square tube is less likely to bend .
and the added weight (47 pound tire ) reduces the twist of 4 inch bumper.
( counter balancing )
tire is 47, sub-frame 22,, bike rack 49, 2 bikes 53.
second bike is 34 inches from bumper... sub-frame is 50 inches.
and YES it does greatly reduce the bounce of the bike rack.
and the bounce is what will rip the bumper off of the frame.
and the tire/wheel does not make contact with the sub-floor.
and this setup has been designed by a mechanical engineer. (not me)
and was calculated (whatever they call it) by the software he uses at work.
Ed calls it a movement dampener.. and the tire/wheel is KEY to it.
as well as a spare tire mount
. Thank You for asking.