Deciphering tyre sidewall markings
Have you seen the marks on the tyre sidewall? These are abbreviations for a lot of information. Obviously, the tyre model name is there and proper, but that's only the beginning. A series of numbers also details the load index, speed rating, tyre size, structure, and much more.
What is the significance of these markings? This information is required when it comes time to change the tyres on your wheels. When purchasing new tyres, every driver wants to ensure maximum safety and performance; understanding the sidewall marks is an excellent approach to do just that.
Follow along as our tyre expert Nels explains tyre sidewall markings:
As an example, consider the following tyre marking sequence: 225/45 R 18 95 H
"225" is the first number in the sequence. This value represents the tire's nominal width (in millimeters) from one sidewall to the other.
The next number in the sequence after the slash is "45." This is the aspect ratio of the tire, which is simply the height of the tire's profile outward from the rim expressed as a percentage of the tire's width. This figure is calculated by dividing the tire's section height by the tire's section width. Hence, if a tyre has an aspect ratio of 45, it signifies that the height of the tyre is 45% of its width.
The next letter in our tyre marks series replaces a number. This letter denotes the type of construction utilized within the tyre casing, which in this case is "R" for Radial construction. Additional abbreviations include "B" for Bias-ply and "D" for Diagonal construction.
Radial tyres are the most prevalent type of tyre on the market today. They're named radial because the internal ply cords of the tyre are oriented radially, from one bead over to the other, at right angles to the direction of rotation.
Diameter of the rim
In our case, the value "18" denotes the diameter of the wheel rim in inches.
The load index
The load index is represented by the number after the rim diameter. In this example, "95" represents the maximum load a tyre can withstand when completely inflated. Passenger tyres have load indices ranging from 75 to 105, with each number corresponding to a different load capacity. A load index chart in your vehicle or tyre paperwork describes the carrying capability for each number. Additional details about the load index.
The speed rating is the last on our list. The speed rating is represented by letters ranging from A to Z. Each letter represents the highest speed a tyre can maintain while carrying the recommended load capacity.
In our case, "H" corresponds to a top speed of 209 kph (130 mph). Despite the fact that a tyre can operate at this pace, drivers should not exceed authorized speed restrictions. Read our speed ranking guide.
More letters and symbols may appear on the walls after this series of information.
In our case, they represent the following: Run-flat tyre with self-support
Genuine Mercedes Equipment key
Ideal for use in dirt and snow.
Meets or exceeds US Department of Transportation motor vehicle safety requirements
Year of production
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