Usually the complete wheels, including brake rotor and freewheel, are changed when “upgrading” to 18". So a “downgrade” would be the opposite.
No, please refer to the gear ratios here:
[url]Gear ratios information about different models of Strida]
I think not, please look at these pictures, posted by Tom_:
18" Marathon Racer in the background…
…btw, 18" has 36 spokes, 16" only 24…
