In a French book just out by Frederic Héran, a chapter starts with the claim than more than half of the Americans can't ride a bike, while almost all the French can. No translation problem here, I promise ("Les Français savent presque tous rouler à bicyclette (contre moins de la moitié des Américains)", p.126, "Le retour de la bicyclette", F. Heran). He really means that if you put a few adult Americans on a bike, more than half of them on average will fall instantly because they didn't learn how to ride a bike.
He gives no source, and well, overall, the book is quite superficial to my taste (but it has a very good reputation on some French bike forums though, and the author is now the kind of expert you can hear on radio when the topic is about bicycles). But this particular claim sounds incredible to me. I tried to find on the Internet the figure of the proportion of Americans who can't ride a bicycle, to no avail (because it's as little as elsewhere ?).
I think that the actual figure may be that half of Americans don't own a bike, which is a totally different picture. Or possibly that because of some health conditions, many can't imagine using a bike even if they were close to to their workplace etc (ie : a poll like "Why don't you use a bike ?" "I can't") - but more than half ?!?
Could you help me find a proof that Americans can ride a bike as much as the rest of the world ? [And yes, I read a little anti-American bias in the fact he put such a fact without any source, as the beginning of a chapter in which he explains the bicycles are back in France]