a while back i discovered that my 4 yr old/never used spare tire was all cracked up due to sunlight/uv exposure. decided to check boat tires and they had small cracks too. ( namco/made in china junk ). the size was st 165-80x13.... a very knowledgable dealer said that size was no longer made and so i baught the next bigger size.st175-80x13. .but my fender mounts are welded on and the taller tires were close to rubbing the fenders. spent 4 hours rerigging my fenders to accomadate the larger tires. what a pain .if you have a spare mounted to your trailer ,i reccomend you get a cover for it. going out to find 1 now.