Learn Automotive Suspension Systems Explained – Frames, Springs (Coil, Leaf, Air, Torsion Bars), Shock Absorbers, Stabilizer Bars, Bushings, MacPherson Struts, Independent Front Suspension (SLA, Control Arms, Ball Joints), Rear Suspension (Live Axle, Semi-Independent) and Electronically Controlled Suspensions (Adaptive, MagneRide, Electronic Leveling)

Introduction:

The suspension system on cars and light trucks has become more advanced through the years to provide better handling, safety, and ride comfort. Today, front and rear suspensions incorporate many parts and are quite complex. As a vehicle moves, the suspension and tires must react to current driving conditions. Specifically, the suspension system supports the vehicle’s weight, keeps the tires in contact with the road, controls the direction of travel, maintains correct ride height, preserves proper wheel alignment, and reduces shock forces on irregular surfaces. These functions are interdependent and critical to vehicle performance.

The suspension system is fundamental to vehicle safety, comfort, and performance. From basic springs and shocks to advanced adaptive and active systems, each design serves the same core purposes: supporting weight, maintaining tire contact, controlling direction, preserving ride height and alignment, and reducing shock forces. Understanding these components and their functions helps appreciate how vehicles maintain stability and ride quality.

Frames:

To provide a rigid foundation for the body and a solid anchorage for the suspension, a frame is essential. Two basic types are in common use. In conventional body‑over‑frame construction, the frame is the vehicle’s foundation, the body and all major parts attach to it. The frame is an independent, separate component because it is not welded to any major body shell units. Unibody construction has no separate frame. Instead, the body parts themselves supply the rigidity and strength needed to maintain structural integrity. This design significantly lowers base weight, which increases gas mileage.

Suspension System Components:

Nearly all automotive suspensions have the same basic components and operate similarly. The basic differences lie in the construction and placement of parts.

Springs:

A spring is the core of all suspension systems. Springs carry the vehicle’s weight, absorb shock forces, and maintain correct ride height. They are compressible links between the frame/body and the tires, dampening road shock and providing comfort. If a spring is worn or damaged, other suspension parts shift out of position and experience increased wear. Various spring types are used: coil, torsion bar, leaf (mono and multileaf) and air springs. Springs are mounted in rubber or nylon to reduce road shock and noise. They are classified by spring rate the amount they compress under a specific load. A force applied causes compression proportional to the force; when removed, the spring returns to original position if not overloaded. Thus, heavier vehicles need stiffer springs. Springs handle two vertical actions: jounce (compression) and rebound (extension). Jounce occurs when a wheel hits a bump and moves up; the system pulls in the top of the wheel to maintain equal distance between wheels and prevent sideways scrubbing. Rebound occurs when the wheel drops into a dip; the system moves the wheel in at both top and bottom equally, again maintaining equal distance. During compression or extension, the spring stores energy, which forces it back to normal shape. The spring oscillates between jounce and rebound until energy dissipates. A shock absorber is added to dampen and stop this motion after jounce.

Coil Springs:

Two basic coil spring designs exist: linear rate and variable rate. Linear rate springs have a consistent shape and wire diameter, wound into a cylindrical shape with even coil spacing. As load increases, the coils twist (deflect), as load decreases, they flex back. The spring rate is the load needed to deflect the spring 1 inch (25.4 mm). For linear springs, this rate is constant regardless of compression, for example, 112 kg compresses the spring 1 inch, and 340 kg compresses it 3 inches. Spring rates are normally calculated between 20% and 60% of total deflection. Variable rate springs feature combinations of wire sizes and shapes. The most common type has consistent wire diameter, cylindrical shape, and unequally spaced coils called a progressive rate coil spring. The coil spacing gives three functional ranges: inactive coils usually end coils that introduce force, transitional coils become inactive at maximum load and active coils which work throughout the entire loading range. At stationary loads, inactive coils support all weight as loads increase, transitional coils take over until they reach capacity; then active coils carry the remaining overload, allowing automatic load adjustment while maintaining vehicle height.

