Reading Tire Size
Updated: Oct 22, 2018
Reading tire size can get confusing for folks who are not car experts. A friend of mine once said reading the sidewall of her tires was like solving a crossword puzzle.
Since no one has time to solve puzzles when figuring out what their tire size is, we will breakdown the numbers in a simple manner.
In this post we stick to the basics of reading tire size numbers.
Type of tire
The first symbol in the tire size on the sidewall and also inside most door jams is a letter. Our example is P 215/55 R17. "P" stands for passenger (P-Metric), a USA standard. "LT" indicates the tire is for light trucks. No letter shows the tire to be Euro Metric.
The first set of numbers indicates the tire width in millimeters. This is measured sidewall to sidewall. Our example above shows a tire width of... you guessed it - 215 millimeters. No crossword skills needed!
P 215/55 R17
The next number after the slash is the aspect ratio. This is a reflection of the height of the tire's cross section in relation to its width. Our sample tire shows the number 55. This means the tire's height is 55 percent of the tire width. Larger aspect ratios mean the sidewall is taller.
Next in line is a letter. This lets the car owner know how the tire is constructed. The usual options are:
R - Radial
B - Belted bias
D - Diagonal bias
The last measurement we will look at is 17 - shown in our example tire size. Reading tire size has been easy so far right? This one is not hard to understand either. This number shows the wheel diameter that the tire is made to fit. Our tire example is made to go on a 17 inch wheel.
P 215/55 R17 93V
Not to be ignored is the load index. This is usually stamped on the sidewall alongside the main measurements listed above and in this example that's 93 and the V is the speed index. Most consumers don't pay attention to this number but truck guys may need to if they are hauling heavy loads.
One last note on reading tire size. No matter if your tires are big, small, or medium, it's crucial to check them often for damage. Be sure to rotate and balance them as well. If not you may be shopping for a new set sooner than you planned.
To fix and repair common tire air leaks the best new tire sealant solution is TireJect's Bead Sealer and Emergency Tire Sealant for automotive use.