LEAF SPRING GLOSSARY AND DEFINITIONS

A

 

Aftermarket

Parts and components manufactured by companies other than the original vehicle manufacturer. Aftermarket leaf springs are designed to match or exceed OEM specifications while often offering better value and faster availability. Modern European aftermarket manufacturers maintain the same quality standards as OEM suppliers.

 

Air spring (Air suspension)

An inflatable rubber bellows used as a helper spring or complete suspension element. Air springs can be adjusted to different pressures to accommodate varying loads, providing progressive spring rates and improved comfort. Also known as air bags or pneumatic springs.

 

Arching (Camber)

The upward curvature of a leaf spring when viewed from the side. The arch provides the spring with load-bearing capacity and determines the initial ride height. As the spring is loaded, the arch flattens.

Article number (Part number)

A unique identifier assigned by the manufacturer to a specific leaf spring or component. Article numbers are essential for accurate replacement part ordering and can often be found stamped on the spring or printed on labels.

 

Auflastung

See Load upgrade (Auflastung)

 

Auxiliary spring

See Helper spring

 

Axle

The shaft or beam that connects the wheels on opposite sides of a vehicle. In leaf spring suspensions, the axle is clamped to the spring pack using U-bolts. The axle can be rigid (solid axle) or independent.

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B

 

Bump stop

A rubber or polyurethane cushion that prevents the suspension from compressing beyond its design limit. When a heavily loaded vehicle encounters a large bump, the bump stop absorbs the final compression to protect the chassis and spring from damage.

 

Bushing

See Spring bushing

 

C

Camber

See Arching (Camber)

 

CE marking

A certification mark indicating that a product complies with European Union safety, health, and environmental protection standards. All leaf springs sold in the EU must carry CE marking.

 

Center bolt (or spring center bolt)

A bolt that runs through the center of a spring pack, keeping the individual leaves aligned. Its head fits into a locating hole on the axle or spring seat to position the spring correctly.

 

CFRP (Carbon Fiber Reinforced Plastic)

An advanced composite material used in high-performance leaf springs. CFRP springs can reduce weight by up to 75% compared to steel while maintaining strength and durability. Primarily used in premium vehicles and motorsport applications.

 

Chassis

The structural frame of a vehicle that supports the body, engine, and suspension components. Leaf springs connect the axle to the chassis, transferring loads and providing suspension articulation.

 

Composite spring

A leaf spring made from fiber-reinforced plastic materials (GFRP or CFRP) instead of steel. Composite springs offer significant weight reduction, corrosion resistance, and improved ride quality, though at higher cost than traditional steel springs.

 

Conventional spring

Also referred to as a multi-leaf spring, this is the traditional leaf spring design composed of several steel leaves of decreasing length stacked together. It provides a linear or semi-progressive spring rate, depending on the leaf configuration. Conventional springs are widely used in commercial vehicles for their robustness, simplicity, and ability to carry heavy loads. They are cost-effective, easy to maintain, and can be reinforced or repaired more easily than other spring types.

 

Corrosion

The gradual deterioration of metal due to chemical reactions with the environment, typically rust on steel leaf springs. Corrosion weakens springs and can lead to cracking and failure. Regular cleaning and protective coatings help prevent corrosion.

 

D

 

Decarburization

The loss of carbon from the surface of steel due to heating in an oxygen-rich environment. Surface decarburization weakens leaf springs and can occur during improper heat treatment or amateur welding repairs.

 

Deflection

The amount a spring compresses or moves from its unloaded position when weight is applied. Measured in millimeters, deflection is a key parameter in spring design and performance evaluation.

 

E

 

Eye breakage

A failure mode where the spring eye cracks or breaks due to excessive stress, worn bushings, seized pins, or manufacturing defects. Eye breakage is one of the most common leaf spring failure points and requires immediate replacement.

 

F

 

Fatigue

Progressive structural damage that occurs when a material is subjected to repeated loading cycles. Leaf springs eventually fail due to fatigue after millions of compression and rebound cycles over their service life.

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G

 

GFRP (Glass Fiber Reinforced Plastic)

A composite material using glass fibers embedded in a plastic matrix. GFRP leaf springs offer 40-50% weight reduction compared to steel and are increasingly common in modern commercial vehicles, particularly in Europe.

 

GVWR (Gross Vehicle Weight Rating)

The maximum total weight a vehicle is legally allowed to carry, including the vehicle itself, passengers, cargo, and fuel. GVWR is specified by the manufacturer and appears on the vehicle registration documents.

