Each and every one of our models and sizes has size specific tubing. What does this mean? It means that as sizes change say for the CR, each bike has it's own combination of tube diameter and wall thickness. The reason? Ride quality. Say I was 6'4' 260#'...my frame would be built with bigger diameter tubing and slightly thicker wall to give me a stiffer ride. If you built a frame for a person that was 5' 4'' tall and 130 pounds with the same tube set, it would be much too harsh of a ride and overly heavy for the size of rider.
This size specific tubing holds true through every bike we make.
If a person was able to fit on our stock 56cm, but was much heavier than average we would want to go bigger diameter and thicker wall in the tube set to make sure the frame was stiff enough.
I hope this answers your questions.