1. Worn Out Surface
All tyres come with tread-wear indicators (TWI), which is a bar-shaped bump located in the grooves. The indicator helps you determine whether the tyre has reached minimum wear level (1.6mm or 2/32 “). If the bump bar is visibly level or close to level with the surface, that’s when you need to replace the tyre.
2. Cracked Tyres
Look for cracks on tyre treads and sidewalls. Minor cracks are acceptable, but they are early signs or wear and tear. If cracks are found, keep monitoring them to see whether they get worse. The best thing to do is still to replace them, better sooner than later..
3. Reduced Traction
Tyre compound hardens eventually due to repeated heat cycle, thus reducing grip. Even if your tyres look fine, if it does not perform as expected, especially when under braking, you should replace them as soon as possible.
4. Swollen Tyre
If you detect unusual vibration when driving, especially at low speed, you should inspect your tyres to see whether they are swollen. This signals damage to the internal structure. It is downright dangerous to drive on swollen tyres. They must be replaced immediately.