According to DOT you must have it tied on with devices which equal the weight of the vehicle and must be tied so it cannot move forward, aft, sideways or up. In the trucking business we tied them on all 4 corners at a 45 degree angle and used the strap that goes over the tire. You can then tell if you have it tight enough because the tire will begin to flatten out some. If you should roll over and it comes loose, you get a ticket for unsecured load. Insurance won't pay a dime. If it stays on the trailer you may have won a small battle and consolation knowing it stayed on.