Nigel wants to know what drove the US bike boom (specifically lightweights?). The obvious answer is demographics, as the baby boomers needed bikes in booming numbers. However, I will attempt to answer the question based on my own experiences growing-up middle-class in Southern California during the 60's...and that answer is...Schwinn!
Schwinn was the standard by which other brands were measured during the 50's and 60's. As many of us graduated from 20" to 24' to 26" and 27" wheel sizes, increased gear ratio capabilities ("speeds") and finally derrailleur bikes came along for the ride. Although I personally never cared much for the ubiquitous Varsity or Continental, their popularity cannot be denied along with their part in making derailleur bikes socially acceptable, even desireable! By the time I was in my late-teens during the mid-60's, the stage was set with consumers eager to buy the afffordable (the dollar was still worth something) and relatively high-quality (compared to the domestic drivel) lightweight offerings that were starting to trickle-in from the Continent. That trickle became a torrent in the early-70's and lasted until the mid to late-70's when the sinking value of the dollar made the then-improved bikes from Japan the better value.
You may have noticed something of concern in reading this that was unintended. That is, the dollar is still sinking and as developed economies price themselves out of the U.S. market, developing economies take their place! This may seem like perpetual motion except for the fact that quality (as I define it for myself) continues to ebb.
Jack Romans
Sacramento, Califa