Decoding Tire Code: Aspect Ratio, Tire Construction, and Wheel Diameter

Last week, we began a series for those who may be shopping for a new set of tires and need a little more information in determining which type of tires they need.  We began looking at the universal tire code that is found on most every vehicle tire manufactured. Last week we looked at the type of tire and section width. This week, we will get a little further into the code.

Aspect Ratio

The aspect ratio of the tire is listed as a percentage and gives the height of the tire from the bead to the top of the tread. Here the number is 55, which means the tire height is 55% of the section width of 215 millimeters. The height of this tire would be 118.25 millimeters. A lower number indicates a lower tire profile.

Tire Construction

The construction of the tire is identified by the letter following the aspect ratio. The most common designation is R, which stands for radial construction. Other, less common construction types for modern passenger cars may include D for bias ply construction and B for belted tires.

Wheel Diameter

The number following the construction code indicates the size of the wheel that the tire will fit in inches. The example tire would be designed to fit a 17-inch wheel. Tire sizes on most vehicles begin at 13-inches and go up to 18-inches.Custom package wheels can be 22-inches or even larger.

Why are Aspect Ratio, Tire Construction, and Wheel Diameter important?

Aspect ratio is an important sizing calculation in tire fitting, and should be considered with wheel diameter with the best tire and wheel combinations. Lower aspect ratio typically indicates a high performance tire, with better lateral stability. Most of the new tires you encounter will be marked R for radial construction, however if you are replacing old tires, you may see the D or B designations.

As with last week’s part of the code, it is important to select your vehicle manufacturer’s recommended specifications to assure safe and optimal tire performance. While buying a dependable, quality tire is important, it also must be developed for the best performance given the weight and design of your vehicle, so consulting a tire expert is a must.

Next week, we will wrap up decoding tire code by taking a look at Load Index, Speed Rating, and use designation.