My buddy from the State patrol sent this, and it's the same as what Binder posted above.
State Patrol said:All tires and rims must meet the federal motor vehicle safety standards (FMVSS) in order to operate on the public roadway. Each manufacturer should have them certified through the USDOT if they meet these requirements for road use. If the tires/rims say for off road use only, then they are not legal to use on public roadways. There are two applicable federal standards regarding vehicle rims (depending on the vehicle size) FMVSS 110 and 120 which are attached.