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H

 

Heat treatment

A controlled heating and cooling process used to achieve optimal hardness, strength, and flexibility in spring steel. Proper heat treatment includes austenitizing (heating to 850-950°C), quenching in oil, and tempering at 400-500°C.

 

Helper spring

An additional spring element added to the main suspension system to provide extra load support. It may be a rubber, steel, or air spring that only engages when the vehicle is under heavy load, offering progressive spring characteristics.

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I

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Interleaf friction

Friction between adjacent leaves in a multi-leaf spring pack. While some friction provides damping, excessive interleaf friction can cause squeaking noises and reduce spring performance. Plastic or rubber interleaf pads reduce friction.

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L

 

Leaf spring

A structural suspension component made of one or more curved steel strips (spring leaves) that absorb shocks and support the weight of the vehicle. Leaf springs are commonly used on the rear axle of pickups, vans, motorhomes, trucks, and trailers due to their high load-carrying capacity and simple design.

 

Lifting blocks (Lifting kit)

Spacer blocks installed between the axle and leaf spring to raise the rear of the vehicle. While they increase ride height, lifting blocks do not strengthen the suspension and should not be used alone to address overloading issues.

 

Linear spring rate

A spring characteristic where the spring rate remains constant throughout its compression. This means that for every additional unit of weight, the spring compresses the same amount. Multi-leaf spring packs with equal-thickness leaves often exhibit a linear rate.

 

Load capacity

The maximum load a spring or suspension system is designed to carry safely without failure or excessive deflection.

 

Load deflection curve

A graph that shows how a spring behaves under load. It plots the vertical deflection (compression) of a spring against the amount of weight or force applied. This curve helps engineers evaluate spring performance.

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Load upgrade (Auflastung)

A German term for officially increasing a vehicle's maximum allowable weight (gross vehicle weight rating, GVWR). This requires technical modifications and certification, often involving suspension upgrades.

 

M

 

Microcracks

Tiny surface cracks that can form on leaf springs due to manufacturing imperfections, impact damage, or stress concentration. Microcracks propagate over time and eventually lead to complete spring failure if not detected early.

 

Mono-leaf spring

A single-piece leaf spring, typically parabolic in design. Mono-leaf springs offer reduced weight and improved ride comfort compared to multi-leaf packs but require careful engineering to achieve adequate load capacity.

 

Motorhome conversion

The process of converting a commercial van (typically Fiat Ducato, Mercedes Sprinter, or Ford Transit) into a recreational vehicle for camping and travel. Conversions add significant weight, often requiring suspension reinforcement.

 

Multi-leaf spring

See Conventional spring

 

O

 

OEM (Original Equipment Manufacturer)

The company that originally manufactured the vehicle or supplied parts to the vehicle manufacturer. OEM leaf springs are the original parts fitted at the factory, while aftermarket springs are produced by independent manufacturers.

 

Overloading

Operating a vehicle above its rated GVWR or axle load limits. Overloading accelerates spring fatigue, reduces safety, and is illegal in most jurisdictions. Fines can range from €1000 to €3000 in Europe.

 

P

 

Parabolic spring

A type of leaf spring made from one or two tapered leaves (thicker in the center, thinner at the ends), offering a smoother ride with reduced interleaf friction. It provides progressive spring characteristics without the need for multiple leaves.

 

Payload

The weight of cargo, passengers, and equipment that a vehicle can legally carry. Payload equals GVWR minus the vehicle's curb weight. Exceeding payload limits causes suspension damage and safety issues.

 

Progressive spring rate

A variable spring characteristic where the spring gets stiffer as it compresses. This allows for a softer ride when unloaded and greater support under heavier loads. Progressive rates can be achieved through parabolic leaves, helper springs, or staged spring designs.

 

Q

 

Quenching

A rapid cooling process in spring steel heat treatment where hot steel (850-950°C) is plunged into oil at 45-55°C. Quenching creates the martensitic structure needed for spring steel's strength and hardness.

 

R

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Reinforcement kit

A set of additional spring leaves and hardware designed to be installed below an existing leaf spring pack to increase load capacity and reduce sagging. Reinforcement kits are the most common suspension upgrade for commercial vehicles.

 

Ride height

The vertical distance between the chassis and the ground (or axle and chassis). Leaf spring enhancements can increase ride height to prevent the rear from sagging under load.

 

Rubber helper spring

A hollow rubber spring installed between the axle and chassis to provide progressive support under heavy loads. Rubber helpers are affordable, maintenance-free, and easy to install, making them popular for light to moderate overloading situations.

