Ride Control Terms & Definitons
Active Body Control (ABC) is a type of Active Suspension developed by Mercedes-Benz in an effort to combine safe handling with ride comfort. Using high-pressure hydraulics, sensors, and microprocessors, ABC adapts automobile suspension and damping settings to different driving situations.
ABC is designed to control auto body vibrations typically caused by uneven road surfaces, braking and cornering. Mercedes-Benz claims ABC virtually eliminates body roll and pitch when accelerating, braking, or cornering. New ABC systems offered by Mercedes-Benz have different settings which can be chosen by the driver using a dashboard switch. ABC systems also permit self-leveling suspension, which raises or lowers the vehicle in response to changing load such as passengers or cargo. The first complete and ready-for-production version of ABC was introduced in 1999.
Active Suspension is a suspension system that uses a high-pressure pump, with hydraulic cylinders at each wheel, to position the wheels with respect to the vehicle. Up and down motion of the wheels is actuated by electronically controlled valves. Active Suspension systems are designed to respond to road abnormalities based on input from either the road, or driver, or both. Manufacturers offering Active Suspension systems promote the feature as providing both a comfortable and firm ride, balanced between comfort and handling.
Adaptive Air Suspension is an electronically controlled air suspension system coupled with continuously adaptive damping. Created by Audi engineers for the Audi A8, the feature also is now available for the Q7 SUV. On automobiles with Adaptive Air Suspension, each of the vehicle’s wheels have air suspension struts which are electronically controlled by a central control unit. This central unit takes its data from sensors on the axles and acceleration sensors on the body.
Audi’s innovation can make changes in milliseconds. The computer controls the damping force at each individual wheel, minimizing uncomfortable body movements when the car is braking, cornering, or off-road. Another advantage of Adaptive Air Suspension is the self-leveling feature, which makes the vehicle’s suspension height remain constant, despite the vehicle’s load. In addition, Adaptive Air Suspension allows the driver to adjust suspension characteristics, such as height and comfort settings, based on as individual driving preferences.
Adaptive Damping System (ADS) is part of the AIRMATIC suspension feature included in Mercedes-Benz S-Class vehicles. ADS adjusts each individual shock absorber depending on the vehicle’s payload, the road surface, and the driver’s selected driving style.
ADS includes a steering angle sensor, three accelerometers on the vehicle body, speed sensors on each wheel, and a brake pedal sensor. These sensors measure the lateral and longitudinal acceleration of the car when in motion. Using this data, the ADS Electronic Control Unit calculates the best damper setting for each individual wheel, and transmits the signals to actuator valves located on the shock absorbers. These valves are capable of quickly switching between different preset damping settings, as directed by the vehicle’s driver, who can select between a sporty ride or comfort mode using a dashboard switch.
An Air Suspension Compressor inflates or deflates air spring bags as necessary. When a vehicle with air suspension drops below the factory-defined height, the air suspension compressor — also simply called an air compressor or air pump — is activated and inflates the air bags or air struts.
AIRMATIC is the Mercedes-Benz name for one of its many suspension innovations, part of which stands for Adaptive Intelligent Ride control. The AIRMATIC system combines the air suspension system and Adaptive Damping System (ADS) into a single unit, including automatic self-leveling for each wheel.
AIRMATIC components include pneumatic lines, pneumatic suspension struts on all wheels, an air compressor, a central air reservoir, solenoid valves and actuators, a central electronic control unit, and various pitch and yaw sensors on the vehicle’s body. All of the components are connected via a Controller Area Network which uses numerous microprocessors to determine the suspension’s behavior based on different driving maneuvers and road surfaces.
An Air Shock is a type of overload shock absorber that can be inflated with air to increase the suspension’s load carrying ability.
An Air Spring is an air-filled rubber or elastomer bag that is pressurized to provide support to an automobile’s suspension. Air springs are used in place of conventional coil springs on some vehicles. Aftermarket air springs can be installed inside coil springs or between the axle and frame to provide additional lift support for handling overloads or towing.
Air Suspension is a type of automotive suspension that uses air springs instead of conventional steel springs. Computer-operated vents on the air springs, suspension sensors, and an onboard air compressor allow the system to maintain ride height and vary the suspension’s ride characteristics.
