urethane shore scales

[bucksaw87]

from Rogers Corporation: PORON Compression Force Deflection Versus Shore Hardness
does that look about right? i know chaput had a scale with A and D shore on it, but this one's more complete

[Slim]

The A scale is fine for all the soft wheel ratings because it's easy to represent the difference between a 78a wheel and a 80a wheel. The problem comes once you approach the theoretical maximum hardness (100). Some other scales have more of a range of numbers to represent the difference between, for example, a 98a wheel and the hardest possible urethane wheel (which we'd have to call 99a still). So...is it a hard 99 or a slightly softer 99? We have no way of doing that with the A scale. It'd be good to switch to the D scale then. As you'll notice in the chart above, the D scale has 12 numbers to represent the difference between the same thing that the A scale has 5 numbers. (I.e. 95 to 100A or 46 to 58D. So a 99a wheel could be a 55 or 56 or 57 or 58D).

[enemy combatant]

I've also read that in addition to providing too coarse a measurement, tools built to measure hardness across the Shore A scale also give less than optimally accurate readings for materials with a hardness greater than 95. For those materials an instrument calibrated to the D scale is recommended.

It would be helpful if specs were published regarding the resilience of wheels and bushings too as there also exist tools to give standard measurements of it.