Why is it important to learn to read the tyre size of your car?

by Editor News

Hey, I'm Pallavi from Tyrezones and today I'm going to teach you about what all the numbers and letters on the side mean written on the sidewall of the tyre. It is important for every vehicle owner to know how to read the tyre size. One of the cool things about tyres is that its sidewall actually tells you everything about the tyre. One of the things that I find really interesting is that the tyre actually tells you how old it is. Knowing the year and the month in which a tyre was made becomes useful if you're buying a used set of tyres from a junkyard or something like that. Even if you're buying a set of brand new tyres from a store you should know how to find out how old the tyre actually is because sometimes new tyres in a store are actually a couple years old. Therefore, it is always kind of important to watch out for that, especially at a place where you're getting a really good deal on tyres. One shouldn't buy old tyres because of the expiration of the tyres.

To figure this out, you should see the sidewall of the tyre. The side of the tyre has some numbers written on it, and if the tyre was made before the year 2000 it's a three-digit number. The number denotes the week of the year and then the year that it was made. For example, if a tyre was manufactured in the 16th week of 1996, then the number written on it would be 166. However, if a tyre has been manufactured after 2000, it has a four-digit number written on it. So in this case, if a tyre has been manufactured on the 16th week of 2007, it would have the number 1607. Tyre manufacturers started using these four-digit codes to avoid confusion between decades. The year ‘7’ in a three-digit code could mean 1987 or even 1997. Using the last two digits of the year avoids confusion.


One of the most important things about a tyre is the tyre size. For example, if the number written on the sidewall of the tyre is 235/55/17, 235 would mean that the tyre is 235 millimetres wide. So, the more millimetres, the wider will be tyre and vice-versa. The number 55 denotes the height of the sidewall. In this case, it's 55 per cent of 235. The height is always a percentage of the width. The number 17 is the diameter of the wheel itself, and so, in this case, it's a 17-inch wheel. If there is an ‘R’ written on the tyre, it means that it is a radial tyre. Pretty much all tyres these days are radials. Therefore, 235/55R 17 is the actual code written on the sidewall.

Another really important factor about tyres is the load rating, the speed rating and the type of tyre it is. For example, if the side of the has ‘99 W M+S’ written on it, it means that 99 is the load rating. This means that the tyre can handle one thousand four hundred and seventy-seven pounds on that one tyre. If you multiply that four times and your car weighs less than that, then the tyres are good to go, but, if it weighs more than that you're overloading your tyres and it's unsafe to use them. W is the speed rating that means these tyres can go 168 miles per hour safely. The higher the letter, the faster you can go. The speed rating is pretty important, especially if you take your car to the race track or anything like that. M+S stands for mud and snow that's what most tyres are. If you go look at your car right now it probably has an M+S on the side of it. It's pretty much a good all season tyre. You can buy strictly winter tyres or strictly summer tyres, but M+S is the pretty standard all season tyre.


Right next to the tyre size there is ‘99 W M+S’ written. This means that 94 is the load rating. The Q is the speed rating of 168 miles an hour and the M+S is the mud and snow. Taking this example into consideration, this is basically an all-season tyre.

On the side of the tyre, you'll find the maximum inflation pressure. This is not the pressure you set your tyres to. This is the maximum amount of pressure that the tyre can handle without exploding or at least becoming dangerous. For example, if the max inflation pressure of a tyre is 44 psi, that's not what you set your tyres to, that is the maximum that they can handle. As far as pressure goes, one should always follow the instructions on the car door, in the door jamb. The tyre pressure for every car is different. It is usually between 28 psi and 36 psi, sometimes higher sometimes lower. Heavy trucks have very different tyre pressure and the same with trailers. So once again the max tyre pressure is not something that you want to put in your tyre.

The last thing worth mentioning as far as tyres go is the sidewall of the tyre. In our example, the sidewall of the tyre is 45. This is also the most important part of a run-flat tyre. If you have one of the newer cars that have run-flat tyres, the sidewall of the tyre is actually thicker and it allows it to be driven well. Even though there's no air pressure in it you can still drive it to the nearest gas station or shop to get it repaired or at least put some air in it a normal tyre.



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