Another variable design uses tapered wire active coils have large diameter, inactive coils have small diameter. Later designs deviate from cylindrical shape and include truncated cone, double cone, and barrel springs. Their major advantage is that coils can nest without touching, saving space. Unlike linear springs, variable rate springs have no predictable standard rate; they have an average rate based on a predetermined deflection. However, they can handle loads up to 30% over standard rate springs in some applications.

Leaf Springs:

Though leaf springs were the first type used on automobiles, today they are generally found on light duty trucks, vans, and some passenger cars. There are three basic types: multiple‑leaf, monoleaf, and fiber composite.

Multiple Leaf Springs:

It consist of a series of flat steel leaves bundled together with clips or a center bolt. The main leaf runs the entire length; each subsequent leaf is shorter. This allows almost any number of leaves to support the vehicle’s weight and provides a progressively stiffer spring flexing easily for minor bumps but stiffening as deflection increases. More leaves, thicker leaves, and shorter leaves make a stronger spring. As the spring flexes, leaf ends slide over each other, which can cause noise and friction. These problems are reduced by zinc and plastic interleaves. The sliding friction also dampens spring motion. Multiple leaf springs have a curve, if doubled, they form an ellipse, so they are sometimes called semielliptical or quarter elliptical the vast majority are semielliptical.

Leaf springs are typically mounted at right angles to the axle, but on some Toyota trucks they angle outward toward the front. Besides absorbing shock, they serve as a mount for the drive axle. A centering pin keeps the axle properly located, if the spring is broken or misplaced, the drive axle may sit at an angle, causing handling problems. Some vehicles have a transversely mounted leaf spring with the center attached to the chassis and the outer ends to the axle housing or wheel spindles. The front eye of the main leaf attaches to a frame bracket with a bolt and bushing; the rear eye attaches via a shackle that permits foreaft movement during acceleration, deceleration, and braking.

Monoleaf Springs:

They are usually tapered plates with a thick center section tapering toward both ends. This provides a variable rate for a smooth ride and good load carrying ability. They also lack the noise and static friction of multiple leaf springs.

Fiber Composite Springs:

They are increasing in popularity. Though sometimes called plastic springs, they contain no plastic; they are made of fiberglass laminated and bonded with polyester resins. Long fiberglass strands are saturated with resin and bundled by filament winding or compression molding. They are incredibly lightweight conventional monoleaf steel springs weigh 11‑20 kg apiece, multiple leaf can weigh almost twice as much. A fiber composite leaf spring weighs only 3.6‑4.5 kg. Reducing spring weight lowers overall vehicle weight and reduces sprung mass, which lessens the spring effort and shock control needed to keep wheels in contact with the road, resulting in a smoother ride, better handling, and faster suspension response.

Air Springs:

Air springs are used in an air operated microprocessor controlled system that replaces conventional coil springs with air springs to provide a comfortable ride and automatic front/rear load leveling. This system uses four air springs, located in the same positions as coil springs. Each consists of a reinforced rubber bag pressurized with air. The bottom of each bag attaches to an inverted piston‑like mount that reduces interior volume during jounce, increasing air pressure and making the spring progressively stiffer. A vehicle with electronic air suspension can provide a street ride about one‑third softer than conventional coils while its variable rate helps absorb bumps and prevent bottoming.

Torsion Bars:

Torsion bars serve the same function as coil springs and are often described as straightened out coils. Instead of compressing, a torsion bar twists and straightens on recoil, it resists up and down movement. One end, made of heat treated alloy spring steel, attaches to the frame; the other attaches to the lower control arm. When the wheel moves, the control arm twists the bar, absorbing shocks. The bar’s natural resistance quickly restores it to original position. Torsion bars are prestressed for fatigue strength and are directional marked right or left. Because the bar connects to the lower control arm, the lower ball joint is the load carrier. A shock absorber connects between the lower control arm and frame to damp twisting motion. Many late model pickups and SUVs use torsion bars in front suspensions because they can be mounted low and out of the way of driveline components.

