Here’s our complete guide to tire load and speed ratings

Like any product sold to the public, tires are subject to very strict standards to ensure the safety of a vehicle’s occupants, but also, by extension, that of other road users. These standards fall into two categories: load index and speed rating. These behave like the certifications that all tires must have in Canada. They guarantee that the tires behave optimally with respect to the car they are mounted on when used within the limits indicated by the aforementioned ratings. Blackcircles Canada tells you everything you need to know about load and speed ratings, so you can make the right tire choice when it’s time to get new tires!

The speed rating is more complex. According to the Tire and Rubber Association of Canada, the speed symbol is a letter that represents the maximum speed at which a tire can be driven safely for a predefined load index. Thus, the value of the speed rating depends on the load index. These letters are all listed in the speed index correspondence table below, and represent a range from 5 km/h to 300 km/h.

The definitions detailed above for load and speed ratings have important implications for the occupants of a vehicle, first and foremost for the driver.

For the load index, it is simple: both running gears must have tires that are capable of supporting the load on each of them. If tires with a lower load index are fitted, these will not be able to support the axles properly. They will undergo structural deformation that may affect their integrity. In addition to shortening their service life, this structural deformation can be dangerous in driving situations, since it affects the vehicle’s behaviour during acceleration, braking and cornering. For this reason, it is strictly forbidden to fit tires with a load index lower than that of the original equipment or that prescribed by the manufacturer.

These ratings are valid only for original equipment tires with integral structure, inflated to the correct pressure and mounted on a vehicle with a load that complies with the tire load index. They also represent a standard of longevity, represented here by the tire’s ability to resist heat or temperature rise. Tires rated with higher speed ratings usually dissipate heat better, grip and perform better when turning or braking. They therefore give a more rigorous road handling to the vehicle equipped with them.

Unlike the load index, the speed rating offers more manoeuvring freedom. Thus, during the summer months, while it is forbidden to fit a tire with a lower speed rating, it is perfectly possible to fit one with a higher index than the original recommended level. In winter, on the other hand, it is possible to opt for tires with a speed rating just below the minimum speed rating recommended by the manufacturer for summer tires. The reason: lower driving speeds and colder weather during the winter season. However, as soon as the temperature regularly stays above 7 °C, you will have to return to your summer tire fitting. One last thing: prolonged driving at high speeds can damage tires and cause an accident, even if they are inflated to the correct pressure and mounted on a vehicle with the appropriate load. So be careful!

Now that you know exactly what the load and speed ratings are for a vehicle and why they are important, you need to identify them on your vehicle’s tires.

It’s very easy to find them; simply look on the sidewall of your tires for a code made up of numbers and letters based on the following model: 111/1A11 11A. Let’s look at a concrete example, with the 195/65R15 91H code.

In the example above, you will need to look at the last two numbers to determine the load index, and the last letter to determine the speed rating. You will then have to refer for each of them to the corresponding value respectively in the load value table and the speed value table below to find out the maximum load and speed for which your tire is approved. Here, the load index corresponds to a maximum weight of 615 kg, and the speed rating to a speed limit of 210 km/h.

Now you know what the load and speed ratings of a vehicle mean and what they mean for your safety. Once you have identified the load index and speed rating for your car, the next time you change your tires, make sure they meet the minimum recommended values for your vehicle. However, if it’s already time to change your tires, visit blackcircles Canada’s website to find the right ones for your vehicle and place an order!