9 year old tyres would also have been dangerous. The compound as you observed with the new tyres had hardened on the old ones.
I usually change them after 6 years
I agree John. It is a new car to me so tyre changing from the safety aspect was one of the first items on the list. As I say I was just stunned by the amount of the difference in comfort.
Speaking to a friend in the tyre business at manufacturer level he said that the number of heat cycles is the real arbiter. Once they have been through a certain number of heat cycles (through normal use) then they've had it! Age is given by tyre makers as a proxy for number of heat cycles I guess.
