What Are the Properties of Rubber Bush Material?
Rubber bush material is not defined by hardness alone. In an automotive bushing, the useful properties are the combination of elasticity, recovery, stiffness, damping, fatigue resistance and stability in the service environment. The finished bushing must then turn those material properties into controlled movement through its geometry, sleeves, bond and installation.
For an importer or wholesaler, the practical answer is to define the vehicle application first, set a performance window, and request evidence that can be compared from sample to production batch. A single Shore A number cannot tell you whether a bushing is the right part, will isolate vibration as intended, or will resist the actual loads and environment.
The key properties of rubber bush material
| Property | What it controls in a bushing | What a buyer should verify |
|---|---|---|
| Elasticity and recovery | Return toward the designed position after compression, shear or twist | Test method, recovery behavior and application-specific stiffness |
| Hardness and stiffness | Initial movement, load distribution and steering or suspension control | Shore method, target range, tolerance and test conditions |
| Damping and hysteresis | How vibration energy is dissipated as heat, affecting NVH | Dynamic conditions, temperature and the complete bushing design |
| Fatigue and tear resistance | Resistance to repeated deflection, edge damage and cracking | Relevant fatigue or dynamic evidence, not only a static tensile value |
| Compression set and stress relaxation | Ability to retain support after long compression | Temperature, duration, deflection and acceptance limit |
| Heat, ozone and weathering resistance | Property change and surface cracking during service or storage | Exposure conditions, strain state and retained properties |
| Fluid compatibility | Swelling, softening or embrittlement after oil, fuel or chemical contact | Actual fluid, concentration, temperature and exposure time |
These properties interact. A softer compound may improve compliance and vibration isolation but allow more movement. A harder compound may control movement more firmly but transmit more road input. Neither is automatically better; the correct target depends on the OE design, location, load path and buyer’s failure risk.
Elasticity, recovery and flexibility
Rubber is useful in a bush because it can deform and recover without a sliding bearing surface. The material may be compressed, sheared or twisted while the bonded geometry guides that movement. Elastic recovery helps the part return toward its intended position after the load changes.
Recovery is not the same as unlimited flexibility. A bushing still needs a defined stiffness curve so that it supports the suspension or chassis at small and large deflections. The rubber formulation, voids, outer shape, sleeve position and precompression all contribute to that curve.
When comparing samples, do not rely on hand feel alone. Record the part number, dimensions, sleeve position and any agreed functional check. A sample that feels soft in isolation may be correct for one position and unsuitable for another.
Hardness, stiffness and NVH damping
Durometer hardness is a useful control value, but it is not a quality ranking. ASTM D2240 describes indentation hardness as dependent on the indenter, applied force, elastic modulus and viscoelastic behavior. That is why a Shore A result must be reported with its method, location, timing and tolerance.
Hardness and stiffness are related, but they are not interchangeable. The bushing’s geometry and loading direction can change the effective radial, axial or torsional stiffness even when two compounds have similar hardness. Damping also matters: rubber can dissipate vibration energy through hysteresis, which affects noise, vibration and harshness (NVH).
The buying question should therefore be, “What stiffness and damping behavior does this position require, and how is it verified?” It should not be, “What is the hardest rubber available?”
Fatigue, tear resistance and compression set
A suspension bush experiences repeated movement rather than one isolated pull. Repeated shear, torsion and compression can initiate cracks at edges, voids or bonded interfaces. Tensile or tear data can help describe the compound, but it cannot represent every service mode. ASTM D412 covers tensile properties for vulcanized rubber and thermoplastic elastomers while making clear that tensile results alone do not describe total end-use performance.
Compression set is another useful property. ASTM D395 provides methods for measuring the deformation that remains after rubber has been held under compression. A lower compression set can be helpful where the material must retain support, but the result depends on temperature, time, deflection and specimen. It is not a universal service-life prediction for a complete bushing.
For a buyer, fatigue and compression evidence should be tied to the actual risk. Ask whether the test represents the compound, the finished part, or both. Keep the test conditions and acceptance limits with the report so that one supplier’s result is not compared with another supplier’s result under different conditions.
Heat, ozone, weathering and fluid exposure
Temperature changes can soften, harden or otherwise shift rubber behavior. Ozone can produce surface cracking in susceptible rubber when the part is exposed under strain. ASTM D1149 defines a controlled accelerated ozone method; it is useful for comparison under stated conditions, not as a promise of a fixed vehicle life.
Oil, fuel, grease, coolant, road salt and cleaning chemicals can create a different risk. ASTM D471 covers the effect of liquids on rubber under defined laboratory conditions. The useful procurement question is not simply “Is this compound chemical resistant?” Ask which liquid, at what temperature, for how long, and what change is acceptable.
Storage deserves attention too. Heat, ozone, contamination, compression in packaging and poor stock rotation can damage a part before installation. Packaging and traceability are not material properties, but they determine whether the approved material reaches the customer in the same condition as the sample.
Natural rubber, synthetic rubber or a blend?
