I suspect most frames will support riders OK up to the high 200 pound weights, but issues like too much flex might be much amplified at those levels. Anything heavier and there's a good chance the person might be just too large to ride a conventional bike frame anyway......so it branches out to special custom bikes designed with special geomtries and heavier gauge/larger OD tubing....kinda like special "Bariatric" equipment and furniture now manufactured for healthcare facilities, where the design and materials are chosen specifically to carry a larger/heavier than "normal" load....