 

S

 

Sagging

A condition where the rear of the vehicle sits lower than intended, typically due to weakened or overloaded springs. Common in older vehicles or those frequently carrying heavy loads.

 

Shackle

A swinging link that connects the rear end of the spring to the frame of the vehicle. Shackles allow the spring to lengthen and flatten as it flexes under load, providing smooth movement.

 

Shock absorber

A hydraulic or gas-charged component that controls the rebound and compression of the suspension. Shock absorbers do not carry load but reduce vibrations and oscillations caused by road irregularities, ensuring better handling and ride comfort.

 

Shot peening

A surface treatment process where small steel or ceramic beads are blasted at high velocity onto the spring surface. Shot peening creates beneficial compressive stresses in the surface layer, dramatically improving fatigue resistance and spring life.

 

Spring bushing

A rubber or polyurethane insert inside the spring eye or shackle that reduces friction and noise while allowing controlled movement between metal parts.

 

Spring eye

The round or oval-shaped end of a leaf spring that connects to the vehicle's frame or shackle using a bolt. Most leaf springs have a front and rear spring eye, sometimes with bushings inside.

 

Spring eye bolt

The bolt that passes through the spring eye and bushing to attach the spring to the frame or shackle. Spring eye bolts must be properly torqued and are often difficult to remove due to corrosion.

 

Spring hanger (or hanger bracket)

A mounting bracket attached to the vehicle chassis where the spring eye or shackle is bolted. It helps position and secure the spring under the vehicle.

 

Spring leaf

An individual steel strip within a leaf spring. Multiple spring leaves can be stacked together to form a spring pack, with each leaf contributing to the overall strength and flexibility of the spring.

 

Spring liner

A plastic or composite sheet inserted between spring leaves to reduce interleaf friction, noise, and corrosion. Spring liners also help prevent moisture accumulation between leaves.

 

Spring pack

Also known as a leaf spring assembly, it consists of multiple spring leaves clamped or banded together. The spring pack determines the total stiffness and load capacity of the suspension system. Some vehicles use single-leaf (parabolic) springs, while others use multi-leaf packs.

 

Spring rate

The amount of force required to compress a spring by a specific distance, usually measured in N/mm. A higher spring rate means a stiffer spring. The spring rate directly influences how much a vehicle sags under load.

 

Stabilizer bar

Also known as an anti-roll bar, it connects the left and right sides of the suspension to reduce body roll during cornering. Stabilizer bars are commonly found in front and/or rear suspensions and work alongside leaf springs to improve vehicle stability.

 

Suspension system

A complete assembly of components designed to support the vehicle's weight, absorb road shocks, and maintain tire contact with the road. It typically includes leaf springs or coil springs, shock absorbers, stabilizer bars, and mounting hardware.

 

T

 

Tail lift

A hydraulic platform mounted at the rear of a commercial vehicle for loading and unloading cargo. Tail lifts add significant weight to the rear axle, often requiring suspension reinforcement.

 

Tempering

The final step in spring steel heat treatment where quenched steel is reheated to 400-500°C and slowly cooled. Tempering reduces brittleness while maintaining strength, creating the optimal balance of properties for leaf springs.

 

Tier 1 supplier

A manufacturer that supplies components directly to vehicle manufacturers (OEMs) for assembly into new vehicles. Tier 1 suppliers must meet strict quality standards and typically also serve the aftermarket.

 

Trapezoid spring

Another name for conventional multi-leaf springs, referring to their trapezoidal shape when viewed from above (wider at the center, narrower at the ends due to decreasing leaf lengths).

 

TÜV (Technischer Überwachungsverein)

German technical inspection associations that certify vehicles, components, and modifications for safety and compliance. TÜV approval is often required for suspension modifications and vehicle load upgrades in Germany and other European countries.

 

U

 

U-bolt

A U-shaped fastener used to clamp the spring pack to the axle. U-bolts must be tightened evenly to ensure safe load transfer and should generally be replaced when the spring is replaced.

 

V

 

VIN (Vehicle Identification Number)

A unique 17-character code that identifies a specific vehicle, containing information about the manufacturer, model, production year, and assembly plant. The VIN is essential for identifying the correct leaf spring variant for replacement.

 

Z

Z-spring (Lenkerfeder)

A specialized leaf spring design where the spring eye at one or both ends is positioned differently than conventional springs, creating a Z-shaped profile when viewed from the side. Z-springs are used in specific suspension geometries on some commercial vehicles.

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Related topics

 

Continue learning - explore these related topics:

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