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Tyre sizes explained: what do the different sizes of tyre mean?

The sidewall of a tyre is loaded with key information. Here’s everything you need to know about tyre sizes

Tyre on workshop floor

You’d be forgiven for not paying too much attention to the markings on your tyres. These days, you can order a set of new tyres simply by sticking your car’s registration number into a website, which is like a cheat code for decoding the various numbers and letters that appear after the manufacturer and product name on the tyre’s sidewall.

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But what happens if you need to order a set of tyres without access to a website or you’re trying to work out the size and spec of the tyres on your car. This is where our guide to tyre sizes comes in, but for more detailed information check out our tyre markings and labelling guide, which tells you how to read a tyre’s makings in full.

How to read your tyre size

The six key elements of a tyre’s size can be found on the sidewall, often after the manufacturer and product name. For this guide, we’re using one of the most popular tyre sizes in the UK: 205/55 R16, along with 91V. Let’s break down what this means…

205: Tread width (in millimetres)

The first number represents the width of the tyre in millimetres between the inner and outer sidewalls. In this case, the width is 205mm.

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55: Aspect ratio (percentage)

The second number shows the height of the sidewall as a percentage of the width. A lower number indicates a shorter sidewall and is often found on sports cars or those designed for sportier handling, often at the expense of ride quality. In this case, the sidewall height is 55% of the 205mm width.

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R: Radial construction

Radial construction is the most common type of tyre construction and refers to the use of steel and kevlar belts to reinforce the tyre carcass. It also helps to increase tread life, reduce rolling resistance and improve fuel economy. Other tyre constructions that you might see include B for bias and D for diagonal.

16: Wheel diameter (in inches)

This number denotes the size of alloy or steel wheel the tyre is designed to fit, measured in inches. In general terms, a larger wheel diameter can result in a less comfortable ride and increased fuel consumption, but this isn’t always the case. In our example, the size of the wheel is 16 inches.

91: Load index

The load index is the maximum load a tyre can support, but you’ll need a separate table to find the actual figure. In our case, a rating of 91 means the tyre can support a load of 615kg. At the extreme ends of the index, 65 means 290kg, while 108 corresponds to a maximum load of 1,000kg. The higher the load index, the more weight the vehicle can carry.

Tyre load indexWeight in KGTyre load indexWeight in KG
6529091615
6630092630
6730793650
6831594670
6932595690
7033596710
7134597730
7235598750
7336599775
74375100800
75387101825
76400102850
77412103875
78425104900
79437105925
80450106950
81462107975
824751081000
83487  
84500  
85515  
86530  
87545  
88560  
89580  
90600  

V: Speed rating

The speed rating indicates the maximum speed the tyre can safely handle under optimal conditions. In our case, a V rating means the tyres can handle speeds up to 149mph. Other common ratings include H (130mph) and T (118mph), while at the extreme ends of the speed rating table you’ll find N (87mph) and Y (186mph). 

Speed ratingMPH
Q99
R106
S112
T118
H131
V149
VR131
W168
Y186

These are the six elements of the tyre’s size you’ll need to know when ordering fresh rubber, but check out our guide to tyre markings and labelling for more information on specialist tyres, rolling resistance and OE markings.

Now take a look at our guide to tyre speed ratings...

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