In the past you may have been asked, “What is the size of your tire?” and you had no idea of the answer. If this has happened to you, continue reading! Maybe you knew the answer, let’s use 185/60R15 as an example. You may have been thinking “What the heck does that mean anyway?” When I first started working for the business I needed to learn a lot about these tire sizes. To save you all the embarrassment and confusion that I suffered, I am briefly going to explain in simple terms what these numbers mean and where you can find them.
Tire manufactures use a size designation that measures your tire’s dimensions in millimeters and inches with mathematics. If only we could choose between English or metric, life would be much easier! I want to refer back to our example size: 185/60R15. The first number in the sequence, 185, refers to the width of the tire from sidewall to sidewall measured in millimeters. A conversion to inches would require you to divide this number by 25.4.
Our equation: 185mm / 25.4 = 7.28 inches (width)
I find this conversion helps to make sense of the number since most of us are more familiar with inches. Moving on, the second and most important number in a tire size is a little more complicated to understand; it is a ratio. The 60 in our example is the aspect ratio of the sidewall height to the tire width (185mm). By completing the equation below you can determine the sidewall height in millimeters or inches.
Our equation: 185mm x 0.60 = 111mm (sidewall height) or 7.29in x 0.60 = 4.37 inches
This middle number is most important to Anywhere Tire Care (and most other shops) because this is how we determine our installation prices. The lower the middle number or series number, the more difficult the tire is to install. The third and final number in a tire size is probably the easiest to understand, it is the diameter of the wheel in inches. Once again, using our example our wheel diameter is 15. If you’d like to further confuse yourself or prefer metric measurements, here is how to convert your wheel size to millimeters.
Our equation: 15in x 25.4 = 381mm
If you are interested in determining the overall diameter of your tire simply add the wheel diameter and the sidewall height (x2).
15in + 4.37in +4.37in = 23.74in total diameter
When you are ready to purchase new tires you will need this information. Here is where to find it: first check your tire, the size is usually written on the sidewall. If this area is not visible, try peaking at the inside of your driver side door where the handle latches to the body. On some vehicles, Volvo’s in particular, the tire size can also be found on the inside of your gas cap. Hope you enjoyed reading and learned something knew!
Kelcy Newman
Office Manager @ Anywhere Tire Care
Anywheretirecare.com
518-810-5244
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