Hi Mike....good question, and the answers are right. There were a few with frames, but as the drive gear got ruggeder, they dropped the frames. I got an old Crestline Publishing Encylopedia of American Farm Tractors, copyright 1979 that shows if not talks about the evolution of early tractors. I looked through it but couldn't find the statement I thought I read....maybe another book. If you aren't familiar with the Crestline series, they are hardcover B&W books with lots of pix, and are published for a lot of transportation themes - Military Wheeled Vehicles, the big name auto manufacturers, etc.. They are mostly good for ID-ing something, not a lot of tech info on one particular model. I usually wait until the local bookstore puts one out for ten buck or so (got one for $4.00, once), because I can't see paying full price.