All Wheel Drive (AWD) features four, full-time active drive wheels to reduce wheel slippage and provide greater driver control over the vehicle. AWD is operational at all times.
GM’s Autoride is indicated by the RPO code Z55. The Autoride suspension system uses electronic shocks in the front that automatically adjusts to road conditions, becoming stiffer or softer as necessary. The rear will use an electronically controlled self leveling air shock that is monitored by ride height sensors and inflated remotely from an on-board air compressor.
Designed by Delphi, the Z55 Autoride package comes standard on the GMC Yukon Denali and Yukon XL Denali. The product is also standard on the Cadillac Escalade, Escalade EXT, and Escalade ESV where it is known as Road Sensing Suspension. GM also offers Z55 Autoride as an option for other GMT800 and GMT900 Full-Size Pickup, Sport Utility Truck (SUT) and Full-Size SUV platforms such as the Chevrolet Suburban, Tahoe, and Avalanche 1500 and an option for the GMC Yukon XL 1500.
A Bearing Plate is a component of a front strut mount. The bearing plate usually includes the steering pivot bearing along with a mounting plate.
Although traditionally called air bags or air Bellows, the correct term is air spring, although these terms are also used to describe just the rubber bellows element with its end plates.
Body Roll is the leaning or tipping of a vehicle’s body to one side when turning sharply. Body roll reduces traction and increases tire scuff because of undesirable alignment changes. Body roll primarily is controlled by a sway bar, but the stiffness of the springs and shocks also plays a part in minimizing or eliminating body roll.
A Bounce & Jounce test is a procedure used to observe how quickly or efficiently a vehicle suspension recovers after being pushed down aggressively. There is no set OE specification; however, the test can provide valuable wear indications.
Bump Stops help cushion a vehicle’s suspension, preventing the potential extensive damage that can result from bottoming out, especially when original equipment suspension has been modified.
A Bushing usually is a type of mounting insulator made of a rubber-type material. A bushing could also be a sleeve that separates components or a part used as a simple bearing.
As used in a serviceable suspension strut, a Cartridge is a shock absorber insert.
The term Chassis usually describes a vehicle’s structural frame, on which the vehicle’s body, or coach, sits. This is true for traditional “body on frame” vehicles only. In vehicles with unitized or “unibody” construction, the chassis includes everything but the doors, hood, engine, and suspension.
A Coilover Shock Absorber is one including a coil spring and an adjustable coil spring seat. The adjustment increases or decreases firmness and ride height.
A Coil Spring is a type of automotive spring made of wound, heavy-gauge steel wire used to support a vehicle’s weight. The coil spring may be located between the control arm and chassis, the axle and chassis, or around a strut.
A Coil Spring Conversion Kit replaces the use of airbags for automotive suspension. Basically, there will be coils in place of air bags. Most kits include the coil springs as well as all the parts to mount them. Airbag suspension is designed to be the softest riding suspension, and is often found on the most luxurious cars on the road. However, the ride difference between air bags and coil springs is minimal. Arnott coil spring conversion kits are easy to install and require no modifications, such as cutting or welding. In addition, coil springs have been in use for far longer than air suspension systems, they are extremely rugged, and almost never fail. In most cases, coil springs will outlast the life of the vehicle on which they are installed. In the opinion of many auto owners and auto repair professionals, an Arnott coil spring conversion kit is a great permanent solution to air suspension problems, saving money and troubleshooting headaches. The cost of a single air suspension repair is often more than a complete coil spring conversion kit.
Compressed Length is a measurement of total length when the shock or strut shaft is fully depressed into the unit’s body. The measuring points are determined by the style of mountings.
Compression Stroke also is called jounce. Compression stroke occurs when the shock or strut shaft travels into/toward the body of the unit. Compression stroke, or jounce, occurs when a vehicle with a shock or strut hits a bump in the road.
Computer Active Technology Suspension (CATS) is a Jaguar term for the company’s advanced automotive suspension system. Computer Active Technology Suspension was designed to coordinate the best possible balance between ride and handling by analyzing road conditions and making as many as 3,000 suspension setting adjustments per second via electronically controlled dampers. In newer Jaguar cars the term has been replaced with “adaptive dynamics.”
