How To Measure Tire Size

What’s a car without tires? Answer: Nothing. Indeed, a car that’s missing tires won’t go anywhere. Even Fred Flintstone knows this. Therefore, the importance of tires should never be taken for granted. Always bring a spare, make sure your tires are properly inflated, and best of all know, when they need replacement other than the fact that they’ve gone flat. When the time comes for you to replace the tires, the challenge is how to do this properly. Tires don’t come in uniform sizes and are very dependent on the type of vehicle you are driving around in. Without proper background information, you might very well end up with incorrect sizing that impacts your car performance overall. That’s why from the get go, you must know how to measure tire size.

Here are different ways to come up with the correct tire measurement.

1.    Use a measuring tool. It’s a very simple tool actually. You just need a vinyl tape measure, the loose kind used by tailors in the dressmaking shop and for your information tires are measured in millimeters so this is one of those times when you are forced to hold off on using inches as your unit of length.

2.    Begin your inspection. Start looking into the sidewall of the vehicle’s tires. The first thing you will see is the brand of the tire - Firestone, Michelin, Dunlop are some examples. Following it, you will read a series of letters and numbers that alludes to load capacity, dimensions, durability, heat resistance, and such. This is also indicative of whether the tires were made for rough/smooth terrain, regular roads, and wet/icy roads.

3.    Pay attention to the letters. You would not be remiss at all in thinking that tires are mostly measured using numbers as stated in item No.1. That is correct. However, it takes more than that. Tire sizes are also determined with letters. Here’s a breakdown for clarity:

  • P – Passenger Vehicles
  • T – Temporary Spare
  • LT – Light-Truck Metric Vehicles
  • C – Commercial
  • ST – Special Trailer Service

4.    Identify succeeding numbers. Once tire sizes are identified by the letters specifying the purpose, you will see a series of numerical data after the letter that reads something like this:

  • P255 – In this case, the numbers 255 represent the tire’s section width in the internationally-accepted millimeter unit of length.
  • P255/60 – The number 60 is your tire’s aspect ratio or the size of your tire from the rim to the tread. This is also called the sidewall height.
  • 8, 10, and 12 – These are examples of tire and wheel diameters that always have to match for your vehicle to run well. To know if you are already reading the tire and wheel diameter information in your tire, check for a letter “R” preceding it. The letter R stands for Radial construction that remains today as the most popular internal construction used in tires.

Last but not the least, it is very important to have properly inflated tires to come up with the correct results. The suggestions presented here are ideas about how you can measure the size of your vehicle tires. It’s complicated and will take some time to master but with the help of a good car mechanic, you will know how to do this if you really want to learn.


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