The bushings in question are rated at 80 & 90 Shore A depending on the position of the arm per application. Softness is not an issue as these bushings, though neither is NVH (noise vibration and harshness) as these retain near-stock NVH levels. Just to provide another point of reference; Delrin is roughly 83 Shore D which is significantly stiffer than a hard hat (75D).

Just to provide a point of reference, the Mazdaspeed bushings are 70 A shore. Assuming a 10-20S difference, the SuperPros are actually quite a bit stiffer then the MS bushings.

Durometer Scale Tutorial

There are several scales of durometer, used for materials with different properties. The two most common scales, using slightly different measurement systems, are the A and D scales. The A scale is for softer plastics, while the D scale is for harder ones. However, the ASTM D2240-00 testing standard calls for a total of 12 scales, depending on the intended use; types A, B, C, D, DO, E, M, O, OO, OOO, OOO-S, and R. Each scale results in a value between 0 and 100, with higher values indicating a harder material.[2]


Method of measurement

Durometer, like many other hardness tests, measures the depth of an indentation in the material created by a given force on a standardized presser foot. This depth is dependent on the hardness of the material, its viscoelastic properties, the shape of the presser foot, and the duration of the test. Short durometer allows for a measurement of the initial indentation, or the indentation after a given period of time. The basic test requires applying the force in a consistent manner, without shock, for 15 seconds, and measuring the depth of the indentation. If instantaneous depth is desired, force is applied for only 1 second. The material under test should be approximately 6.4 mm (.25 inch) thick.[3]

Testing equipment - Shore Durometer Type A and D[3] Durometer Indenting foot Applied force (g) Type A Hardened steel rod 1.1 mm - 1.4 mm dia, with a truncated 35º cone, 0.79 mm dia. 822 grams Type D Hardened steel rod 1.1 mm - 1.4 mm dia, with a 30º conical point, 0.1 mm radius tip 4550 grams The final value of the hardness depends on the depth of the indenter's penetration. If the indenter penetrates 2.5mm or more into the material, the durometer is 0 for that scale. If it does not penetrate at all, then the durometer is 100 for that scale. It is for this reason that multiple scales exist. Durometer is a dimensionless quantity, and there is no simple relationship between a material's durometer in one scale, and its durometer in any other scale, or by any other hardness test.[1]


Durometer of various common materials

An automotive tire tread, one of the many rubber or polymer objects categorized by its durometer hardness. Tires typically range from 50A to 70A, depending on their application.

Examples:

Material Durometer Scale
Hard Hat 75 D
Non-spark hammer 60 D
Hard skateboard wheel 100 A
Solid truck tires 50 D
Soft skateboard wheel 70 A
Automotive tire tread 70 A
Door seal 55 A
Rubber band 25 A
Sorbothane 40 OO
Sorbothane 0 A
Chewing Gum 20 OO