Don't know if a Triumph would be differnt than a custom build, but Street Choper magazine wrote an article on knurling for custom choppers. They stated that you could borrow or rent a knurling tool or just mark the width of your riser and put a series of small dents with a punch. This would give the clamps all the more to grab on to. No one will probably need the extra grip untill that big pot hole that wants to seen you over your handle bars, then the extra grip may turn out to be quite handy.
