I'm not sure of the physics involved in draftign a bus, I do know the physics involved when you hit one. I was sprinting to pass when a car pulled in from a cross street and cut me off. At the same time the bus was coming to a stop and I looked up just in time to see it coming right at me. Broke the lugs at the intersection of the top head and seat tubes and just bent the rest of the frame all to custard. the front wheel of course just folded in half and the bars rotated almost 90 degrees downward in the stem, with little ribbons of metal shavings poking out. I was lucky, multiple skull fractures, broken nose, face and right arm. That was 22 years ago and I've done a lot of incredibly stupid things since then, but that one I will not repeat.