. The 4-link's arms run parallel forward from the axle housing, longitudinally along the frame-rails, mounting to pivot points on the frame. A track bar is used on non-triangulated designs to keep the axle centered.
Rear: Leaf Spring Solid Axle
The most popular rear suspension uses a multiple leaf spring-pack, on each side of the axle housing, to position the axle and to support the vehicle load. The leaf springs are mounted to a hanger bracket at one end, running longitudinally along the frame-rails, with a pivoting shackle at the opposite end. The leaf spring design is used in heavy duty application with the addition of overload and helper leafs built into the main spring pack for additional weight capacity.
A shock absorber (damper) is a mechanical device designed to smooth out or damp sudden shock impulses and dissipate kinetic energy. In a vehicle, it reduces the ill effects of traveling over rough terrain, leading to improved ride quality and vehicle control.
Vehicles typically employ both springs (coil, leaf or torsion bar) and shock absorbers that work in conjunction with each other to provide a controlled ride. In this combination, the shock absorber is reserved for dissipating the spring's energy. Without shock absorbers, the spring would oscillate uncontrollably eventually exceeding the allowed range of suspension movement.
There are two basic types of shock absorbers used on today's vehicles, the conventional twin tube shock and the gas pressurized monotube shock.
A twin tube shock absorber consists of a thin wall inner pressure tube and outer reserve tube. The inner tube houses the valving components, piston and base valve, and is where the damping forces are generated. The outer tube acts as a reservoir for displaced fluid from the shaft volume during the compression stroke. Also contained in the outer tube is a foam sleeve or gas bag that contracts and expands with respect to shaft displacement to eliminate air pockets and increase the performance of the shock.
A monotube shock absorber consists of a single thick wall tube that houses the valving components, working piston, oil, dividing (floating) piston and nitrogen gas. Because of the single tube design, the working piston has a significantly larger surface area than a twin tube resulting in increased tunability. A monotube also dissipates heat more efficiently than a twin tube due its single tube construction being directly exposed to air flow enabling more consist control forces. The high gas pressure also improves the performance by decreasing the response time to shock impulses. The high gas pressure also prevents aeration keeping the damping more consistent across a wide variety of conditions. A monotube shock absorber requires components with significantly tighter tolerances and increased surface finishes to work effectively.