Shock Absorbers:

Shock absorbers dampen motion in a vehicle. If unrestrained, springs continue expanding and contracting after a blow until all energy is absorbed, leading to a rough, unstable ride and excessive wear on suspension and steering. Shock absorbers prevent this. Despite the name, they actually dampen spring movement rather than absorbing shock; in most countries they are called dampers.
Today’s conventional shock is a velocity sensitive hydraulic damping device the faster it moves, the more resistance it provides, allowing automatic adjustment to road conditions. It works on fluid displacement during both compression and extension (rebound) cycles. A typical car shock has more resistance on extension than compression, extension controls sprung weight motion, compression controls unsprung weight motion. This motion energy is converted to heat and dissipated.
Shocks can be mounted vertically or at an angle, angle mounting improves stability and dampens accelerating/braking torque. Conventional hydraulic shocks come in two styles: single tube and double tube. The vast majority of domestic shocks are double tube heavier and run hotter than single tube but easier to manufacture. The double tube has an outer tube covering the inner tube, the area between is the oil reservoir. A compression valve at the bottom of the inner tube allows oil flow between tubes, the piston moves inside the inner tube. In a single tube shock, there is a second floating piston near the bottom that moves up and down as fluid volume changes, compressing the reservoir. Fluid does not move between a reservoir and main chamber, there are no other valves besides those in the main piston. The second piston prevents oil splashing and air bubbles, because air is compressible and slips past the piston, causing poor control on bumpy roads.

Gas Charged Shock Absorbers:

On rough roads rapid fluid passage can cause foaming mixing fluid with air leading to aeration and shock skip. Engineers have developed methods to eliminate this: a spiral groove reservoir that breaks up bubbles or a gas filled cell usually nitrogen that seals air out so fluid only contacts gas. A gas charged shock operates on the same hydraulic principle but uses a dividing piston between the oil chamber and a nitrogen gas chamber pressurized to about 25 times atmospheric pressure. As the piston rod moves down, oil displacement pushes the dividing piston against the gas, compressing it. When the rod returns, gas pressure returns the dividing piston. With static oil pressure held at approximately 100‑360 psi depending on design, gas cannot escape from the oil column, so the shock operates without aeration.

Air Shock Systems:

There are two basic adjustable air shock systems: manual fill and automatic load leveling. Manual fill systems can be ordered on new vehicles or installed on almost any vehicle. One common manual type uses a high speed DC motor to transfer a signal selected from the driver’s seat. Another uses air valves mounted at the rear, air lines run between shocks and valve and a tire pump fills the shocks to achieve desired rear height.

Shock Absorber Ratio:

Most shocks are valved to offer roughly equal resistance to jounce and rebound, indicated by a numerical formula first number jounce resistance, second rebound resistance. Passenger cars normally use 50/50 shocks, drag racers use about 90/10. Small vehicles, due to light weight and soft springs require more control in both directions. Damping rates are controlled by piston size, orifice size and valve closing force. The ratio only describes percentage of total control; two shocks with the same ratio can differ greatly in capacity so correct replacement shocks are essential.

Stabilizer Bars:

Nearly all suspension systems have a sway bar (antisway bar or stabilizer) that reduces body roll. It is a metal rod running between opposite lower or upper control arms. As one wheel responds to road surface, the bar transfers similar movement to the other wheel for example, if the right wheel drops into a dip, the bar creates a downward draw on the left wheel, producing a more level ride. Sway during cornering is also reduced, depending on thickness, the bar can reduce vehicle roll by up to 15%. If both wheels go into jounce, the bar simply rotates in its bushings. If only one wheel jounces, the bar twists like a torsion bar to lift the frame and opposite side, reducing roll. The bar is typically a one piece U shaped rod connected to control arms with rubber bushings or via sway bar links. It is also mounted to the frame with rubber bushings. If too large, the bar causes wandering; if too small, it has little effect on stability. Models without sway bars use strut rods attached to the lower control arm and frame with bushings allowing limited forward backward movement. Strut rods are directly affected by braking forces and road shocks, their failure can lead to suspension system failure.

