How do you know when to replace your tyre??
Here is a simple test but you need a penny(Little difficult to find or we need to explore some indian coin )
This technique involves placing of penny inside your tyre groove with Abraham lincoln face visible to you as shown in this pic(select the most wornout portion of the tyre).If Abraham lincoln head is covered by your tyre groove then you are driving with a safe tyre else technically speaking you need to replace the tyre.Because as per standards you need to keep at least 1/16 of an inch as your tyre groove depth and the space b/w the edge of the penny to Abraham lincoln head is exactly the same
So if you have a Penny with you,you can Drive safe but you need to find one.
There is one more method which is found on new tyres as shown
They are called 'Tyre wear bars' which are placed in between the grooves of tyres.So if your wear bars started Wearing its time to replace your tyres.But unfortunately it is still not available India. I wonder when we replace our tyres, ever we thought of such a test!! :)