When should I replace my tires? Have you ever felt that your tires weren't working as well as they did before, but once you look at them they appear to have tread on them? Tire change during their in service life. The two main factors that contribute to a tire's aging performance -
Tread depth - Legal minimum tread depth is 2/32". In our in-house testing, I have found that tires are no longer suitable for snow below 5/32". Hydroplaning resistance suffers below 4/32". Check out this video!
Heat cycling - Something offered to enhance the 1st day performance of race rubber. It also explains why tires' grip goes away in the last 1/3rd of their life.
As rubber gets more firm from heat cycling it looses it's mechanical compliance to the pavement surface. This is why wet pavement traction goes away in the last 1/3 of a tires' life.
Heat cycling also explains why high performance tires feel sporty in the end of their lives, the lack of tread blocks flex.
When you get a new tire, the tread blocks are tall and soft compared to short and firm. This is why a brand new performance tire doesn't feel as good under an aggressive cornering maneuver.