Our current Marathons ST225/75R15D's have about 40,000 km (25K miles) on them. They are 3-4 yrs old from date of manufacture in China. Original rubber valve stems and balance.
No problems so far and lots of tread left. Because of the high mileage, I do rotate them, including the spare, every year. Usually travel ~62mph (100km/h). Check the pressures ... occasionally, when I remember.
