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Tyre Fitting

When to Change a Tyre

If your car doesn't handle or grip the road as well as usual in wet weather or it takes longer to stop when you apply the brakes, this could be a sign that your tyres need changing. Because your tyres wear down gradually it can be difficult to identify these changes so we recommend that you have your tyres checked regularly by a qualified National Tyres and Autocare technician.

Tread depth indicator

This tyre is very close to being - or has just become - illegal

Advice & Guidance on Tyre Tread and UK Tyre Law

UK Tyre Law : Tyre tread and the Law

The law requires car tyres to have a minimum tread depth of 1.6mm in a continuous band around the central three quarters of the tyre. To help you judge how much tread you have on your car tyres, manufacturers often mould tread bars at roughly 1.6mm.

If you can see these bars your tyres are about to become illegal and unsafe. However, for optimum safety, most manufacturers recommend that your tyres are changed at 3mm.

Many manufacturers now include a Tread Wear Indicator (TWI) within the grooves of the tyre tread which become more visible as the tyre wears down. Whilst these markings are an indicator, always check the tread depth using a tread depth gauge and check your tyres regularly for bulges or wear.


Tyre Valves

The tyre valve is often the most neglected and overlooked component within the wheel and tyre assembly, yet an efficient valve is important for the safe operation of the tyre.

Wear on the valve seal, damaged screw threads, dirt and grit in the valve itself can lead to failure of the tyre at speed. Even a poorly sealed valve can cause fairly constant under inflation of the tyre which will reduce the life of your tyre by up to 25%. As it is impossible to replace the valve without removing the tyre casing from the wheel - National Tyres and Autocare recommend that the valves are replaced EVERY time a tyre is replaced.

Reading a Tyre Sidewall

Every tyre sidewall shows information about the manufacturer, size, model etc. Here's a summary of the most important information and what it means.

Example: 205 40 R17 84W


means the tyre has a nominal section width of 205 millimetres


is referred to as the aspect ratio and is the height of the tyre sidewall as a percentage of the nominal section width


means the tyre has a radial construction, the most commonly used of three different types of tyre construction: cross ply, radial and bias belted


means it fits a 17" diameter wheel


is the load index. This identifies the maximum load capacity of a tyre when driven at maximum speed. Overloading a tyre, by carrying more weight than it is designed to or running at a lower than specified pressure can cause heat build up and blow outs. Load indexes for passenger cars usually range from 70 - 110 and the maximum load per individual tyre is shown in the table below


is the speed rating. This represents the maximum speed that a tyre can sustain at full load. The example shown is rated for speeds up to 168mph.

Load Index and Maximum Load per Individual Tyre  

Common speed ratings are


for cars with max speeds up to 100mph (160km/h)


for cars with max speeds up to 105mph (170km/h)


for cars with max speeds up to 113mph (180km/h)


for cars with max speeds up to 118mph (190km/h)


for cars with max speeds up to 130mph (210km/h)


for cars with max speeds up to 150mph (240km/h)


for cars with speeds over 150mph (240km/h)


for cars with max speeds up to 168mph (270km/h)


for cars with max speeds up to 186mph (300km/h)

You should always replace a car tyre with the same or a higher speed rating and we recommend that you check against the speed rating approved by the vehicle manufacturer.

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