The first three digits (in our case, 235) represent the Width of the tire. This measurement is always in millimeters. It represents the distance from one sidewall to the other. A wider tire generally offers more surface contact with the road, which can improve grip but may impact fuel economy.

Next comes the 65, known as the Aspect Ratio. This is perhaps the most misunderstood number on the tire. It is not a direct measurement in millimeters; rather, it is a percentage.

To find the actual height of your tire's sidewall, you calculate the percentage of the width. In this example, the sidewall height is 65% of 235 mm.

235 mm times 0.65 = 152.75 mm

A lower aspect ratio (like 40 or 50) typically means a "low profile" tire, often found on performance vehicles for better cornering, while a higher ratio (like 65 or 70) provides a taller sidewall and a more cushioned ride.

The letter R stands for Radial. This refers to the way the tire is constructed, specifically, that the ply cords run radially (at 90 degrees) to the direction of travel. This is the industry standard for almost all passenger vehicles today because it offers better heat dissipation and a smoother ride.

The 17 is the Rim Diameter. This tells you exactly what size wheel the tire is designed to fit, measured in inches. It is critical never to attempt to mount a tire on a rim size it wasn't built for.

Beyond the size, you will see a two- or three-digit number followed by a letter (e.g., 104V). As Sherwin emphasizes, these are the Load Index and Speed Rating, and they are arguably the most important numbers for your safety.

Load Index: This numerical code represents the maximum weight the tire can support when properly inflated. If you install a tire with a lower load index than what is specified in your Toyota Owner’s Manual, you risk tire failure under heavy loads or high speeds.

Speed Rating: The letter (such as T, H, or V) indicates the maximum speed the tire can safely maintain over time. Even if you never drive at top speeds, the speed rating also correlates to the tire's ability to handle heat and its overall maneuverability.