A Corner Unit Module or Assembly is a ready-to-install, or pre-assembled, combination of a suspension strut, coil spring, mount, spring insulators, and any required installation hardware.
Damper is a generic name for any automotive device — shock, strut, cartridge, or stabilizer — designed, as its primary function, to resist movement, or control movement oscillations. Sometimes referred to as dampener.
Damping, or Damping Force, is the effect, or amount, of resistance to movement.
For many countries including North American cars, the Driver’s Side is on the left, taken from the point of view of being seated inside the car, facing the front (i.e., from the driver’s seat). In this arrangement, the passenger sits to the right of the driver. For cars in about 74 countries including Australia, Britain, India, Ireland, Japan, South Africa and others, it is to drive on the left side of the road, the passenger sits on the left side, and the driver — along with all the driving controls — is on the right.
Also spelled “drier — a Dryer is an automotive device, usually a canister containing desiccant, used to remove moisture from an air suspension system, including the compressor and air bags.
Electronic Air Suspension (EAS) is the name of the air suspension system installed on the P38A, the second version of the Range Rover. The EAS provides variable height suspension for on- and off-road applications. EAS offered five suspension heights, automatically controlled based on speed and undercarriage sensors. A manual ride height switch allows the driver to control the suspension.
The EAS system includes a rubber air spring at each wheel, an air compressor, a compressed air storage tank, a valve block to route air from the storage tank to the four air springs via a series of solenoids, valves, and o-rings, an EAS computer which determines where to route air pressure, a series of air pipes which channel air throughout the system, and an air drier canister containing desiccant.
An Electronic Bypass Module (EBM) is Arnott’s exclusive Patents Pending device. The Electronic Bypass Module eliminates the triggering of dashboard air suspension warning lights. The Electronic Bypass Module is recommended for use with many of Arnott’s Coil Spring Conversion Kits, including those for the Audi allroad, large GM SUVs, GM vans, Mercedes S-Class vehicles, and the Land Rover.
Electronic Stability Control (ESC) also is referred to as Electronic Stability Program (ESP), or Dynamic Stability Control (DSC).
ESC is a computerized technology that improves the safety of a vehicle’s stability by detecting and minimizing skids. When ESC detects loss of steering control, it automatically applies the brakes to help “steer” the vehicle where the driver intends to go. Braking is automatically applied to individual wheel, such as the outer front wheel to counter oversteer or the inner rear wheel to counter understeer. Some ESC systems also reduce engine power until control is regained. ESC does not improve a vehicle’s cornering performance; rather, it helps minimize the loss of control.
Extended Length is a measurement of total length when the shock or strut shaft is fully extended. The measuring points are determined by the style of mountings.
Eye Rings consist of a metal band that houses a mounting bushing. It is a shock or strut structural component.
Front Wheel Drive is a drive system where the engine and transaxle components apply the driving force to the front wheels rather than the rear wheels.
Hydropneumatic Suspension is a type of automotive suspension system invented by Citroen. The suspension, which uses a combination of compressed oil and air, is used under license by other car manufacturers, notably Rolls Royce, Maserati, and Peugeot. It also has been used recently on some Mercedes-Benz cars. The purpose of hydropneumatic suspension is to provide a sensitive, dynamic, and high-capacity suspension system offering superior ride quality.
Independent Suspension is a suspension system allowing each wheel on a vehicle to move up and down independently of the other wheels.
The Mini-Strut is sometimes called a Spring Seat Shock. The mini-strut is a shock absorber that includes a mounting area for a coil spring. Unlike a MacPherson suspension strut, this component does not eliminate an upper control arm.
The Monotube is a damping unit design that uses a single cylinder and incorporates a separated high-pressure gas chamber. In this design, the gas does not mix with the hydraulic fluid. The gas area acts as the fluid expansion area and provides additional damping on demand. The fluid-only precision design valve area provides quicker responsiveness and more vehicle control when compared to a twin tube design.
The most common internal shock absorber designs are monotube and twin tube.