Bushings:

Bushings are used at stabilizer bars, control arms, radius arms and strut rods. They make good pivots, minimize lubrication points, allow for slight misalignments and absorb some road shock before force transfers to the frame or body. Suspension bushings are typically made of rubber elastomers that compress under force and return to original shape. They also allow movement between parts. For example, control arms are attached to the frame with rubber bushings that act as pivot points. During suspension travel, the bushings twist they attempt to untwist, providing resistance and absorbing shock. This twisting generates heat. Rough roads or bad shocks cause excessive suspension movement, more heat and shortened bushing life excessive heat hardens rubber, leading to cracking or breakage. Worn bushings can allow parts to shift, causing vibrations, alignment problems, tire wear and poor ride/handling. A clunking noise on rough surfaces often indicates a worn bushing. Noise from dry bushings can be corrected with rubber or silicone lubricant, petroleum based lubricants will deteriorate the bushing.

MacPherson Strut Suspension Components:

The MacPherson strut suspension differs dramatically from traditional independent front suspension, but similar components operate to meet suspension demands. Its most distinctive feature is combining the spring, upper suspension locator and shock absorber into a single assembly mounted vertically between the steering knuckle’s top arm and the inner fender panel. Struts have two forms: a concentric coil spring around the strut itself or a spring located between the lower control arm and frame. The latter called modified MacPherson suspension allows minor road vibrations to be absorbed through the chassis rather than fed back to the driver through the steering system.

Struts:

The core element is the strut, which looks like a conventional shock absorber but provides damping, locates the spring and fixes suspension position. None of the strut designs use a separate shock absorber. Some versions allow independent damper servicing. Struts fall into two categories: sealed and serviceable. Sealed struts have a permanently sealed top closure; there is no access to the internal cartridge so the entire unit must be replaced. Serviceable struts have a threaded body nut that retains a replaceable cartridge. The cartridge inside a serviceable strut is generally wet oil contacts and lubricates the inner wall, sealed by the body nut, O‑ring and piston rod seal. Servicing requires thorough cleaning and careful reassembly with fresh oil. Cartridge inserts were developed to simplify servicing, the insert is a factory sealed replacement that substitutes for the original cartridge and is retained with the body nut. Most OE domestic struts are serviced by complete unit replacement, but they can be replaced with aftermarket units that allow future cartridge replacement. The strut reduces space and weight by eliminating the upper control arm and ball joint the upper mount bolted to the fender panel becomes the load carrying member.

Strut Mounts:

A mount between the top of the strut and the chassis dampens vibrations and secures the strut. Mounts often include a bearing or a bushing. Most applications fall into three designs:

Spacer Bushing: 

It is used by VW, Toyota, Mazda, Mitsubishi, and early Chrysler. It has a bearing centered in the mount and a separate inner bushing. If the bushing is cracked or bearing is seized, the mount must be replaced.

Inner Plate: 

It is used by GM and Ford. It has a rubber encased inner plate between upper and lower surface plates, the plate prevents the piston rod from pushing through if the inner plate fails. The bearing at the bottom is not serviceable, if bad, the mount must be replaced.

Center Sleeve: 

It is widely used by Chrysler. It has a center sleeve molded to a rubber bushing; the strut stem passes through the sleeve. The bearing is a separate unit. Upper and lower retainers prevent the rod from pushing through. Damaged bushings require mount replacement.

Worn strut mounts can cause independent movement of the strut and tower, leading to abnormal noise, bent strut, tower damage, and poor handling. A bad mount may cause creaking or popping due to excessive strut movement. Often the mount is replaced with the strut.

Lower Suspension Components:

The lower mounting position remains the frame with the lower control arm and ball joint retained. MacPherson suspensions continue to use sway bars on single bushing control arms, strut rods or the sway bar can be fastened to the control arm for lateral stability. The lower ball joint is a friction/steering joint that stabilizes steering and retards shimmy. The exception is modified MacPherson, where the ball joint becomes the load bearer and the upper mount becomes the steering component.

Springs:

Coil springs are used on all strut suspensions. A mounting plate welded to the strut serves as the lower spring seat the upper seat is bolted to the piston rod. A bearing or rubber bushing in the upper mount allows the spring and strut to turn with wheel steering.

