There a several key indicators that will help determine when your tyres may need changing.
A noticeable deterioration in performance can often be due to tyre wear. Your car not handling or gripping the road as well as it normally does, or it taking longer to stop when braking can be tyre related.
Because tyre wear, and therefore a decline in performance are gradual, it is recommended to check your tyres fortnightly and ideally have an expert check them at regular intervals.
Legally, it is the driver's responsibility to ensure that the tread on your tyres is not worn beyond the legal minimum limit of 1.6 millimetres over the central 3/4 of the tyre in a continuous band around the entire circumference of the tyre. It is worth noting that The Royal Society for the Prevention of Accidents (RoSPA) recommends changing at 3mm.
There are many different reasons for tyre wear. The illustrations below show the different types of common tyre wear, and an explanation for each.
Under-inflation causes the tyre to wear on the outer edges of the tread, leaving the central tread area far less worn. Although there is still plenty of tread on the tyre, the middle ¾ has to be 1.6mm or above to be legal
Over-inflation causes only the central tread area to be in contact with the road causing rapid or crown wear
A typical example of the wear pattern caused by front wheel misalignment, (Toe-in or toe-out). The edge of the tread has worn progressively from one side
Excessive wheel camber causes sloping wear on the outer edge of the tread on one shoulder of the tyre
This tyre has been used well after reaching the legal minimum tread depth of 1.6mm across the central ¾ of the tread, going around the complete circumference of the tyre
End Of Life
This tyre has reached the legal minimum tread depth of 1.6mm across ¾ of the tyre tread or more
An emergency braking manoeuvre with this tyre has caused the tyre to rapidly wear through the complete casing causing the tyre to deflate
Sharp objects can cause considerable damage rendering a tyre unserviceable
This is damage caused by an impact to the sidewall. The bulge or "egg" indicates localised casing damage