Federal Motor Carrier laws only apply to interstate vehicles in commerce, states adopt those federal regulations for intrastate commerce and can have their own state requirements for licensing for recreational use. For example, here in Colorado you can drive a Class 8 big rig around all day long with a 53' Semi Trailer attached on a regular license as long as you are not being compensated for it in anyway, the minute money changes hands or compensation of any kind is recieved you need to have a Class A cdl for the combination I just mentioned. So unless your state has their own licensing requirements for recreational/personal use vehicles, you can drive as heavy of a truck as you want.