I have a paulchen w/ 1st class mounts. I also have a mountain bike, this
one with a  metal matrix frame, similar to aluminum and about the same
o.d.  I didn't even try the clamp that the paulchen came with.  I use a
few velcro tiedowns, they've work great so far, I've had it about a year
or so.  The velcro straps I have are from Panduit, they make cable ties
and things like that.

dave
www.251.org