I have 1 tyre that has a chunk out of it (I blame the missus in the co-op car park meself!). Now, I know that the recommenedation is to change at least an axle set (prefereably all 4) but they have done about 3K miles and are not very worn - it would be useful to have a guide as to how much difference in diameter a tyre should be below in order to not change both on an axle ...

Cheers
Paul