What Hardness of Bushings Should I Get?
If you mean automotive suspension bushings, do not choose a hardness number in isolation. Start with the vehicle and OE reference, identify the bushing position and load path, then match the material and hardness to the way the vehicle is used. A softer bushing usually gives more compliance and isolation. A harder bushing usually limits deflection and can sharpen geometry control, but it may also transmit more noise, vibration and harshness (NVH).
The right answer is therefore not “the hardest bushing available.” For most street vehicles, the safest starting point is the OE-style specification or a documented replacement designed for the same fitment and position. A higher-hardness rubber or polyurethane option can make sense for a defined performance goal, but it should be treated as a controlled change, not a universal upgrade.
This guide covers automotive suspension bushings only. The unqualified phrase “bushing hardness” also produces results about skateboard bushings and unrelated industrial parts, so those recommendations do not transfer to a control arm, subframe or sway bar bushing on a vehicle.
The Short Answer: Choose by Fitment, Position and Use
Use this order when selecting a replacement or a performance-oriented alternative:
- Confirm fitment. Record the vehicle make, model, year, market, engine or axle variant where relevant, and the OE or catalogue reference.
- Identify the position. A control arm bushing, subframe bushing and sway bar bushing do different jobs and see different load directions.
- Define the use case. Separate quiet daily driving from heavy loads, rough roads, off-road use, fast-road driving and track work.
- Choose the material family. OE-style rubber and polyurethane may use different compound designs and different hardness ranges.
- Verify the evidence. Ask what Shore scale was used, how the sample was prepared, which batch was tested and what tolerance applies.
The number on a datasheet is useful only after these questions are answered. A 70 Shore A reading from one compound and geometry is not automatically equivalent to a 70 Shore A reading from another part, and neither reading proves how a complete vehicle will ride.
What Shore Hardness Actually Measures
Shore hardness, often called durometer hardness, is an indentation measurement. A specified indenter and force are applied to the material, and the result is reported on a scale such as Shore A. ASTM D2240 describes the penetration-based method and covers multiple durometer types. Its significance section also explains why a reading depends on the indenter, applied force, elastic modulus and viscoelastic behavior. It specifically warns that there is no simple relationship between one durometer reading and a fundamental material property.
For vulcanized or thermoplastic rubber, ISO 48-4 specifies a Shore indentation hardness method. That is helpful for defining a test, but it does not turn hardness into a complete suspension specification. Record the scale and method with the result. Do not compare Shore A, Shore D and an unlabelled “duro” number as if they were interchangeable.
In practical terms, a lower reading generally indicates a more easily indented, more compliant material, while a higher reading generally indicates greater resistance to indentation. The actual bushing response also depends on compound formulation, shape, voids, bonded interfaces, sleeve design, preload, temperature and the direction of motion. Durometer is one input to a selection decision, not a substitute for a part drawing or a vehicle test.
A Practical Hardness Decision Map
The table below is a selection framework, not a universal specification chart. Exact values must come from the vehicle application, supplier design and an agreed test method.
| Situation | Direction to investigate | Main benefit sought | Main risk to check |
|---|---|---|---|
| Quiet daily driving, OE replacement | OE-style rubber or the documented replacement range | Isolation, predictable compliance and ride comfort | Wrong fitment or installation can look like a material problem |
| Daily driver with occasional fast-road use | Moderate increase in stiffness only where the application supports it | More controlled deflection without a large NVH change | A harder compound can expose road noise and mounting issues |
| Heavy load, repeated braking or steering input | Position-specific compound and geometry review | Better control of movement under the target load | A hardness change alone may not solve sleeve, void or alignment limits |
| Off-road or harsh environment | Application-specific rubber or elastomer with environmental evidence | Controlled movement and resistance to the actual environment | Temperature, contamination and installation can dominate service life |
| Track or competition use | High-stiffness design only with a complete chassis objective | Geometry control and repeatable response | Harshness, noise and reduced compliance on public roads |
Public automotive guides often show OE-style rubber in a lower Shore A region and polyurethane in higher ranges, with “street” and “track” versions separated. Treat those ranges as orientation only. They are not a replacement for an OE specification, a validated fitment or a controlled sample comparison.
