A brief lesson in tyre sizes

A brief lesson in tyre sizes

For this lesson we will us the size: 205/55R16 91V as an example.

We will break this down into manageable pieces:

205 = This is defined as the tyres “nominal inflated section width”, in English this is the width of the tyre measured in millimetres in this example 205mm when the tyre is inflated.

55 = This is called the “aspect ratio”, this is the height of the tyres' sidewall shown as a percentage, in this example the tyres sidewall height is 55% of the tyres' 205mm width.

R = This is quite straightforward with todays tyres, this means the tyre is of a radial construction. In days gone by there were a number of options.

16 = This is the “rim diameter”, in basic terms the size of the hole in the middle of the tyre that the road wheel fits on. This is measured in inches.

91 = The tyres maximum load capacity. This gets a little more complicated as it refers to a chart where 91 means that this tyre can carry 615kg. It is very important to get this right as when this is calculated over every tyre it gives you the vehicles maximum carrying capacity.

V = This is the speed index, again relating to a chart of which a maximum 'sustained' speed cannot be exceeded, in this example it is 149 mph.

Tyre labeling

Tyre labeling

The new EU tyre label provides important information about safety and environmental aspects of a tyre. Similar to the energy label found on kitchen appliances, the EU tyre label makes it easy to compare tyres in terms of wet grip, fuel efficiency and noise.
Fuel efficiency
A measure of the tyre’s rolling resistance, which has an impact on your vehicle’s fuel efficiency. Rated from A (highest rating) to G (lowest rating).
Wet grip
A measure of the tyre’s braking ability on wet roads. Wet grip is rated from A (highest rating) to F (lowest rating).
A measure of the external noise generated by the tyre, in decibels. The black sound waves indicate the noise class of the tyre, from 1 (quiet) to 3 (loud).

Reading your tyre size

Understanding tyre size

The numbers and letters on the side of a tyre can seem like Egyptian hieroglyphics but each and every part has a particular meaning that is essential to you getting the correct tyre on your vehicle ensuring that the driving characteristics are retained and that you remain safe and legal.


It is incredibly important to get all of these factors right when replacing your tyres, in some cases it could mean an MOT failure. When choosing your tyres our best advice is to check the ACTUAL tyres on your vehicle and not to use either the vehicles’ handbook or a registration number checker on some websites, as vehicle manufactures or previous owners may have changed the specification on ‘your’ car.

Or, ring or call in to tyrZ for a FREE no obligation check.