Originally Posted by
wrk101
I flex that definition to include anything with a steel lugged frame and DT shifting.
+1 to Thrifty Bill's quote.
IMHO pre-early 1990's would generally qualify, as it is during that time large brands such as Schwinn changed hands and Peugeot withdrew from the US market.
With regard to mountain bikes, I'd say vintage MTB's are steel framed, built prior to the advent of low cost suspension forks and threadless headsets.