Why the Bushing Position Changes the Answer
Control arm and trailing arm bushings
Control arm and trailing arm bushings manage motion between a suspension arm and the vehicle body or knuckle. They may carry braking, cornering and longitudinal loads at the same time. A very soft design can allow more compliance and isolation, but excessive movement can change alignment or steering feel under load. A very hard design can reduce that movement while transmitting more road input.
For these positions, confirm the direction of intended compliance. Some bonded rubber bushings are designed to twist through a defined arc rather than rotate freely around the sleeve. Replacing them with a part that has a different void pattern, sleeve width or installation orientation can change behavior even when the headline hardness number looks similar.
Subframe and body mounting points
Subframe and body mounts often have a strong NVH function. They separate structure-borne vibration from the passenger compartment while still locating the subframe. A harder material may feel more precise in a performance application, but it can also transmit more road texture, drivetrain vibration or impact harshness.
When the objective is a quieter vehicle or a replacement close to factory behavior, prioritize the correct geometry, bonding and fitment before considering a harder compound. For a fleet or distributor, record the complaint type and vehicle position before changing hardness across an entire programme.
Sway bar bushings
Sway bar bushings constrain the bar while allowing it to move relative to the mount. Their response is affected by bar diameter, bracket geometry, lubrication or surface condition, and the direction of movement. A harder bushing may reduce unwanted movement, but an incorrect diameter or dry installation can create noise that is incorrectly blamed on durometer.
The appropriate choice is therefore position-specific. Do not take a hardness used on a control arm and apply it to every sway bar or subframe position on the same vehicle.
Rubber, Polyurethane and the Hardness Trade-Off
Rubber and polyurethane are not interchangeable materials with a single universal scale. A rubber bushing may be designed to use controlled shear and damping, while a polyurethane part may rely more heavily on its compound hardness, shape and lubrication requirements. The design intent matters as much as the material name.
For an OE replacement, rubber is often the more direct starting point because the vehicle was calibrated around its compliance and damping behavior. For a performance application, polyurethane can be considered when the buyer accepts a different NVH balance and has a clear reason to limit deflection. The decision should still be tied to a specific location and use case.
Avoid claims such as “polyurethane is always better” or “harder lasts longer.” A harder part can move less in one load direction while creating higher stress at a bond, sleeve or mating component. A softer part can isolate vibration well but may not meet a required movement or durability target. Those outcomes require application testing, not a generic hardness slogan.
How to Separate Hardness Problems from Fitment or Installation Problems
When a replacement bushing produces noise, early wear or a changed steering feel, check the following before changing hardness:
- Part identity: Does the part match the vehicle, model year, market and OE reference?
- Position: Is it the correct front/rear, left/right or arm location?
- Geometry: Do the outer diameter, inner diameter, width, sleeve length, voids and shoulders match the design?
- Orientation: Is a bonded or voided bushing installed in the specified direction?
- Preload: Was the final tightening performed at the required ride height or assembly position?
- Lubrication and surface condition: Is the installation method correct for the material and design?
- Adjacent parts: Are the bracket, fastener, arm and mating surfaces sound?
This checklist matters because the same symptom can have different causes. A squeak may come from friction or contamination rather than excessive hardness. A change in steering response may come from a wrong sleeve width or installation angle rather than an unsuitable Shore value.
What Evidence Should a Supplier Provide?
If you are buying a sample or building an aftermarket programme, ask for evidence that is specific enough to reproduce:
- Product identity: part number, application, position and drawing revision.
- Material description: rubber, polyurethane or another elastomer, with any approved compound designation.
- Hardness result: Shore scale, test method, test date, sample location, batch number and acceptance tolerance.
- Geometry controls: critical diameters, width, sleeve dimensions, void orientation and bonded interface requirements.
- Installation instructions: preload position, lubrication, torque sequence and any special tooling.
- Change control: notification rules if the compound, mould, sleeve, supplier or process changes.
