I used my roof rack for bicycles only once.  I almost ripped everything off
pulling into a gas station....the overhang.  I found that the risk was too
great and a pain always looking out for that one tree branch or low wire or
drive-through that will end up costing $$$.  It is also a real chore getting
2 bikes way up on that roof.  A rear rack is much much more convenient and
safer.
steve