The Disappearing Downtube

There seems to be a trend in the Custom world to push the limits. One of these areas that is pushing the limits is in the design of frames. We are seeing some radical designs out there but none more interesting then the "disappearing downtube". Safe? We can argue it...many of the older designs in the motorcycle world did not have full downtubes if any at all but they also were not housing the power plants of today either. Many of today's builders are not just your average backyard mechanic...they have engineering degrees that took years to get so they must know something. I don't know if I'm ready to crank the throttle on a bumpy road or test them on week long road trip that includes 13 hours of road a day, but they sure do look cool!