Wheels that don’t fit right make for a rough ride. They can also be dangerous. You don’t need fancy tools to check if your tires are correct. The answers are printed on the sidewall. It looks like a random jumble of letters and numbers. You just need to know the code.
Decoding the Sidewall Markings
Find the alphanumeric sequence on the tire’s side. The first character defines the tire class.
- P stands for passenger car tires.
- LT is for light truck tires.
- T indicates a temporary spare tire.
Next come three digits. This number shows the tire’s section width in millimeters. This is the standard international measure.
A slash follows. Then two more digits appear. These represent the aspect ratio. This is the height of the sidewall compared to the width.
After that is the letter R. It means radial construction. Finally, two digits indicate the wheel diameter in inches.
Measuring Without the Code
Sometimes you need physical dimensions. Maybe the code is worn off. Here is how to take manual measurements.
First, inflate the tire completely. Ensure it is mounted on the vehicle.
- Tread Width : Place the tape measure across the tread. Measure from the inner edge to the outer edge.
- Overall Diameter : Run the tape from one side of the tire to the other. Go straight across the center. This gives you the outside width or diameter.
- Sidewall Height : Measure vertically. Start where the tire bead meets the wheel rim. Go up to the top of the tread.
Why bother reading the code if you can measure? The code tells you the design intent. Measurements tell you what is actually there. They are not always the same. Factory specs vary from real-world wear.
Which method do you trust more? The printed number or the physical tape?
