Tires older than six years old start dry-rotting
Even though you show good thread life on your old tires, dry-rot can be claiming your tire's life and performance due to age and exposure to the atmosphere's U.V. rays and other natural aging processes. Usually, tires older than six year should be replaced, regardless of the life shown on the threads or blocks. Either way, the safety of dry-rotted tires and compromised and can be just as dangerous as a tire with no thread left on it.