Tyres should also be inspected for wear, cracking, bulging, or objects caught in the tread. If excessive wear, cracks, bulging, or deep cuts are found, the tyre should be replaced.
Most new tyres have a built-in tread wear indicator. When wear indicator is approaching contact with the road, the tyre should be replaced.
The UK law states tyres must havea tread depth of at least 1.6mm across the central three-quarters of the breath of the tread and around the entire circumference, however many manufacturers recommend changing at 2-3mm. You can buy an easy-to-use tread depth gauge to measure the tyre tread depth.