You cannot convert a Shore A figure into a Shore D figure from the evidence available, so the comparison has to be built on scale, test standard and application conditions instead of arithmetic.
Rule out any quote whose hardness number does not name its scale, then require the test standard behind it and compare wheels on the trade-off the sources do describe: harder wheels roll easier, softer wheels protect floors. No source in this set publishes a conversion table between Shore A, Shore D, Rockwell R and IRHD.
Reject any hardness figure that does not name its scale
A bare number on a quote tells you nothing until you know which scale produced it. Softer rubbers are measured on the Shore A scale and harder rubbers and plastics on the Shore D scale, so the same number on the two scales does not describe the same material behaviour 9 .
Ask yourself whether the figure in front of you could plausibly sit on either scale; if the supplier has not said which, you have no basis for putting it beside a competitor's number. The reason is mechanical, not clerical.
Shore A reports how far an indenter sinks into an elastomer surface under a defined force — it is an empirical indentation reading, not a stiffness, modulus or tensile-strength value 17 .
Two wheels can carry the same Shore A number and still behave differently under load, because the reading describes a small indentation rather than how the part bends or compresses in service 17 . Treat the number as a same-scale comparison tool only, and put the scale question to the supplier before you score anything.
Check that each material is quoted on the scale it belongs on
Once the scale is named, check that it is the right one for the material. Soft elastomeric compounds sit in the 75A–85A band, while harder polyurethane formulations run from 95A up to 70D 16 .
A supplier quoting nylon on Shore A, or a soft rubber on Shore D, has either mislabelled the figure or measured the wrong property, and you should challenge it before the quote is scored. Use the band as a sanity check rather than a specification.
A published caster listing at 85 Shore A is consistent with the soft-elastomer band 9 , and a supplier product page quoting 80D sits in the harder-polyurethane range 8 . Those are per-product figures, not limits — the point is only that the scale and the material class should agree.
Where they do not, ask the supplier to re-state the value on the correct scale and to say how it was obtained.
Require the test standard and scale behind every quoted number
Two suppliers can both write "95A" and still have measured different things. ASTM D2240 is the named standard test method for rubber-property durometer hardness 10 , and ISO 22878 and ISO 22882 are named caster and wheel test standards that describe what test evidence sits behind a quoted product 21 .
Caster test programmes list wheel surface hardness on Shore A/D as a key indicator 15 . Put these checks to each supplier in writing before you compare prices.
- ✓Ask which durometer scale the figure is on — Shore A or Shore D.
- ✓Ask which test standard was used, and whether it is ASTM D2240.
- ✓Ask whether the value is a typical figure or a certified result for the supplied batch.
- ✓Ask whether the hardness was measured on the finished wheel or on the raw compound.
- ✓Ask for the test report or certificate that carries the number, not just the number on the quote.
Choose between soft and hard by push force against floor protection
Hardness is where push force and floor protection pull in opposite directions. Softer wheels deform under load and absorb energy into the contact patch, which raises the force needed to keep the cart moving; harder materials carry higher loads but concentrate pressure on the floor 5 , 31 .
On smooth floors, rolling resistance scales inversely with wheel hardness 2 . The table below puts the cited rolling coefficients and hardness bands side by side so you can see what each choice costs in push force.
| Wheel material and hardness | Rolling coefficient / push force | Load and floor effect |
|---|---|---|
| Forged steel, hard smooth floors | 0.01–0.015 coefficient | Lowest push force; no floor protection or shock absorption |
| 95A polyurethane | 0.03 coefficient | Industrial sweet spot; high floor protection, 2,500 lb per wheel |
| 70A soft rubber | 0.06–0.08 coefficient | More than double the push force of 95A; deforms under load |
| 75A–85A soft elastomer | Higher rolling resistance than 95A | Excellent shock absorption and floor protection |
| 95A–70D harder polyurethane | Lower rolling resistance | Resists flat-spotting; needs smoother surfaces for traction |
Confirm the quoted hardness still holds at your operating temperature
A hardness figure is an indentation reading taken under stated conditions, so a value quoted without a temperature range does not tell you what the wheel will do in your building. Ask for the range alongside the number, and reject a quote that gives one without the other.
