I believe trial's riding originates from Motorcycling where indeed the
intent is to ride some sort of obstacle course as quickly as possible
and with as few ``dab's'' as possible. Dabbing means putting your foot
down (or falling off of course.....) The person who ``cleans'' the most
sections in the least amount of time is the winner.
I believe that one would need a mountain bike for trials riding. Low
gears and the ability to hop BIG logs are definitely an asset.
I also seem to recall seeing an article in _Bicycling_ regarding setting
up your own trials course (Parking lots full of cars are fun :-)).
Vermont Ain't Flat!
..greg franks