My trailer had the 12" 480 bias ply tires when it was new. I blew one on the highway within a year so I put the 510 bias ply tires on to handle the weight. These don't last as long as I would like and I don't trust them on long trips so I would like to find a radial tire that would fit. I was told the Ford Fiesta tires are 12" and they would fit on my bias ply rim. I saw the Marathon radials but the smallest they make are the 13" tires. Anyone know where I can get a radial 12" tire to fit the trailer? Are bias ply tire rims with an innertube the same as a radial tire rim?