I propose that L(9) = 66 (inches) for the Sage GII is the single most realistic, casting-behavior-specific designation ever put on a fly rod. It IS a measure of stiffness….but related to actual casting flexion. A shortening of the “lever” to 66” is the single most important measure because up to 80% of line speed will be controlled…and “felt” by the caster…as lever of that length.
L(9) = 66 also states that, compared to 9’ rod with L(9) = 72 there will be 6 MORE INCHES OF LOADING DISTANCE in the loading phase. This rod will be shorter, and “slower” to load. More about that later.
What about the L(8) and L(10) for that rod? If I had a workable F(8) and F(10) I could fill in the blanks because I have exact full weight x deflection curves for those rods. But note, comparing the L(X) between two rods is a comparison of stiffness. Comparing a DIFFERENCE between the L(X-1) or L(X+1) between to rods with the same L(X) is a comparison of TAPER!
I have said that during the acceleration phase that taper has little or no significance. That is true so long as Force is constant….meaning that, at that force, rod behavior is unchanging. But, if additional force is applied, two rods with L(9) = 54 will NOT necessarily respond equally if they have a different taper.
But one should NOT apply more force during the acceleration phase. That is true….unless….that force is a HAUL!! Taper DOES matter in this case.
I have postponed a breakdown of the forces during the haul for reasons that will become apparent. But suffice it to say for now that the haul adds force and that will necessarily affect rod flexion and rods of different tapers will THEN respond differently.
Let me re-state the concept of taper. The important and working difference in taper between two rods is the slope (first derivative in calculus terms) of the weight x deflection curve…and again at working flexions. Stated more simply, hanging an addition 50 grains off of one rod might cause 6 more inches of delfection but on another rod might only cause 4 inches of deflection.even though their L(9) STIFFNESS is equal. The difference is an expression of taper.
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