Independent Front Suspension:

Front suspension systems are complex with contradictory jobs: they must keep wheels rigidly positioned yet allow steering, absorb braking torque and provide good ride and stability.

Short Long Arm Suspension:

The unequal length control arm (SLA) system is common on domestic vehicles. Each wheel is independently connected to the frame via a steering knuckle, ball joints and short upper and longer lower control arms. Because the upper arm pivots in a shorter arc, the top of the wheel moves in and out slightly but tire road contact remains constant. One SLA design uses a narrow I‑shaped lower control arm held by a strut rod attached close to the steering knuckle and to the frame ahead of the wheel. Rubber bushings at the frame allow slight movement and dampen shock. Essential components include the wheel spindle assembly, control arms, ball joints, shock absorbers and springs.

Wheel Spindle:

A wheel spindle assembly consists of a wheel spindle which is connected to the wheel via bearings and a steering knuckle which is connected to control arms. In most cases they are forged as one piece.

Control Arms:

Upper and lower control arms function as locators, fixing system position relative to the vehicle. They attach to the frame with bushings that allow separate up and down wheel movement. Outer ends connect to the wheel assembly via ball joints inserted through each arm into the steering knuckle. There are two types: the wishbone (double‑pivot) arm offers greater lateral stability the single pivot (single‑bushing) arm is lighter and requires less space but needs modifications to compensate for reduced stability.

Ball Joints:

A ball joint connects the steering knuckle to the control arm, allowing pivoting during steering and up and down movement. The stud protrudes through a rubber seal that retains grease and keeps dirt out. Some ball joints require periodic lubrication, most are maintenance free with pre lubricated nylon bearings. Ball joints are either load carrying or followers. A load carrying joint supports the vehicle’s weight and is generally in the control arm that holds the spring. They can be tension loaded or compression loaded, depending on whether the load tends to pull the ball out of or push it into the socket. Follower (friction loaded) joints mount on the arm without the spring; they do not support weight and receive less stress. Depending on spring location, either the upper or lower ball joint is load carrying. In MacPherson struts, there is usually one ball joint per side and it is typically a follower. In modified strut suspensions, the ball joint is load carrying because the spring is between the frame crossmember and lower control arm. Some ball joints have wear indicators: as the joint wears, the grease fitting recedes into the housing, when the shoulder is flush with the housing, replacement is needed. A ball joint is a ball in socket joint; wear creates looseness. Load carrying joints rely on vehicle weight to keep the ball in the socket when weight is removed, the ball may feel loose. Follower joints are held by internal friction, often with a spring to keep the ball tight, they should never have play.

Four Link Front Suspension:

A four link front suspension fixes the wheel with four rod type control arms and the tie rod. The suspension strut supports vehicle weight via the load bearing link. Separating wheel attachment and suspension elements optimizes ride quality and movement and drive forces have minimal influence on steering.

Rear Suspension Systems:

There are three basic rear suspension types: live axle, semi independent and independent. Live axle systems are on RWD trucks, vans and many 4WD passenger cars. Semi independent systems are on FWD vehicles. Independent suspensions are found on both RWD and FWD vehicles and 4WD cars.

Live Axle Rear Suspension Systems:

This traditional system uses springs (leaf or coil) with a live axle where the differential, axle, wheel bearings, and brakes act as a unit.

Leaf Spring Live Axle System:

Two springs (multiple leaf or monoleaf) are mounted at right angles to the axle with shock absorbers below the rear axle housing. The front of each spring attaches to frame brackets with a bolt and bushing through the spring eyes, the bushing allows movement and isolates noise. The center of each leaf spring connects to the axle housing with U bolts. Rubber bumpers between the axle housing and frame dampen severe shocks. Rear eye pivot bushings attach to frame shackles with bolts and bushings. Disadvantages include high unsprung weight and instability because a solid axle means one wheel’s movement affects the other, causing poor traction. Under severe acceleration, axle tramp rapid up and down jumping due to torque absorption can occur, breaking mounts and shocks and causing premature bearing wear. Tramp is reduced by mounting shocks on opposing sides of the axle. Some heavy duty vehicles have two stage springs for comfortable ride with light or heavy loads.

