We have towed on a set of Marathons, Load Range C, for 30,000 miles with no problem -- rough Calif. freeways, rocky roads, hot weather. We did not exceed 65 and usually towed at about 62.
They showed a little wear, and they were four years old, so I just replaced them with the Endurance, Load Range D. I probably could have gotten another year out of the Marathons, but I am inherently risk-averse.
We have run Marathons for 4 years without problems and am guessing about 8,000 miles. I wish they were American made but they are not.
Thank you. If we think about it, we use many foreign products that turn out to be just fine. But we forget that. We can't generalize I guess.
A lot depends on who operates the foreign factory. Goodyear being an American company will operate a foreign factory pretty close to how it operates in the US. Factories operated by owners in the country of origin not so much.