Don't know if this will help anyone but if you have an older set of Goodyear's it might be worth a call. Apparently there was a "silent recall" some time ago on these. I read this on a trailering forum:
Goodyear will adjust the old type Marathon, Load Range "D", ST 225 R75/15. The old tire does not have a circled "S" after the word radial on the sidewall. The new tire does. In many cases they will replace the old tire at no cost, or maybe a small fee for mounting an balancing, it depends on tire wear. If you have the old type ST 225 R75/15, Load Range "D", call Goodyear @ 800-321-2136. They will direct you to your local dealer. They replaced one tire for me and five for a buddy of mine, no questions ask. It cost me nothing and my buddy paid $40.00. Goodyear advised me that the ST 225 R75/15 Load Range D was the only tire that was affected.