So what is a "lightweight"? I'd say in the Classic & Vintage context, anything under 30 lbs would qualify. A touring bike, fully outfitted with fenders and racks, would probably weigh a bit more. My first lightweight, a 1953 Claud Butler New Allrounder, was 27 lbs, if I recall. It was plain gauge 531 with steel rims and crank, rear derailleur and Bluemels fenders. Fast forward, my '77 Nishiki Landau weighs 24.5 lbs with a db CrMo frame, alloy crank and rims. My '81 Nishiki Ultimate is 20.5 lbs. I'd say 20 lbs or less would be a pretty light vintage bike and between 22 and 28 about average. Of course, these weights seem quite hefty compared to today's plastic wonders which can be as little as 12 lbs (15 lbs being the minimum allowed for the Tour de France). However, there were many vintage track bikes down in that range and vintage fixed wheel bikes could easily be between 15 and 20 lbs.