Originally Posted by
Ex Pres
Sorry, not quite right. cs = club sport, a tubing set originally specified by Trek for the 6xx series starting in 1983, consisting of 531c main tubes, and chromoly (not mangy moly like 531) fork blades and stays (assumed & probably 501 tubing).
Think of 531cs as a tubeset, not as a tube designation.
It rides fine. I have an '83 600.
1983 6XX has 531c main tubes and manganese alloy for stays and fork not chromoly. It can't be 501 because it is not a manganese alloy. Trek didn't start building with 531CS until 1984.