The biggest distinguishing feature between the two styles is that in a monotube, the piston rides directly on the inside wall of the shock body. In a twin tube, the piston rides inside a compression tube which is spaced slightly in from the wall of the shock body.
Twin tube shocks are cost-effective and provide satisfactory safety, handling, and control for most driving conditions. A monotube design offers what most drivers consider to be superior handling and performance, as well as a ‘sporty’ ride. Because of these performance characteristics, monotube shocks often are original equipment on luxury cars and SUVs, and are common aftermarket upgrades on vehicles originally equipped with the twin tube design.
Unless pricing is most important in a repair or upgrade discussion, many automotive experts and driving enthusiasts consider monotube shocks are preferable because of superior:
- Ride quality
- Ease of installation
Mounting Hardware generally is considered to include nuts, bolts, or other fasteners.
A Mounting Stud is a shaft with a threaded end. It is a mounting component.
Multi-Link Independent Suspension was developed to optimize wheel movement. A wheel unconstrained by attachment to an axle can move vertically, horizontally, or in a perpendicular direction. To prevent the wheel from moving in any other direction but a prescribed path, multi-link independent suspension attaches the wheel to five or six flexibly mounted links. This design can limit the wheel’s behavior to vertical movement alone.
Nose Dive occurs during vehicle braking when the front of the vehicle surges downward and the rear of the vehicle surges upward.
For most cars, the Passenger’s Side is on the right, when viewed from inside the car, seated and facing the front (i.e., from the driver’s seat). The passenger sits to the right of the driver. For many cars in countries that drive on the left side of the road, the passenger sits on the left side, and the driver — along with all the driving controls — is on the right. This concept is similar to theater terms such as Stage Right, and Stage Left.
A Pinch Bolt is a fastener (bolt) that secures, squeezes, or prevents a component from turning.
Rebound, or Rebound Stroke, is the motion of a wheel that extends the suspension. It is the opposite of jounce, or compression stroke.
Ride Control consists of four separate vehicle systems — tires, suspension, steering, and brakes — that work together to control a vehicle’s stopping, turning, handling, stability control, and ride comfort.
Ride Height is the amount of space between the base of an automobile tire and the underside of the vehicle chassis.
Sometimes called suspension-position or wheel-displacement sensors send data which is used to measure the movement of the suspension.
Road Sensing Suspension is a system designed to use various sensors to gather input about a vehicle’s body movement. The system controls the dynamics of vehicle suspension using a central Electronic Control Unit (ECU) and either hydraulic or air suspension components. Most Road Sensing Suspension systems were developed to ensure ride smoothness and reduce the effects of road surface irregularities or hazards.
In Semi-Active Suspension systems, similar to active suspension systems, the damping coefficient of the shock absorbers can be varied continuously by a control system to adapt to particular ride conditions. However, while in active suspension systems it can be necessary to supply external energy to the shock absorbers to control damping force characteristics, this is not so in semi-active suspension systems. With semi-active suspension systems, control is directed only to dissipate shock absorber energy.
Semi-active suspension systems represent an intermediate solution between passive and active suspension systems, providing better performance than the former without being as expensive as the latter.
A Serviceable Strut assembly contains a replaceable cartridge. Some designs employ an upper hex nut, while others require a special cutting tool. See the vehicle manufacturer’s manual before attempting to disassemble a serviceable strut.
A Shock, or Shock Absorber, is a device that converts motion into heat, usually by forcing oil through small internal passages in a tubular housing, to dampen automotive suspension oscillations.
Shock Fade is a condition characterized by loss of dampening action caused by fluid foaming inside a shock absorber. Rapid oscillations of a piston moving through a shock absorber churn the fluid into foam, which reduces the amount of resistance encountered by the piston. In turn, this causes the dampening action to fade, resulting in loss of control, excessive suspension travel, and reduced handling.
Shock Travel is the measurable difference between the extended and compressed lengths of a shock or strut.
Suspension Springs come in multiple forms including a coil spring, a leaf spring and an air spring. Springs are used to ensure a smooth ride.
A Spring Compressor is a tool for compressing and holding a coil spring so it can be removed or replaced, or to allow the disassembly of a MacPherson strut.