Coil Spring Live Axle System:

Uses two coil springs at the rear with a live axle. Because coil springs cannot locate the axle, forward and lateral control arms or links are needed this is called a link type rigid axle. Springs sit between brackets on the axle housing and the body/frame, held by vehicle weight and sometimes shocks. Control arms are channeled steel with rubber bushings. Accelerating, driving, and braking torque are transmitted through three or four control arms two forward links always used with one or two lateral links. Trailing arms mount under the axle and run forward at 90° to frame brackets. Rubber bushings permit up and down movement and reduce noise and shock. Some assemblies use two lower control arms and a tracking bar, a single torque arm replaces upper control arms, rigidly mounted to the axle housing and through a rubber bushing to the transmission.

Semi Independent Suspension:

Used on many FWD models. The suspension position is fixed by an axle beam running between two trailing arms. Though there is a solid connection, the beam twists as wheel assemblies move up and down, permitting semi independent movement and acting as a stabilizer. Frequently a separate shock and spring trailing arm system is used. Each rear wheel is independently suspended by a coil spring. A coil spring and shock absorber strut assembly is common, the strut bottom mounts to the trailing arm’s rear end and the top to the reinforced inner fender. Braking torque transmits through trailing arms and struts, which also maintain fore aft and lateral wheel positioning. A tracking bar on some systems reduces sideways axle movement.

Electronically Controlled Suspensions:

All previously described systems are passive vehicle height and damping depend on fixed nonadjustable springs, shocks or struts. Weight addition lowers the vehicle, air adjustable shocks provide some flexibility but cannot vary settings during operation. Passive systems can only offer a soft, firm or compromise ride, they cannot adjust to changing road and driving conditions. Advances in sensors and computer controls have led to new systems. The simplest are level control systems with electronic height sensors that control an air compressor linked to air adjustable shocks. More advanced adaptive suspensions continuously alter shock damping and ride height. Electronic sensors provide input to a computer, which adjusts air spring and damping settings to match conditions. The most advanced are true active suspensions hydraulically rather than air controlled, using high pressure hydraulic actuators to carry vehicle weight instead of conventional or air springs. Active suspensions can be programmed to respond almost perfectly to conditions for example, raising outside actuators and lowering inside ones during cornering to make the vehicle lean into the curve. Active hydraulic systems are presently used on a limited number of high‑performance vehicles, most manufacturers are introducing adaptive systems with pneumatically actuated air springs and dampers.

Adaptive Suspensions:

Adaptive suspensions use electronic shock absorbers with variable valving and in some cases variable air spring rates to adapt ride characteristics to road conditions or driver demands. Sensors monitor vehicle height, speed, steering angle, braking force, door position, shock damping status, engine vacuum, throttle position and ignition switching. A computer analyzes input and switches to a preset mode matching conditions. Some systems are fully automatic, others allow driver selection. Adaptive systems are less costly than hydraulic active systems but cannot eliminate body roll and have a slight delay, though some can change valving in as little as 150 microseconds.

System Components:

Designs vary; some use adjustable shocks, others use air springs on each side. The air spring membrane is like a tire, a solenoid valve and filter allow adding or releasing air. Airflow is controlled by the compressor, sensors, computer module and solenoid valves, all connected by nylon tubing.

Compressor:

A positive displacement single‑piston pump powered by a 12 volt DC motor supplies air pressure. A regenerative air dryer removes moisture. The compressor is operated by an electric relay controlled by the computer module.

Sensors:

Vehicle height sensors can be rotary Hall effect sensors for accurate measurement and compensation for road variations, preventing bottoming. Advanced systems read steering angle via a photo diode and shutter in the steering column, firming the suspension during turns. They also read engine vacuum or throttle position to stiffen during acceleration, and a brake sensor to compensate for nose dive. Some use a G sensor for sudden acceleration/braking, or a yaw sensor to detect body roll during cornering.

