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If you ask most people for details about their vehicle’s tires, you will likely not get much information beyond “summer”, “winter”, or “all-season.” What many do not realize is that everything they actually need to know about their tires is actually printed right on the tires themselves. Size, type, and rating are all featured on the tires, but without gaining a bit of relevant knowledge beforehand, it can be tough to decipher what it all means. Fortunately, we here at Westbury Toyota are here to help you out by providing you with everything you need to know in order to be able to shop with confidence when it comes to repairing or replacing your tires.
When looking at the numbers on the tires, it is common to think that they are displaying the width and diameter of the tire. While this is true, there are actually other things denoted by those numbers. First of all, it is going to be a mix of numbers and letters, and the key to deciphering what they mean is to understand what each of them mean. Below is an example:
Every sequence on a tire will always start with a letter first. This letter will tell you exactly what kind of tire type it is. In the example above the sequence starts with a P, which means that it is a passenger car tire meant for SUVs, cars, light-duty pickup trucks, and minivans. The tires are manufactured to meet North American load indexes and standards for all related passenger vehicles. Another example is a sequence that starts with “ST”, and in this case ST stands for “special trailer”, which means that the tire is meant for a trailer. “LT” is for “light truck” and “T” is for temporary (a spare tire).
Now it is time to move onto the next part of the sample sequence given: “215”, which follows immediately after the “P” and is right before the slash. In this instance, the 215 indicates the width of the tire tread, also known as the section width. The section width is measured in millimeters (mm) across the tire from each of the sidewall edges, so in the example given, the section width would be 215 mm. The wider a tire is, the larger that number will be.
The next part of the sequence, which comes directly after the slash, deals with aspect ratio. This is an indicator of the sidewall height as compared to the section width, and it is displayed as a percentage. In the example given above the aspect ratio is 65 percent, so 65 percent of 215 mm would result in a sidewall height of 139.75mm. Once again, the larger the aspect ratio, the larger the sidewall height will be.
It should be noted that tires that have a shorter sidewall (aspect ratio of 55 or less) are meant to offer drivers improved steering and handling response.
Following the aspect ratio in the sequence, you will typically find the letter “R”. This stands for “radial” and it pertains to the tire’s internal construction. To simplify it, radial tires are made of internal ply cords that run radially across the tread and they are perpendicular to the rotation axis. Radial tires are the industry standard due to how much grip, durability and ride comfort they offer compared to other types of tire construction, and they are also better for fuel economy.
Next up in the sequence is the rim diameter, measured in inches. In the supplied example the number is 15, which means that the rim diameter is 15 inches.
Following the rim diameter in the sequence is a space, which is followed by a number that is either two or three digits long. This number is the load index and it indicates the maximum weight each tire can support on its own when at proper inflation levels. The load index starts at 1 and ends at 150, and these numbers refer to weight capacities ranging from 99 pounds (lbs) all the way up to 7,385 lbs. For the example given above, the load index is 95, which means that the per tire carrying capacity is 1,521 lbs. It is crucial to be aware of this number when having new tires put on your vehicle, because you should only use tires with an appropriate load index as per the manufacturer’s recommendation.
The final part of the sequence is the letter behind the load index: P215/65R15 95H. “H” indicates the speed rating, which is the max safe speed measured in miles per hour (mph) that the tire should be driven on for lengthy periods. In this case, “H” equals speeds up to 130 mph, but this does not mean that those speeds should be driven at all times – it is only the top speed that the tire will be able to handle over an extended duration.
Now that you are familiar with just what the sequence of numbers and letters on your tires means, you can confidently shop for tires the next time you need them. This knowledge can help you to find the correct tires and let you avoid paying more for tire aspects that you may not need.