Bicycle

Question

Shalom, In a follow up to your answer re: bicycle on shabbath, wherein you stated that a gezera of mar'ith ha'ayin applies le'esor as it looks like travelling, based on the Talmud, which gemara are you referring to, precisely? Obviously bicycles were not known in Talmudic times. Thus I assume you see the bicycle as being within the scope of the gezera. What would you say is the rule of inclusion in the gezera? I.e., what else in your view is included in this gezera? Any activity that is commonly used for travelling? What about roller blades? Skateboards? Wheelchairs (for a non-handicapped person)? Would you agree that the rule Mishna which states re: carrying someone upon a "mitta" (= a litter), "patur af al hamitta, shehamitta tefela lo" also applies to the bicycle as being tefela lo (= to the rider)? Thus, besides the problem of the gezera, is there an issue that even outside an 'erubh (and I know of no actually sufficient 'erubhin at all here in the US) there is no 'issur de'oraita? Thanks, ASH