Some suppliers do publish both. One wheel is quoted at 80D durometer with a -45°F to 200°F range 8 , and a nylon caster is quoted at 800 lb capacity with a -40°F to 600°F range 7 .
Those are per-product figures, but they show the pairing you should expect. Where the application runs hot, the material choice itself may change: phenolic is recommended over polyurethane or rubber when oven heat exceeds 200°F 6 .
The sources in this set do not quantify how hardness shifts with temperature for any material, so treat the range as a service envelope to verify rather than a hardness correction you can calculate.
Normalise the rest of the specification before comparing price
Hardness quotes are only comparable when the wheels are otherwise equivalent. Ask every supplier to quote against the same load, wheel diameter, brake mode, mounting dimensions, tread requirement, quantity and documentation request — if one quotation includes a central lock and another a simple brake, the prices are not comparable 14 .
Custom and OEM programmes vary their lead times and minimums by specification, so fix those variables in the RFQ rather than discovering them after award 34 .
- ✓Same load rating basis and safety margin across all quotes.
- ✓Same wheel diameter and tread width.
- ✓Same brake or lock mode — central lock, total lock or simple brake.
- ✓Same mounting dimensions and hole pattern.
- ✓Same tread material and hardness scale stated on the drawing.
- ✓Same quantity basis for the quoted unit price.
- ✓Same documentation request — test reports, certificates, sample cost and tooling charges.
Where the sources disagree on load capacity by material
Load capacity bands by wheel material do not line up between the two sources in this set, so treat any single band as a first filter that eliminates materials rather than a specification you can order against 31 .
The disagreement is worth seeing in full, because it tells you which number to verify with the supplier before you commit.
| Load capacity by wheel material (5-inch wheel) | One source reports | Another source reports | What the buyer should do |
|---|---|---|---|
| Polyurethane (lb or kg) | 500–1,500 lb | 100–300 kg | Ask which basis the rating uses before comparing |
| Nylon (lb or kg) | 800–2,500 lb | Plastic 50–150 kg | Confirm the specific wheel's rating on the stated basis |
| Rubber (lb or kg) | 200–500 lb | 100–300 kg | Verify whether the figure is static or dynamic |
| Cast iron (lb or kg) | 1,000–3,000 lb | Metal above 500 kg | Ask which standard supports the rating |
| Forged steel (lb or kg) | 2,000–10,000+ lb | Metal above 500 kg | Confirm the rating covers the complete caster |
What the sources do not establish
- No source provides a numeric conversion table or formula between Shore A, Shore D, Rockwell R and IRHD, so you cannot arithmetically translate one supplier's figure into another's scale.
- No source states whether reported hardness values are instantaneous or 15-second delayed readings, so you cannot assume two labs measured the same way.
- No source states a hardness tolerance band or whether suppliers certify hardness per batch rather than quoting a typical value.
- No source quantifies how hardness changes with temperature for any material, so a service-temperature range cannot be converted into a hardness correction.
- No source gives a hardness-to-dynamic-load-rating curve for a specific wheel type.
- No source ties cost directly to hardness scale choice.
Sources · 14
- 2casterhq.comIndustry publication2026-09
- 5casterhq.comIndustry publication2026-08
- 6casterhq.comIndustry publication2026-08
- 7casterhq.comIndustry publication
- 8algood-casters.comManufacturer technical documentation2026-09
- 9grainger.comIndustry publication
- 10casterhq.comIndustry publication2026-08
- 14secure-caster.comManufacturer technical documentation2026-08
- 15shangxincaster.comManufacturer technical documentation2025-05
- 16secure-caster.comManufacturer technical documentation2026-07
- 17filamentspecs.comUnclassified source2026-07
- 21secure-caster.comManufacturer technical documentation2026-08
- 31skt1m.comUnclassified source2026-09
- 34kpminsencasters.comIndustry peer technical page2026-08
Technical references cited for verifiability — not supplier recommendations.Browse the research library.