how to read tyre size

What Does 225/40R18 Mean? A Complete Guide To Tyre Sizes

225 = tyre width | 225mm
40 = sidewall profile | 40% of 225
R = radial construction
18 = rim diameter | 18 inches
refer below on the indept explaination with images

Learn how to read tyre sizes such as 225/40R18. Understand tyre width, profile, rim diameter, load index, speed rating.

On your tyres, you’ll see numbers like this: XXX/XX R XX (refer to the image below). Some tyres may not display the markings as clearly as shown, so take a careful look to identify them.

The first number indicates the tyre’s width in millimeters
example below (225/40R18)
225 → Tyre width in millimeters
225 means the width of the tyres is 225mm

first number of tyre

the second number represents the aspect ratio
The sidewall height as a percentage of the tyre’s width.

example below (225/40R18)
the sidewall height is 40% of 225 mm
(which equals about 90 mm)

tyre aspect ratio meaning

the third number is the rim size in inches.
example below (225/40R18)
rim size is 18 inches

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Beyond the basic tyre size, you’ll also notice additional letters and numbers printed after it. Each of these represents information about your tyre’s capabilities. They are the tyre load index and tyre speed rating

Numbers and letter after your tyre size. what these actually means
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  • Load Index (number): This indicates the maximum weight a tyre can safely carry when properly inflated. This is especially important especially with the raising of EV.
    For example, a load index of 91 means the tyre can support up to 615 kg. The higher the number, the greater the load capacity. (refer to table below)
  • Speed Rating (letter): This shows the maximum speed the tyre is designed to safely sustain under load. For instance, V means up to 240 km/h, while H means up to 210 km/h. The ratings progress alphabetically, with higher letters generally representing higher speed limits.(refer to table below)

tyrespeedload
image from Goodyear

👉 Together, the load index and speed rating ensure your tyres are matched to your vehicle’s weight and performance requirements.

CASE STUDY

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EXAMPLE 215/60R16 99V

215 = 215mm in tyre width
60 = 60% of 215
16 = rim size is 16 inches
99= per piece tyres are designed to support 775KG
V= tyres are designed to perform up to 240KM/H

 

Tyres FAQ

  1. Do EV needs special tyres?
    Not exactly but there are few things to look at , check out our EV page HERE