HOW TO READ A TIRE SIDEWALL

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The info printed on the tire’s side tells us a lot about it. By understanding what the tire markings mean, you can know the tire’s purpose, size, how much weight it can carry, speed limit, and more. This knowledge is super helpful when you’re out looking for new tires.

SERVICE TYPE OR SIZE DESIGNATION

Sometimes, the size info begins with a letter or letters. These letters tell us about the kind of vehicle the tire fits or the job it’s meant to do. For cars and light trucks, you might see letters like P, LT, T, C, and ST.

  • P: For Passenger Cars
  • LT: For Light Trucks
  • T: Temporary, for “space-saver” spare wheels
  • C: Commercial
  • ST: Special Trailer

Tires for passenger cars that follow the Tire and Rim Association’s rules start with P. We call these P-metric size tires.

Light Truck tires also follow these rules but start with LT. This means they are made for pickup trucks, which can carry more or tow more than cars.

*Note: In old sizing methods, LT is at the tire size’s end. These are called flotation light truck sizes, like 37×12.50R17LT.

Tires starting with T are temporary spares. You use them only for a short time to replace a flat tire until you can fix or change the damaged tire.

Though not so common, tires ending with C are for vehicles that carry heavy stuff or tow trailers. The C means these tires have a commercial tread, made for vans or trucks that need to carry big loads, like 205/75R15C.

Tire sizes with ST are a bit like those ending in C, but the difference is in how much weight they can support.

SECTION WIDTH & ASPECT RATIO

This three-digit figure tells us the tire’s width in millimeters. It’s a close match to the tire’s actual width, though not always exact.

Next comes a two-digit number. It shows the tire’s aspect ratio, which is the sidewall’s height as a percentage of the tire’s width. In simple terms, this number shows how tall the tire’s side is.

After the aspect ratio, you might see a letter, often an “R”. This “R” means the tire is built in a radial pattern. Sometimes, there’s a “D” instead, indicating a bias ply construction. Here, the layers of the tire cross diagonally.

You might also find “ZR” after the aspect ratio. The “Z” in “ZR” used to signal a tire that can go faster than others rated “V”. So, a “ZR” tire can be in the speed categories of V, W, or Y. The “R” still stands for radial construction.

Finally, the size ends with two digits. These show the diameter of the wheel or rim the tire fits.

Service Descriptions Explained

Right after the wheel or rim size on tires, you’ll often see a combination of two or three numbers followed by a letter. This is known as the service description. It tells us two key things about a tire: the load index and the speed rating. The load index shows how much weight the tire can handle, while the speed rating indicates the tire’s top speed.

Below is a list that pairs typical passenger tire load index ratings with their maximum load capacities. You can also find a tire’s maximum load capacity at its highest pressure (measured in PSI) on the tire’s sidewall.

Tires might also be labeled as light load (LL), standard load (SL), or extra load (XL), which you can spot through tire markings.

Here’s a quick look at some load index figures and their corresponding maximum load capacities (in pounds):

  • 70 carries up to 739 lbs
  • 71 up to 761 lbs
  • 72 can handle 783 lbs
  • 73 supports 805 lbs
  • … and the list goes on, reaching up to:
  • 126 which can carry a hefty 3,748 lbs

This information, especially useful for understanding how much weight your tire can safely support and how fast you can go, is always at your fingertips on the tire’s sidewall.

Light Truck Load Range

On one side, light truck tires get their identity from their load range. This stretches from the letter B all the way to F. Nowadays, you’ll mostly find light truck tires in the load ranges of C, D, and E in the market. The chart below lays out the load ranges, their corresponding ply ratings, and the max load pressure for each.

Remember, it’s crucial to never go over the maximum load limit your vehicle can handle. This info is usually found on the vehicle’s placard or in the owner’s manual. Just as critical is the need to avoid surpassing the tire’s load-carrying limits that are stamped on the tire’s sidewall. Loading a tire beyond its limit can lead to too much heat, damage inside the structure, and ultimately, tire failure.

