When do I have to replace the tyre?
1. When it is worn.
The legal limit for the tread depth on the 3/4 of the tyre surface is to be more than 1mm at any point. While the rest of the 1/4 should have visible tread.
2. Has a damaged sidewall.
Sidewall is not allowed to have any cracks, damages or tears even if it is repaired.
3. Too old
As rubber doesn't age with grace, the older the tyre is the harder it is hence it loses it's grip. As a rule of thumb, any tyre older than 10 years old, irrelevant of the tread depth, is recommended to be replaced.