Girvin MCU ID numbers vs. Shore vs. CFD vs....?

[Ode]

    My COR spring should already be on it's way to me from Scotland, but I am interested in knowing more
about the hardness rating of the MCUs, especially as it relates to the numbers originally either stamped
on the individual elastomers themselves, or appear as numbers on small, round stickers applied to the
underside of the lower spring retainer discs. Earlier posts have suggested that those numbers could be,
or actually are, Shore numbers.
    There are 3 scales that seem appropriate: "A", widely used for rubber and elastomers / "C", for foam
and medium-hard elastomers (like an MCU?) / "O", for very soft elastomers. Intuitively, the "A" range seems
to be best suited for an elastomeric spring material, since everyday experience presents familiar examples
with properties easily accepted or rejected during comparisons, plus the number range looks about right.
This "A" scale is, I think, the scale that one of our members was referring to as the one he'd compared
numbers with using a durometer to check his own MCUs back in '07 in the 40-80 range.
     Here's a chart with comparisons:


 SHORE DUROMETER CONVERSION CHART
 A      B     C     D    O   OO
__________________________________________
100   85   77   58       
  95   81   70   46       
  90   76   59   39       
  85   71   52   33       
  80   66   47   29   84   98
  75   62   42   25   79   97
  70   56   37   22   75   95
  65   51   32   19   72   94
  60   47   28   16   69   93
  55   42   24   14   65   91
  50   37   20   12   61   90
  45   32   17   10   57   88
  40   27   14     8   53   86
  35   22   12     7   48   83
  30   17     9     6   42   80
  25   12                35   76
  20     6                28   70
  15                       21   62
  10                       14   55
    5                        8   45
Source:DSM
(from THERMAL TECH EQUIPMENTCo. Inc., Kansas City, Mo.)                           

     At the low end of the Shore "A" range of about 10 is human skin. At about 100 is shopping cart tire
hardness...but there's a fly in the ointment.
     A page from a 1996 ProFlex catalog on the RetroBike site shows an image of a bunch of yellow MCUs with
the caption: "MCU Springs - available in 10 to 160 weights". I personally have 10 MCUs which range from
40 to 110 "weight", according to the numbers stamped on their ends. Clearly this indicates that the assigned
MCU hardness numbers extend beyond the limit of the "A" scale. In fact, they extend beyond any Shore scale's maximum value of "100". A "10" on the Shore "A" scale would make the spring as compliant as a baby's butt. A 160 hardness puts the spring in Formica-table-top-hardness territory, if we extrapolate out to that number. Based on this, regardless of how well the present state of your MCUs mirrors these 2 extremes, I'm going to say that the original Girvin numbering system is, at least, an internally-developed "weight" range, perhaps arbitrary, but surely not based on any Shore scale.
     I've just found out about "Compression Force Deflection" or "CFD", an engineering measurement expressed in pounds of force per inch (psi) used to spec. urethane springs, which makes this type of value more in keeping with what would be the desired method of MCU spring evaluation. Unlike a Shore measurement, which is merely relative and compares the hardness of one material to the next, CFD numbers would likely be more interesting to someone designing a shock absorbing element, since that spec. would require a given amount of force to be applied to produce a required percentage of compression or deflection, regardless of the density or hardness of the material being compressed.
     Has anyone come across any insights into this since about '07, when the last post I've found which was
related to this was possibly made.
  
Ode