A Spring Seat is the mounting area for a suspension coil spring. The spring seat may be located on the vehicle itself or on the damping unit.
A Spring Seat Insulator is a cushion between a coil spring and spring seat. It helps reduce noise and vibration.
Spring Seat Shocks sometimes are called mini-struts. Spring seat shocks are shock absorbers that include a mounting area for a coil spring. Unlike a MacPherson suspension strut, this component does not eliminate an upper control arm.
Stability Control is a type of advanced antilock brake/traction control system that uses a vehicle’s brakes to assist steering maneuvers and to help improve vehicle handling and stability as driving conditions change. The system includes various sensors designed to monitor the driver’s steering inputs and the position of the body with respect to the road. A “yaw sensor” can tell if the vehicle is starting to understeer or oversteer in a turn. The stability control system is continuously active and will apply individual brakes to create a counter-steer effect designed to bring the vehicle back under control.
A Stabilizer Link Pin includes the bolt, stud, bushings, and washers used to attach a stabilizer (sway) bar to a suspension control arm.
Static Height Measurement is the measurement taken when a shock or strut is installed on a vehicle, on level ground. The measurement is taken from the lower measuring point to the upper measuring point.
A Steering Stabilizer is a hydraulic device similar to a shock absorber. It is attached to the steering linkage to absorb road shock and steering kickback.
A Striker Plate is an area at the top of a strut housing where the housing comes into contact with the travel-limiting bumper.
A suspension Strut Assembly is an assembly that combines the primary function of a shock absorber (as a damper), with the spring. The strut assembly includes all components in a single, fully-assembled, complete unit for quick installation.
A Strut Boot is a flexible protective boot designed to keep dirt and debris away from the polished upper shaft and upper shaft seal.
A Strut Mount is a mounting insulator between the vehicle and the strut. Front strut mounts often include a steering pivot bearing or bearing plate.
A Strut Tower includes the panels or structural members in a unibody to which the upper strut mounts are bolted.
Suspension is the term given to a combination of a vehicle’s springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose: contributing to the vehicle’s handling and braking for safety and driving pleasure.
A Sway Bar is a component often used in a suspension system to control body roll. A sway bar may be used on the front and/or rear suspension to help keep the body flat during cornering and maneuvering.
A Trailing Arm is a suspension element consisting of a longitudinal member that pivots from the body at its forward end and has a wheel hub rigidly attached to its trailing end.
A Travel Limiting Bumper is a protective insulator designed to avoid vehicle damage when the suspension bottoms out. It may be a separate part or a part of the strut boot, but it usually is a polyfoam bushing on a strut shaft or a rubber-like cushion mounted on the vehicle frame above a front or rear axle.
A Torsion Bar is a steel bar that is twisted to support the weight of the vehicle. Torsion bars are used in place of coil or leaf springs on some vehicles, and allow ride height to be adjusted to compensate for sag that occurs over time.
A Twin I-Beam is a type of independent front suspension used on Ford pickup trucks with two parallel I-beam axles, one for each wheel.
A Twin-Tube is a damping unit design with two concentric tubes: an inner working cylinder and an outer fluid reservoir. The inner, or working cylinder, is where the piston and shaft move up and down. The outer cylinder serves as a reservoir for the hydraulic fluid. There are fluid valves in the piston and in the stationary base valve. The base valve controls fluid flow between both cylinders and provides some of the damping force. The valves in the piston control most of the damping.
VIN is an acronym standing for a vehicle’s unique Vehicle Identification Number. VIN is a vehicle manufacturer’s code identifying the vehicle’ specific systems and parts. When ordering parts it is always a good idea to have the vehicle’s VIN available. Modern-day Vehicle Identification Number systems are based on two related standards that can identify the vehicle’s manufacturer (first 3 digits), general characteristics of the vehicle (digits 4-9) and provide a clear identification of a particular vehicle (digits 10-17) including model year and plant code.
Wheel Balance means the even distribution of weight around a wheel so that it rotates without vibrating or shaking. It is achieved by positioning weights on the rim to offset heavy spots on the wheel and tire assembly.