Deciphering Tire Sidewall Codes

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What Do Tire Numbers and Letters Mean: The Basis

Ever wonder what the letters and numbers on the side of a tire represent? Although the alpha-numeric sequences may seem as like an alien coding system, it can be fairly easy to decipher. The alpha-numeric labels note the tire size, when it was manufactured, speed-rating, load and tire pressure markings, construction type, special weather ratings and the Original Equipment (OE) information.


We previously mentioned the importance of the OE information in our last blog, “How to Shop for New Tires.” When ordering tires from a local dealership or tire shop you will need to provide the OE information to ensure you are getting the correct tires for your vehicle.  The Performance Auto Group has 16 dealership locations that are conveniently located throughout Nebraska and the Kansas City area.

For more detailed information on side tire codes, continue reading Part II of this blog.


What Do Tire Numbers and Letters Mean: The Details

This section should help explain the main components of side tire coding for both car enthusiasts and those with basic tire knowledge. Collecting information prior to purchasing a new set of tires is a necessary first step.


The consumer needs to know what they are looking for in order to determine the type of tires that would best match their vehicle’s frame and performance. However, it is always recommended to double check with your local dealership before making any purchases or alterations to any vehicle.


How to Decode a Tire’s Sidewall

To determine the size, find a tire code that looks similar to this: 225/40R18. The three-digit number preceding the virgule (more commonly referred to as a slash), represents the tire’s width in millimeters. The rest of the code is an aspect ratio of the sidewall height divided by the width; the letter describes the construction of the tire, while the last two numbers represent the wheel’s diameter in inches.


As previously mentioned, the OE and tire compound/construction vary from each manufacturer but can determine for which vehicle that tire was specifically produced. For example, “M0” corresponds to a Mercedes-Benz model. Coordinating the recommended OE with the correct vehicle allow for better vehicle performance and uneven wear and tear. This tire code varies for each brand and model, so call a local dealership to compare the OE code with the vehicle’s make and model to confirm which tires are recommended for that vehicle.


There is also a code that defines the service description and speed-rating. This code will look similar to “93W.”  It defines the tire’s capabilities. The two-to-three digit number stands for the tire’s load rating. A higher number means the more weight the product can withstand. Followed by a corresponding letter, this letter determines the speed-rating (the highest suggested speed) and is marked from low to high as the following:

L (75 mph), S (112 mph, suggested for most vehicles) and Z (149 mph). More recently, manufacturers have produced a W (168 mph) and Y speed-rating tire. The “Y” rating indicates the tire can bear up to speeds of 186 mph.


Finally, special weather ratings may be presented as a pictogram or several variations of the letters “M” and “S” which stand for mud and snow and is correlated with the tire tread. A pictogram that presents a snowflake within a mountain indicates that the tire meets U.S. Rubber Manufacturing Association standards for “packed-snow-traction” requirements.


For further information for help deciphering side tire coding, refer to Car and Driver’s article, “The Rosetta of Rubber: How to Read a Tire Sidewall,” or by contacting any of Performance Automotive Group’s locations.  We encourage you to have the tred of your tires checked periodically, and wish you continued safe driving!

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