What a Shore A Hardness Number Can Tell a Rubber-Track Buyer

Keep your machine moving — rubber tracks that fit, in stock and ready to ship.

Posted on September 21, 2026 by John White

Two rubber-track quotes list Shore A hardness, and one number is higher. That does not establish which track will resist wear longer. Shore hardness is an indentation result produced with a particular scale and method under defined specimen conditions. Track life depends on properties and construction relationships that the hardness number does not measure.

The number becomes useful when the scale, test method, specimen, temperature and reading time are comparable. Without that context, a difference may reflect the test setup as readily as a material difference.

Shore A describes resistance to a specified indentation

A durometer presses an indenter into the material under the method’s defined force and geometry. The indicated Shore value reflects the material’s resistance to that indentation. It is not a direct measurement of tensile strength, tear resistance, abrasion loss or elastic modulus.

The scale is part of the result. Shore A and Shore D use different indenters and forces for different material ranges. “70 Shore A” and “70 Shore D” are not the same mechanical state with different labels, and they should not be subtracted or ranked as though one common ruler produced both.

ZwickRoell’s Shore hardness overview explains the method-specific scales, indenter response and importance of specimen and timing conditions. The applicable standard and laboratory procedure control exact test details; a general webpage is not a shop instruction.

Rubber is viscoelastic, so the indication can change after the indenter contacts the surface. A result reported immediately and a result reported after a specified dwell may differ even on the same specimen. A quote that gives only “Shore A 70” leaves the reading time unknown.

Test conditions decide whether two numbers can be compared

Specimen thickness and support affect how the indentation develops. A thin rubber layer over a rigid substrate can respond differently from a sufficiently thick standard specimen because the underlying material influences the deformation. A curved tread surface can also prevent the durometer foot from seating in the same way as on a flat specimen.

Surface condition matters. Texture, mould features, wear, contamination and local reinforcement can change contact. A measurement on a tread lug and one on an inner surface need not represent equivalent material or geometry. Identify the test location rather than assigning one unexplained result to the entire track.

Temperature and conditioning time matter because rubber response changes with condition. Comparing a cold stored track with a laboratory-conditioned specimen introduces another variable. The record should state the applicable method, conditioning, specimen temperature, thickness or construction, surface, test location and elapsed reading time.

The Dichtomatik explanation of Shore A and Shore D discusses scale choice and the effects of thin or curved specimens and support. Those principles explain why an on-product check and a standard test piece should be labelled differently. They do not supply a correction that converts one automatically into the other.

For a rubber track, the reinforcing steel, embedded cords and bonded layers make the finished product more complex than a homogeneous rubber slab. A reading on the finished track may be useful for a defined comparison, but its construction and contact location must be part of the interpretation.

Variation can come from the material or the measurement

A single reading gives no view of local variation or repeatability. Several readings at defined locations can show whether the result forms a tight group or varies across the surface. The pattern still needs interpretation.

Suppose one report gives 68, 69 and 68 Shore A on a flat conditioned specimen, while another gives 72, 66 and 70 on the curved finished tread with no stated timing. The first group is more internally consistent, but the groups were produced on different test objects and conditions. Averaging each and comparing 68.3 with 69.3 would create a neat one-point difference from unlike measurements.

Variation across a finished track could reflect different compounds, local construction, surface geometry, temperature or measurement technique. It does not prove manufacturing inconsistency until the applicable sampling and test method control those alternatives. Rounding can also hide or exaggerate a small difference when instruments report at different increments.

The useful response to unlike results is to request the missing test identity, not to apply a universal tolerance. Ask whether the value came from a standard specimen or finished product, where it was measured, which Shore scale and method applied, and when the reading was taken. Comparable results can then be interpreted within their actual specification.

Hardness does not rank complete track durability

A harder indentation response can alter how a compound deforms locally, but it does not automatically mean superior wear life. Abrasion involves surface loss under particular contact conditions. Tear resistance concerns crack growth under load. Adhesion concerns the bond between materials. Flexing and fatigue depend on repeated deformation and the reinforced track structure. Shore A measures none of those outcomes directly.

A track also has a tread pattern, guide geometry, steel core, cords and bonded rubber regions. Machine fit, tension, undercarriage condition, ground, travel and turning affect how those features are loaded. Two tracks with the same Shore A result can differ in other properties; two compounds with different hardness can each be appropriate for a design whose full requirements are known.

This is why there is no defensible universal “best Shore A” for every rubber track. A higher number is not a quality grade, and a lower number is not proof of flexibility or traction in service. The product specification has to connect the hardness requirement to its compound, test method and design.

An on-product reading can still be useful for investigation. If repeated measurements at equivalent locations under controlled conditions differ materially from the applicable product requirement, the result can support a focused material or process review. It does not establish the cause, and it should not be expanded into an expected service life.

When a quote presents hardness as proof of durability, ask for the evidence connecting that test to the claimed performance: the exact test method, specimen and result first, then the separate wear, tear or product validation relevant to the claim. If only Shore A is available, the supported conclusion is simply that the represented material produced that indentation result under the stated conditions.