My wife passed her test at a driving school, and was pleased to show me the date on my tires, "can only be 4 yrs old'' she said proudly, Me ''did they show you this arrow for the wear bars" "no" I have often been told at tyre shops you need new. Anyhow this is why I buy the cheap tyres now, keep them coated with a tyre spray and park if pos. out of the sun and keep the pressures correct, check the side walls often.
for those who don't know wear bars.