The purpose is traceability, not paperwork for its own sake. A single hardness result from an unlabelled sample is difficult to use in a receiving inspection or a warranty investigation. The result should identify what was tested and what the number is allowed to represent.
A Five-Step Buyer Workflow
Use this workflow before approving a bushing hardness or placing a repeat order:
1. Freeze the application
Write down the target market, vehicle, year, drivetrain or axle variant, OE reference, suspension position and expected annual volume. If any of these are unknown, the hardness discussion is premature.
2. Define the job of the part
Is the bushing primarily isolating vibration, locating a subframe, controlling a suspension arm, or guiding a sway bar? State the load direction and the movement that should remain compliant.
3. Set the use-case boundary
Describe normal road mileage, rough-road exposure, towing or payload, temperature, off-road use and any track work. “Performance” is not a test condition. The supplier needs a real duty description.
4. Approve a sample against evidence
Check the drawing, material family, hardness scale, batch record, dimensions, sleeve and orientation. If the sample is installed, record the vehicle configuration and the conditions used for the evaluation. Do not turn one subjective drive impression into a universal product claim.
5. Control repeat supply
Keep a retained sample or reference record, define incoming checks and require notification of material or process changes. For a distributor, connect the part number, packaging label and fitment data so a harder or softer revision cannot silently enter the same SKU.
GSW’s automotive rubber bushings collection can be used as the product-family starting point. For a narrower RFQ, review the relevant control arm bushing, subframe bushing or sway bar bushing category and send the application information with the request.
Common Questions
Is a harder bushing always better?
No. Hardness is a trade-off between compliance and resistance to movement. A harder part may help a defined geometry-control objective, but it can also increase NVH and installation sensitivity. For an OE replacement, start with the documented application rather than a higher number.
Is 70A or 80A right for my car?
The number alone cannot answer that question. First identify the material, position, vehicle and use case. Then confirm whether the supplier’s 70A or 80A result uses the same Shore scale and a comparable test method. A catalogue value without that context is not a complete specification.
Can I compare Shore A and Shore D?
Do not treat them as interchangeable. They use different durometer types and are intended for different material hardness ranges. Record the scale with every result and follow the agreed test method.
Why did the correct hardness still squeak?
Check part identity, diameter, sleeve, bracket condition, lubrication, surface finish, orientation and installation preload. Noise is not proof that the material is too hard, and changing hardness before checking installation can create a second problem.
Should a street car use track-hard bushings?
Only when the owner understands the trade-off and the complete suspension objective supports it. A track-oriented compound may reduce compliance and increase noise or impact harshness on public roads. For a daily vehicle, an OE-style or moderate, position-specific change is usually easier to validate.
What to Include in an RFQ
When you ask for a quotation or sample, include:
- target market and vehicle make, model, year and variant;
- OE or catalogue reference and suspension position;
- drawing, critical dimensions, sleeve and orientation requirements;
- rubber or polyurethane preference and the proposed Shore scale;
- target hardness range and test method, if already defined;
- sample quantity, annual volume and packaging/label requirements;
- batch traceability, inspection records and change-notification expectations;
- installation environment, use case and any warranty or return classification needs.
This information lets a supplier discuss a real application instead of guessing from “soft” or “hard.” It also gives an importer or distributor a defensible record for catalogue data, sample approval and future returns.
Final Recommendation
For most automotive bushing purchases, choose the correct fitment and position first, then stay close to the OE material and documented hardness unless you have a defined reason to change it. Use Shore A as a measured, traceable material input. Do not use it as a shortcut for vehicle-level performance, durability or safety claims.
If you need a quotation, send the vehicle/OE reference, bushing position, dimensions, intended use, preferred material, target hardness range, sample requirement, volume and quality records you need. That is enough information to turn a vague hardness question into a testable sourcing decision.
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
- D2240 Standard Test Method for Rubber Property-Durometer Hardness – Supports the definition, scope and limitations of durometer indentation hardness.
- ISO 48-4:2018, Rubber, vulcanized or thermoplastic – Supports the Shore indentation hardness method for vulcanized or thermoplastic rubber.
