The Thule bike-rack literature says to not carry four bikes when the carrier is used with a Class I receiver. My work-around was to reduce the sway and tongue weight by using ratcheting straps. The Mazda 5 doesn't have a roof rack, so I installed a couple of nylon straps w/ eyes to attach the ratcheting tie-down strap to. The other end of each eye strap is bolted to the top attachment point for each rear hatch strut. Foam pipe insulation protects the paint on the hatch from the straps.