I just bought a Reese 'Backpacker' trailer to carry my wife's mobility scooter. It is extremely light and will fit my needs. It comes with 8" tires that I would like to replace. I have the room to replace the 8" tires with 12' inch tires. Most of my towing would be at 'freeway' speeds over long distances. My question...would the 12' size be better and should I get bias ply tires over radial tires for highway towing. As always, TIA for any help or information.