I'm not sure how a person could bend the top tube by pushing the securing bar down by hand. I have a Thule rack, Double Track 990XT, and have hauled aluminum bikes on it without any damage. If a steel top tube can be bent by pushing on the retaining mechanism, then an aluminum top tube could be dented. I have a hard enough time just getting the bar snug, much less doing damage to the top tube. My Thule rack has 3/8" rubber sleeves around the retainer arms where they come in contact with the top tube. The rubber seems to offer some cushion while hold the bike snug.
Just out of curiosity, how much force do you estimate your are pushing on the retaining arms? What kind of bike do you have and what type of steel tubing is used for the top tube? Is the diameter of the top tube on the small side, or is it thin-walled double butted tubing?
I'm interested because my rack is very similar to yours, and it could be an issue I have never thought about.
Last edited by Doug64; 12-15-21 at 11:42 PM.