I carry a 22" expandable rollaboard. It doesn't work as a carry on if it is expanded. My general rule is to carry on when departing my home airport but I check that sucker on the way home! I find that two pair of shoes fit perfectly end to end in a 22". That way the soles are all facing the side of the bag and less likely to touch my clothes. I should invest in some shoes bags but alas that hasn't happened.