Electronic Shock Absorbers:

Many adaptive systems use electronically controlled shocks with variable damping, controlled by the computer based on speed, steering and braking inputs. Damping is varied by changing the size of metering orifices inside the shock via a small actuating motor that rotates a control rod. Recent advancements use real time shock damping with solenoid actuated shocks rather than motor‑driven ones, allowing almost instantaneous valving changes changes in as little as 10 milliseconds are possible when bumps are encountered.

Electronic Struts:

Some systems use an electronically controlled strut with a valve selector or variable orifice that controls fluid pressure based on sensor inputs. Some variable damping systems use air/gas instead of fluid. At speeds up to 40 mph, the orifice is fully open, from 40‑60 mph it is in normal position above 60 mph or when accelerating/braking, it shifts to firm. The variable orifice, coupled with deflected disc valving, provides optimum flow control for both rebound and jounce. In comfort mode, fluid flows mainly through the large selector orifice for minimum damping in normal mode, flow is balanced in firm mode, the selector blocks the selector orifice and fluid flows entirely through the deflected disc valving. The damper control can also raise or lower vehicle height, improving aerodynamics at highway speeds as speed increases, height reduces and front end angles down, reducing wind resistance for stability and fuel economy, as speed decreases, the body returns to normal height and level.

Computer Control Module:

A microcomputer based module controls the compressor motor via relay, compressor vent solenoid, four air spring solenoids, and electronic shock actuating motors and strut valving selectors. It receives input from all sensors. The module can perform diagnostic tests, has a preprogrammed routine for fitting air springs after servicing, and controls the dash warning light. Electrical power is distributed by the main body wiring harness, each with a specific function.

Electronic Leveling Control:

Less complicated level control systems are used on many large and mid size vehicles, they do not use a computer module. Height sensors are the only type used they sense when passenger weight or cargo is added or removed. The sensors control two circuits: compressor relay coil grounds that activate the compressor, and exhaust solenoid coil grounds that vent air. To prevent false actuation during normal ride motions, the circuitry provides an 8 to 15 second delay before circuit completion. The sensor also limits compressor run time or exhaust solenoid energization to a maximum of approximately 3.5 minutes to prevent continuous operation if a solenoid malfunctions; turning ignition off and on resets the timer. The height sensor mounts to the frame crossmember in the rear, its actuator arm attaches to the rear upper control arm via a link. The link should be attached to the metal arm when adjusting trim. When the air line attaches to shock fittings or the compressor dryer fitting, a retainer clip snaps into a groove; to remove, spread the clip, release it from the groove and pull on the line.

Adjustable Pneumatic Suspension:

Some AWD vehicles feature adjustable pneumatic suspension at front and rear, with four ride‑height positions selectable manually or automatically, providing a total range of over 20 mm of ground clearance. At highway speeds, clearance is 14 mm urban mode raises it a full inch, moderate off‑road/local driving gives 19 mm, severe off road at speeds under 40 km/h gives maximum 21 mm. The vehicle adjusts height based on speed or the driver can temporarily override with a button.

MagneRide:

MagneRide is a semiactive suspension system with shocks or struts that have no electromechanical valves or small moving parts. Instead it regulates fluid flow by a variable magnetic field produced by a small electric coil mounted in the shock. The shocks are filled with magneto rheological (MR) fluid magnetically soft particles (e.g., iron) suspended in synthetic hydrocarbon oil. The action forces MR fluid through a magnetized opening. When the shock is off, the fluid is not magnetized and flows freely. When current is sent to the coil, the fluid becomes magnetized and its viscosity changes instantly, transitioning from fluid to semi solid state proportionally to the magnetic field. With little or no current, particles are randomly distributed with strong current, the magnetic field aligns particles, stiffening the fluid and resisting flow, causing heavy damping. Damping force is proportional to viscosity which is proportional to magnetic field strength. Sensors monitoring wheel position, lateral acceleration, vehicle speed, steering angle, and brake pedal angle feed the control module, which sends current to the coil. The system provides extremely quick response about 5 ms and the fluid can react 30,000 times per second.