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Decoding the writing on tires

At first glance, the writing on your tire’s sidewall may seem like an amalgam of random letters and numbers. But that alphanumeric jumble can tell you a lot more than you than expect.

advantage car blog decoding tire writing sidewall

In fact, learning how to read tire numbers will give you great insight into the exact type and size of your tires as well as enlighten you of safety standards. The world over, tire sidewalls are lettered with letters and numbers that identify the width, loading capacity, operational capability and other information of the tire. So when it’s time to change your run-down tires, you can easily identify the appropriate replacement based on the writing on the sidewall. So what do tire codes mean? Read along to find out more about decoding the writing on tires!

When you rent a car from our car rentals desk in Mississauga, you know that our cars are shod with rubber for that season. Just check your tires and you’ll see we’ve got winter tires on the moment temperatures dip below 7°C.

Tyre specifications chart and tire codes

Read our tyre specifications chart and explanation of tire codes below to learn to read the numbers on your tires. It’s a fascinating exercise and will really make you think about what tires are right for your driving.

Tire size: this is a sequence of letters and numbers, coded to identify your tire’s type, width, aspect ratio, construction type, wheel diameter, load index, and speed rating.

Type: this comes as the first character in your tire size and it is used to determine the tire’s class. So a “P” indicates it’s a passenger tire, which is popular in most cars. Whereas “LT” stands for light truck and along with “ST”, special trailer, these tires are used in vehicles designed to carry heavier loads and are generally found in trucks, big SUVs, and off-roader. On the other hand, no letter preceding the size means it’s a European metric tire.

Width: this is the measurement of a tire’s width, taken from one sidewall to the other, in millimeters. The bigger the number, the wider the tire.

Aspect ratio (height: width): the aspect ratio of a tire is the height of the sidewall, except it’s not measured in millimeters, but rather represents the height as a percentage of the width. So, if the sidewall says 235/60, it means the width of the tire is 235mm and the sidewall is 60% of that – 141mm. A low profile tire is one which has a smaller sidewall; a high profile tire will have a bigger sidewall.

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Construction type: one of the most prevalent types of passenger or truck tires are radials. In these tires, the internal plies are perpendicular to the direction of travel. In some older cars (mainly vintage ones) you might find a “B” instead of the radial-ply tire’s “R”. This stands for bias-ply, where the cord plies overlap each other, running at a 45-degree angle from bead to bead.

Wheel diameter: this indicates the width of the rim, either in inches or centimeters,  that the tire has to be mounted on.

Load index: the load index represents the maximum weight that a tire can safely handle at its maximum inflation. Most passenger car tire loads range from 75 to 100, though some are higher. So a 75 load index means the car can safely carry 852lbs, whereas a 105 load index entails that the car can handle 2039lbs.

Speed rating: the speed rating of a tire indicates the maximum service speed your tires can travel while loaded. A “Z” rating means that the tires have been tested over 149mph. While a “Y” rating translates that the tire has been tested over 186mph, though it doesn’t specify how much above the given rating. But this is in no way indicative of the recommended speed your tires should travel at, as you still need to respect speed limits.

Winter tires

You might find other symbols in your tires, for instance, a three-peak mountain snowflake symbol would indicate that your tires perform well in winter conditions. While tires marked with an “M+S” symbol (mud and snow) means that they are all-season tires. However, these all-season tires are not approved by the Tire and Rubber Association of Canada for use in winter conditions, since they lack the improved traction needed to travel in extremely low temperatures.

 

Our Mississauga car rentals desk can help you find out more about the tires you are on, so you can drive safer. Remember this: the entire weight and performance of your vehicle is transmitted through the tires, so they need to be in very good condition!

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