The knob on the back has to be tight or that will make it lean. As far as the clamp that holds the seatpost. I open it about 2", put the seatpost in and grab the both sides of the clamp and squeeze it together and then tighten it. If you really have a heavy bike, something like 35# or more, I'll leave the stand down about a foot. You picked a very good stand, good luck.
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George