  • Load RangePly RatingMax. Load Pressure
  • B – 4 – 35 PSI
  • C – 6 – 50 PSI
  • D – 8 – 65 PSI
  • E – 10 – 80 PSI
  • F – 12 – 95 PSI

TIRE SPEED RATINGS

This table tells us how fast tires can go. Tire speed ratings make sure tires can handle the vehicle’s highest speed. The rating isn’t about how fast you should drive, but about the tire’s top speed limit.

  • A1: 3 MPH (5 KPH)
  • A2: 6 MPH (10 KPH)
  • A3: 9 MPH (15 KPH)
  • A4: 12 MPH (20 KPH)
  • A5: 16 MPH (25 KPH)
  • A6: 19 MPH (30 KPH)
  • A7: 22 MPH (35 KPH)
  • A8: 25 MPH (40 KPH)
  • B: 31 MPH (50 KPH)
  • C: 37 MPH (60 KPH)
  • D: 40 MPH (65 KPH)
  • E: 43 MPH (70 KPH)
  • F: 50 MPH (80 KPH)
  • G: 56 MPH (90 KPH)
  • J: 62 MPH (100 KPH)
  • K: 68 MPH (110 KPH)
  • L: 75 MPH (120 KPH)
  • M: 81 MPH (130 KPH)
  • N: 87 MPH (140 KPH)
  • P: 94 MPH (150 KPH)
  • Q: 100 MPH (160 KPH)
  • R: 106 MPH (170 KPH)
  • S: 112 MPH (180 KPH)
  • T: 118 MPH (190 KPH)
  • U: 124 MPH (200 KPH)
  • H: 130 MPH (210 KPH)
  • V: 149 MPH (240 KPH)
  • Z: Over 149 MPH (Over 240 KPH)
  • W: 168 MPH (270 KPH)
  • Y: 186 MPH (300 KPH)

Speed ratings like W, (W), Y, and (Y) show higher speeds. (W) and (Y) mean the tire can go beyond 168 MPH (270 KPH) and 186 MPH (300 KPH), but not over their max.

Warning

Underinflating or overloading a tire might lead to too much heat and damage inside it. Putting in too much air can also be risky, making the tires prone to cuts, punctures, or breaks from a quick hit. Such problems can lead to the tire falling apart, like the tread or belt coming off. This could be really dangerous and cause serious injuries.

Conclusion

The article elaborates on the significance of tire markings, which are essential for identifying a tire’s specifications and suitability for various vehicles and purposes. The initial segment describes service type or size designation, explaining that letters such as P, LT, T, C, and ST indicate the tire’s intended vehicle type or use, ranging from passenger cars to light trucks and temporary spares. This section emphasizes the importance of understanding these codes for selecting appropriate tires for specific vehicles or conditions.

It further details the section width and aspect ratio, explaining how these measurements provide information about the tire’s width in millimeters and the sidewall height as a percentage of the tire’s width, respectively. The inclusion of letters like “R” and “D” signify the tire’s construction type, radial or bias ply, affecting its performance characteristics.

Lastly, tire speed ratings are explained, providing a comprehensive list of speed categories from A1 to Y, indicating the maximum speed a tire can safely handle. The article concludes with a warning against underinflation, overloading, or overinflation, as these can cause excessive heat, damage, and potentially dangerous tire failures.

In conclusion, understanding tire markings is crucial for selecting the right tire, ensuring it meets the vehicle’s requirements and operates safely under various conditions. This knowledge aids in making informed decisions when purchasing new tires, contributing to overall vehicle safety and performance.

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Lucas Liam

Hi, I'm Liam, the enthusiast behind Off Road Genius. With more than 10 years of conquering diverse terrains, my experience with Jeeps extends beyond the ordinary. I've mastered the intricate details of these off-road champions, pushing their capabilities to the limit. Through this platform, I share my profound knowledge and lessons learned from countless miles on the trail. I'm here to inspire, educate, and guide you through the thrilling world of Jeeps. So, buckle up for this adventure-filled ride!

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