part 1,
the contact point of the wheel will stretch omni-directionally,
but the movement is linear so it stretches along that plane,
but figure in gravity and the metal will droop omni-directionally
in other words how many times you wheel over an area, one
direction it will stretch more clear as mud?
part 2 a smooth edge formed by folding over a 1/2" or so,
is called a folder over edge or hem edge if it has a wire
inside a wired edge.
more info on wheeling can be had at
www.metalshapers.org
and www.metalmeet.com
and the metalshapers and metalshaping groups on yahoo

take care!

tt