Shore Hardness for Caster Wheel Treads: What It Decides, and What to Verify Before the RFQ

What Shore hardness actually controls

Shore hardness, also called durometer, measures how hard the wheel tread material is 15 . It is one of several parameters that influence damping, rolling resistance, load support and surface pressure.

A single number cannot be read as a performance promise 3 . The mechanism runs in one direction: a harder tread has higher compressive strength and deforms less under load.

That raises the load it can carry, but it concentrates pressure on the floor and transmits more vibration 12 , 16 . A softer tread does the opposite.

It spreads load over a larger contact area and damps vibration, which protects floors and cuts noise, at the cost of load capacity and a higher risk of flat-spotting under sustained heavy static load 1 , 2 . Because the trade-off is real, treat hardness as a lever you set against floor type, load and noise target.

Do not treat it as a value to copy from a catalogue 3 , 15 . Load capacity itself is not set by hardness alone: wheel diameter, tread width, bearing type, core material and load distribution also determine the rating 16 , 19 , 20 .

Shortlist the tread family by floor type first

Before any hardness number goes into the RFQ, decide which tread family fits each floor in the facility. Soft treads — rubber, TPR/TPE and soft polyurethane — are reported to distribute weight, protect delicate surfaces and reduce noise.

Hard narrow treads and point loading can mark or chip floors such as epoxy 2 , 9 , 14 . Rubber is reported quieter and gentler on delicate floors.

Polyurethane is non-marking and safe on concrete, epoxy and tile, but rubber wins for hospitals, offices and hardwood 1 , 4 , 17 . Nylon and other hard plastics handle heavier loads and resist chemicals, water and impact, but they are reported noisy and less floor-protective than softer materials 9 , 11 , 14 .

For a mixed facility, that means you may need more than one tread family rather than one compromise across the whole site. The sources do not quantify how many Shore points of softness produce a given reduction in floor damage or noise.

The family choice is the decision you can make from evidence; the number is a later, per-model confirmation 1 , 15 , 16 .

Rule out quotes that give hardness without a load rating

A hardness figure on its own does not tell you what the wheel will carry. Harder treads are reported to carry higher loads because their compressive strength is higher, while softer treads deform and can flat-spot under sustained heavy load 1 , 12 , 16 .

No source in this set gives a Shore value at which a specific load rating is achieved 16 , 19 , 20 . One source reports polyurethane at 2,000+ lbs per caster against rubber at 500 lbs, and rubber at 200–500 lbs per caster 1 ; another reports rubber and polyurethane together in a 100–300 kg band 8 .

Those bands are supplier-reported first filters, not specifications, and they do not line up neatly 8 , 12 . Treat any quote that offers a durometer number without a stated load basis as incomplete.

Ask which standard supports the rating and whether it covers the complete caster or only the wheel 12 .

Compare the tread families on the criteria that decide the purchase

Polyurethane is repeatedly positioned as the balance material — rubber-like elasticity with hard-material durability. That is why it appears in both floor-protection and load discussions 4 , 7 , 11 , 13 , 19 .

Rubber wins where noise and delicate floors matter most, and nylon wins where durability and heavy loads matter most, at the cost of noise and floor protection 1 , 9 , 11 , 14 . No source provides comparative prices for these three treads, so the cost column cannot be filled from this evidence.

Tread and core material is a listed cost driver in caster quoting, and testing and compliance can add engineering effort, but the price difference between rubber, polyurethane and nylon treads is not established here 10 .

Write the hardness clause as a range tied to floor type

The only concrete Shore figure in this source set is Shore A 85–92, recommended for lighter-coloured polyurethane in the most floor-sensitive environments 1 . Other sources confirm that polyurethane is offered across multiple durometer ranges.

They also confirm that harder grades support heavier loads while softer grades give better grip and shock absorption, but they give no numbers 15 , 16 . That means the range you write into the RFQ should be tied to the floor type.

Soft treads for hardwood, linoleum and other delicate surfaces, harder materials such as nylon or hard polyurethane for carpeted floors where maneuverability matters 1 , 2 , 9 . Ask the supplier to confirm the durometer of the actual wheel model you are buying, on the scale they use, rather than accepting a family-level figure.

The sources do not define the Shore A versus Shore D scales or state which scale applies to rubber, polyurethane and nylon treads. The scale itself is a question for the supplier, not an assumption you can make 1 , 15 , 16 .

Verify load testing before you accept a soft tread

A soft tread is the right answer for floor protection, but it is also the tread most prone to flat-spotting under sustained heavy static load. The load testing behind the quote matters as much as the durometer 1 , 22 .

Ask for the test evidence on the specific model, not a company capability statement.

• ✓Confirm the static load test: 150% of rated load held for 24 hours, checking for structural deformation or cracking
• ✓Confirm the dynamic load test: 100,000+ cycles at 5 km/h, checking axle and bracket fatigue
• ✓Confirm the static pressure test covers flat-spotting of the tread under prolonged heavy pressure
• ✓For rubber treads, check whether the application holds static load above 50% of rated capacity, the threshold at which flat spots are reported per ASTM D395 compression-set behaviour
• ✓Ask which standard supports the rating and whether it covers the complete caster or only the wheel

Decide how much budget to attach to tread material

Tread and core material is a listed cost driver in caster quoting, affecting rolling noise, wear, floor protection and chemical resistance. Application-specific testing or documentation can add engineering effort 10 .

Polyurethane is reported to last 3 to 5x longer than rubber and to resist chemicals and abrasion. That is the kind of difference that shifts total cost of ownership rather than unit price 1 .

But no source in this set gives comparative prices for rubber, polyurethane and nylon treads, so you cannot derive a hardness-to-price rule of thumb from this evidence 10 . Compare equivalent specifications — same load basis, same mounting, same brake — rather than the lowest unit price.

Ask the supplier to list every deviation from the RFQ so a material substitution does not quietly change the approved wheel 10 , 14 .

Where the load figures disagree, and what to do about it

The load bands for rubber and polyurethane do not line up between sources, and one source itself flags that its two tables do not match 8 , 12 . The figures are supplier-reported first filters, not specifications.

Use them to eliminate materials, then confirm the specific wheel's rating on the basis you checked 12 . A published rating is only comparable if you know what it measures — static or dynamic, wheel only or complete caster 12 .

What the sources do not establish

• No source defines the Shore A versus Shore D scales or states which scale applies to rubber, polyurethane and nylon caster treads.
• No source provides typical Shore ranges for rubber, polyurethane or nylon treads; the only Shore figure in this set is one source's recommendation of Shore A 85–92 for floor-sensitive polyurethane.
• No source names ASTM D2240 or ISO 868, or explains how either standard ensures Shore hardness consistency and comparability.
• No comparative price data for rubber versus polyurethane versus nylon treads.
• No quantitative relationship between Shore values and noise levels, floor damage or load ratings.
• No source explains how tread hardness interacts numerically with wheel diameter and width for a given load.
• Load rating bands for rubber and polyurethane are inconsistent between sources and are flagged as supplier-reported first filters, not specifications.