Tyre Size Explained: How To Read Your Tyre's Sidewall

On the side of every tyre produced, you'll find a series of numbers that identify your tyre size. These numbers are vital to the safety of your daily drive.

But how do you measure a tyre? Where do you find your tyre size exactly? Tyroola's guide will explain all things tyre size and decipher the secrets of your tyre sidewall.

Where can I find my Tyre Size?

Every vehicle has a specific tyre measurement that can be found on:

  • the tyre sidewall
  • the manufacturer’s placard inside your driver's door or glove box
  • your owner's manual

When purchasing new tyres, always double-check that they are suitable for your vehicle and follow any load and weight ratings recommended by the law.

What are the numbers on my tyre sidewall?

The series of numbers found moulded on the sidewall rubber of your tyre provides valuable information about tyre size and dimensions, its purpose, load capacity, and speed durability.

These numbers consist of the following:

  • Type of vehicle
  • Tyre Width
  • Tyre Profile or Sidewall Aspect Ratio
  • Tyre Size / Diameter / Rim
  • Load Index
  • Speed Rating

Tyre Size

The two ways of measuring tyre size

    1. Via tyre diameter    

    2. Via wheel or rim size

The difference between these two measurements on the same tyre is approximately the height of the tire’s sidewall. Unlike the width, tyre diameter and wheel size are generally measured in inches. This measurement comes after the aspect ratio number on your tyre's sidewall.

The most common method of tyre size measurement is the wheel size measurement

Tyre Size

First Letter: Type of vehicle

The first letter on your tyre's sidewall identifies the type of vehicle and the service it’s designed for. The common Letters indicate the following:

  • P: P stands for ‘Passenger’ vehicles and covers cars, minivans, sport utility vehicles and light-duty pickup trucks, (typically 1/4- and 1/2-ton load capacity).
  • T: T stands for a ‘Temporary Spare’, or ‘space saver’ only designed for temporary use until the original tyre can be repaired or replaced.
  • LT: LT stands for ‘Light Truck’ meaning the tyre is designed to be used on vehicles capable of carrying heavy cargo or towing large trailers. This includes medium and heavy-duty, (typically 3/4- and 1-ton load capacity), pickup trucks, sport utility vehicles and full-size vans.


Tyre Width (165)

This number measures your tyre's width and is in millimetres. It measures from the outermost point of the sidewall all the way across the tyre tread to the outermost point of the opposite sidewall (facing the tyre well).


Aspect Ratio (55)

The tyre's aspect ratio measures the height of your sidewall and is shown as a percentage of the tyre width. So a sidewall height that is 55% of the tyre width is written as 55.


Tyre Size / Diameter / Rim (17 on the sample above)

The tyre diameter or wheel size follows, which is measured in inches. To find out the range of tyre sizes that can safely fit your vehicle, consult your owner's manual.

Take note: If you want to change your rim size, your tyre diameter should remain the same. You can also double-check your owner's manual or check with the manufacturer.


Load Index (94 on the sample above)

The tyre's  follows, usually as a 2 to 3-digit number and measures the load capacity or maximum weight your tyre can carry at full speed. See chart below for corresponding weight.


Last letter: Speed Rating (H on the sample above)

The last letter represents the or the maximum speed your tyre is designed to handle. It states the absolute limit to how fast your tyre can go before it starts to fail. Each letter corresponds to a certain speed as seen in the chart below.


load index

The speed rating of a tyre is displayed on the sidewall of your tyre within the tyre code. After the Load Index is a 1 to 2-digit/letter combination representing the Speed Rating.


Speed Ratings


Find the perfect tyre for your ride at Tyroola

Tyroola has the widest range of tyres available online. You're sure to find the right tyre size you need. Simply fill out our tyre configurator, and choose the tyre that will best fit your vehicle.


In Summary

Finding your tyre size can add to the stress of choosing new tyres.

Don't worry. Check the tyre’s sidewall and confirm with the info on your owner's manual and vehicle placard.

At Tyroola, finding your tyre size and the right tyre has never been easier!

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