The NHTSA says that you should inspect more frequently after 5 years due to ozone degradation which accelerates aging. That suggests that tire life deteriorates quickly after 5 years. I have owned ST tires 6+ years before they failed. I have never owned a motorized vehicle that the tires were not worn out on in 5 or less years. Maxxis warrants their ST tires for 5 years. I have heard that some ST tire makers suggest replacing after 3 years but I have not verified that and I would not own tires from a maker who thought so little of their own product.