There is no universal winner between natural-rubber-based and synthetic compounds. Natural rubber is often valued for resilience and dynamic fatigue behavior. Synthetic families can be selected when a particular combination of temperature, weathering or fluid resistance is more important. Blends, fillers and curing systems can change the behavior within the same broad material family.
The material name is therefore only the beginning of the discussion. Ask the supplier to connect the compound choice to the load direction, movement, temperature, fluid exposure, NVH target and geometry. Do not publish a simple ranking that says one rubber is always best.
Why the finished bushing matters more than the material label
An automotive bush is a system made from rubber, metal sleeves or inserts, bonding, geometry, cure and installation. A well-characterized compound can still produce a poor part if the bond is contaminated, the sleeve is misplaced, the cure is inconsistent, the catalogue fitment is wrong or the bushing is clamped at the wrong ride height.
GSW’s rubber bush product page is the appropriate starting point for an OE or wholesale discussion. Its current collection content describes compound and hardness control, metal inserts, rubber-to-metal bonding, molding, vulcanization and batch inspection. Treat those statements as current page context, then request the documents that apply to the specific part number.
The related rubber bushing material guide explains why material selection is a trade-off, while the rubber bush manufacturing guide covers the process connection between mixing, bonding, molding, curing and inspection. Neither a material label nor a general process description replaces part-specific validation.
A buyer verification workflow
1. Define the application
Send the OE number, vehicle make, model year, axle or position, installation location, expected load, climate and known fluid exposure. For a catalogue program, record the source of the fitment data and any superseded numbers.
2. Set the performance window
Specify a hardness range or stiffness target only when it is supported by OE data, an engineering requirement or an approved sample. Add the properties that match the risk: recovery, damping, compression retention, fatigue, ageing, ozone, fluid compatibility, bond or dimensional limits.
3. Request comparable evidence
Ask for the test method, specimen or finished-part scope, conditions, sample identification, target range and acceptance limit. Quality evidence without conditions is difficult to compare and easy to overinterpret.
4. Compare sample and production batch
Check dimensions, sleeve position, flash, surface defects, hardness and any agreed functional test. Keep the OE or catalogue cross-reference with the inspection record so that a correct material is not paired with an incorrect application.
5. Control changes
For recurring programs, require notification of changes to the compound, mold, adhesive, curing process, metal insert or packaging. The goal is traceability and approval before a change becomes a fitment, NVH or warranty problem.
What to include in an RFQ
Give the supplier enough information to quote and validate the correct part:
- OE number, vehicle, model year, axle and installation position;
- target market, expected annual volume and SKU range;
- drawings, approved samples or catalogue references;
- preferred material family or hardness window, if known;
- evidence required for hardness, compression, fatigue, ageing, ozone, fluids or bonding;
- packaging, labeling, traceability and change-notification requirements; and
- known return, cracking, noise or fitment concerns.
This turns “What rubber do you use?” into a measurable sourcing conversation.
Frequently asked questions
Is a harder rubber bush better?
Not by itself. Hardness changes stiffness and movement, but it does not prove fatigue life, bond strength, ageing resistance or fitment. Compare the hardness range with the part geometry, load and application evidence.
Can a material name prove service life?
No. The material family is one input. Geometry, precompression, bonding, cure, installation and environment all affect the finished bush. Use material data as part of a validation package, not as a life guarantee.
Should buyers always choose natural rubber?
No. Natural-rubber-based compounds may suit dynamic and NVH requirements, while synthetic compounds may be selected for particular temperature, weathering or fluid conditions. The right choice depends on the application and evidence.
What test evidence should a supplier provide?
Ask for evidence matched to the risk: hardness and dimensions for basic control; compression, tensile, tear or fatigue data where relevant; ageing or ozone data for environmental exposure; and fluid-compatibility data where oils, fuels, salt or chemicals are present. Review the conditions and limits, not only the headline result.
Practical sourcing decision
The best rubber bush material is the one that satisfies the application’s performance window and can be verified consistently in samples and production batches. Define the OE and service conditions first, compare the properties that affect the real failure risks, and require evidence with test conditions attached.
For a sourcing review, send your OE numbers, vehicle and position data, target market, expected volume, SKU range, material or hardness requirements and requested validation documents through GSW’s contact page.
GSW welcomes your inquiries at any time.
Our professionalism will ensure your satisfaction.
You won’t be disappointed partnering with us; the quality of our products will win your approval.
References
- ASTM D2240 Standard Test Method for Rubber Property—Durometer Hardness — Hardness method and the effect of measurement conditions.
- ASTM D395 Standard Test Methods for Rubber Property—Compression Set — Compression-set methods and retained deformation after compressive stress.
- ASTM D412 Standard Test Methods for Vulcanized Rubber and Thermoplastic Elastomers—Tension — Tensile-property testing and its scope limits.
- ASTM D1149 Standard Test Methods for Rubber Deterioration—Cracking in an Ozone Controlled Environment — Controlled ozone exposure and cracking evidence.
- ASTM D471 Standard Test Method for Rubber Property—Effect of Liquids — Defined liquid-exposure effects on rubber.
