🛞 Durometer (Shore Hardness)
A measured hardness rating for tire material, quoted as a Shore number where a higher figure means a harder tire.
On-road foam tires are commonly sold in the 30s and 40s Shore; softer generally grips more but wears out faster.
What it actually does
Durometer is the measured hardness of a tyre compound, usually given on the Shore scale — a lower number is softer. It is the closest thing the hobby has to an objective compound comparison, because brand names like "soft" and "medium" mean whatever each manufacturer wants them to mean.
In practice
Softer compounds conform to the surface and grip better but wear faster and can get greasy when hot. Harder compounds last longer and suit high-grip or abrasive surfaces. Durometer is quoted most consistently on foam tyres and on crawler tyres.
Worth knowing
Durometer describes the rubber, not the tyre. Tread pattern, carcass stiffness and the insert all change the result, so two tyres of identical durometer can still behave very differently.