As a bike dealer, I have on occaision worried about the rugged factor when selling a bike to the larger folks. In 1990, a 12 year old kid, Jason, came into my shop looking for a new bike. I only mention his age because at that time he weighed in at 325. The bike held up fine, but the various components did not. He folded wheels, stripped cogs, and generally wore the bike out in a couple of months. Fast forward to now. He is still riding. He is still huge ( now about 450). He rides a Rocky "Flow" now. It seems to be holding up just fine. Jason gave up trying to ride off road. He sticks to the street. So, I guess the frames themselves are rugged enough for up to 500 pounds, but the components may not be.