If you’ve ever wondered what all those numbers mean in a tire size, or how tall a tire will be when it’s mounted on a rim then this article is for you. There are many different configurations of tire sizes out there, but this article is going to focus on what is call a P-metric tire size. It’s the way most passenger and SUV tire sizes are referred to. Here is what one looks like.
Let’s look at each piece of the tire size above individually starting with the “P”. The “P” simply designates that this is indeed a P-metric tire size. The “235” is the section width of the tire in millimeters. The section width is the distance from the outermost part of the tire’s sidewall to the innermost part of the tire’s inner sidewall when mounted on a rim. Keep in mind that the section width is not the width of the tread. The “75” is called the aspect ratio. This number gives the section height, the distance from rim to top of the tread, expressed as a percentage of the section width. In this example, the section height is 75% of the section width. The letter following the aspect ratio designates the internal construction of the tire. In our example, the “R” means that this tire has an internal radial construction (as opposed to bias-ply). The number following the “R” is the diameter of the wheel that this tire will fit on. (more…)