...but take a look at the 100C value as well.]
I wanted to take a moment and highlight this comment. A lot of the oils I see are available in the @40C viscosity, but there doesn't appear to be a correlation with the @40C and @100C values.
Just me being me, if the Yam01 is testing 15.5 @40C and 3.45 at @100C I would think the engineers considered that. Also me being me, I'm a bit heftier than most and might choose to go just slightly thicker. I can find a 18 to 19 @40C.
I was originally going to order up some synthetic Bel-Ray HVI 5W (25% increase to 19.5 @40C) but the high end is 6.66 @100C is way up from the calculated 25% increase to the 4.3 I would be looking for.
Here's the question: Wouldn't I also want to advance by the same percentage @100C?
If I increase spring rate from 0.8 to 1.1, a 25% jump, would I also want to mimic that with the fork oil viscosity?
Motul Facotry Line Very Light with 15 @40C and 3.5 @100C looks good for factory spec replacement.
Showa SS-7 with 16.6 @40C and 3.77 @100C is about 7% to 8% difference.
Motul Facotry Line Light with 18 @40C and 4 @100C seems about a 15% difference.
ELF Moto Fork Oil Syn 2.5 the same with 18 and 4.
Is my thinking correct on this?