One sign that your tyres need changing is usually under performance. For example, your car does not handle as well in poor weather conditions as it normally does, or it takes longer to stop when you apply the brakes.
It's the driver's responsibility to ensure that the tread on your tyres is not worn beyond the legal minimum limit of 1.6 millimetres.
To make this easier to identify, tyre manufacturers mould tread wear indicators (T.W.I) into the design of the tyres tread pattern usually at 1.6mm. As soon as the tread is worn to the height of the tread wear indicator, the tyre has reached the legal minimum tread depth and you should replace the tyre as soon as possible.
You should also be aware that there are many different reasons for tyre wear. Your tyres don't just get worn through age and use, but through emergency braking, under-inflation or over-inflation. And if your wheels are misaligned, one edge of the tyre can wear more rapidly than the other edge.
UK law requires that your vehicle is fitted with the correct type and size of tyres for the vehicle type you are driving and for the purpose it is being used. This means fitting the right tyres, and for safety ensuring that they are inflated to the manufacturer's recommended pressure.
The legal limit for minimum depth of the tread on your tyres is 1.6 millimetres, across the central ¾ of the tread going around the complete circumference of the tyre.
For safety reasons it is recommended that you replace your tyres before the legal limit is reached. Leading motoring organisations recommend 2mm and many vehicle manufacturers recommend replacing at 3mm.
A regular check of your tyres can help you to avoid up to 3 penalty points and £2500 in fines (per tyre) for having tyres worn beyond the legal minimum limit fitted to your vehicle.
It is also a legal requirement to ensure that tyres of different construction types are not fitted to opposite sides of the same axle. The two main tyre types are radial and cross-ply, and these must not be mixed on the same axle.
Mixing brands and patterns of the same construction type is permissible depending on the vehicle type and manufacturers recommendation. Check your vehicles handbook for tyre fitment details and options.