A bit off-topic:
"A wheel that can be turned though nothing turns with it, is not part of the mechanism" - what about a gyroscope wheel that is a part of a stabilizing mechanism?
This comes to show, IMHO, two things: one should be extremely careful with one's intuitions and examples must not be taken too far.
How real is the research on digit ratio? (On bogus statistics-based research see, for example: http://www.economist.com/news/briefing/21588057-scientists-think-science-self-correcting-alarming-degree-it-not-trouble).
In any case, can you please explain how you plan to use digit ratio data?