Bicycle Tyres and Wear

From Bicycle Defects

The tyre on the left has just hit the 7000Km mark. I purchased the tyre on the right a couple of months ago but a friend suggested I not change it till you "could see the canvas".

What is more likely to happen is that I will start getting punctures, but so far, fingers crossed.

Both tyres are Schwalbe Marathons, good value for money.