Hi, after about 3 to 4 years on my original Canadian Marathons, I noticed two on the street side with bubbles, one bubble each. One bubble was on the outside and about 3" diameter. The other bubble was on the inside and was oblong, maybe 1 1/2" X 3"s. Goodyear would not warranty them; They say I ran over something. [B.S. excuse to not warranty them] Anyway I bought two more Marathons. These were Chinese made. So my curb side and spare are original Canadian Marathons, and my street side are Chinese Marathons. I have not had any other problems, I drive at mostly 60 to 65 MPH, and keep them at 65 lbs pressure. This last weekend, on the way up we saw a few vehicles on the side of the road with flat tires. On the way home we saw several vehicles, one fifth wheeler, with flat tires. We actually saw two vehicles moving to the right of the FWY as their tires just came apart. I say we dodged the bullet, no flats for me. I do check my tires, visually, at home and at all rest stops, gas stops, and camp grounds. My tires to date don't have any cracks in them. People who have the same year trailer as mine, or newer, have replaced their tires due to cracks. The big question is: Why do some of these tires last so long without problems and others crack up or fall apart in 2 years or less?