What Do the Numbers on a Tire Mean?
We rarely buy new cars, but we buy new tires all the time.
According to the United States Department of Transportation, the average car on American roads today is more than 12 years old. The average American drives about 13,500 miles a year, and most new tires are good for between 40,000 and 70,000 miles.
That means that most cars go through up to five sets of tires in their lifespan, even if their drivers somehow manage never to pop a tire in a nasty pothole. Some of us routinely go through tires faster than that, thanks to bad luck or a more aggressive driving style.
If you’re going to own a car, you need to know a few things about tires.
Thankfully, most of what you need to know about a set of tires is written on the sidewall of the tire itself. The sidewall of a tire explains everything from its size to its mileage rating to the type of weather it can handle.
Much of it is written in code, so you’ll need some guidance to understand it all. This guide should provide an easy way to decode the markings and learn how to read tire numbers.
Tire Manufacturers
The largest font on the sidewall of a tire is usually reserved for advertising who made it. Mega brands like Goodyear, Michelin, and Yokohama make most of the tires for sale in the U.S. today.
Some smaller manufacturers operate in niche categories. For example, consider Gladiator, makers of off-road tires, and Pirelli, best known for ultra-high-performance tires found on some high-end sports cars.
Model Name
Tires have model names just like cars do. The model name will usually be listed after the manufacturer name, as in Michelin Pilot Sport or Yokohama Advan Apex.
How to Read Tire Size
A code on the sidewall explains many details about your tires. The code follows a pattern.
Let’s break down this example:
P 225/45 R 18 95 H M+S
Tire Type: (P)
The first letter of the code explains the type of tire. The types include Passenger (P), Light Truck (LT), Special Trailer (ST), Commercial (C), and Temporary (T), used only for spare tires, not intended for regular use.
Width: (225)
The second portion of the code is the tire’s width, given in millimeters. It’s best to replace your tires with new tires of the same width since your car’s manufacturer tuned the rest of the car to best operate with tires of that width. While it is possible to mount tires of a different width than the ones your car came with, doing so safely requires additional adjustments that can get costly.
Height to Width Ratio: (45)
The third item in the code is the ratio of the tire’s height to its width. In this example, the height is 45% of the tire’s width. Mounting tires of a different height ratio can change the way your car’s suspension behaves. This is rarely worthwhile in daily drivers, but off-road enthusiasts can find the added ground clearance worth the adjustments.
Construction Type: (R)
The next item in the code specifies how the tire is constructed. Almost all tires available today are built with radial construction. This means cords of rubber were laid out radially, 90 degrees from the direction of travel. Bias-ply tires (where the cords are crisscrossed over one another) are sometimes used on trailers.
Diameter: (18)
This part in the code explains the diameter of the wheel the tire is mounted on in inches. It’s not possible to mount tires of a different diameter without also buying new wheels.
Load Index: (95)
The sixth number in the code lists the tire’s load index. This is a measure engineers use to show the maximum amount of weight the tire can support when fully inflated. Tires sold on passenger cars typically range from 70 to 126.
Tires with a load index of 95 can hold up to 1,521 pounds. Those with an index of 126 can carry 3,748 pounds.
Speed Rating: (H)
According to the manufacturer, this seventh item in the code is the tire’s speed rating — the maximum speed the tire can safely travel. A speed rating of H means this tire can travel up to 130 mph. It is important to note that speed rating is tested on a healthy tire. A tire with a puncture (even if it has been professionally repaired), a weak spot from rubbing against a curb, or a tire that is not properly inflated may not be safely driven at its certified speed.
Common Speed Ratings
Using code to maximum speed, we break down how to read the ratings for common speed using the letter code and the maximum speed.
- L: 75 mph
- M: 81 mph
- N: 87 mph
- P: 93 mph
- Q: 99 mph
- R: 106 mph
- S: 112 mph
- T: 118 mph
- U: 124 mph
- H: 130 mph
- V: 149 mph
Severe Weather Rating: (M+S)
Some, but not all, tires will show an eighth and final item in the code. This is a severe weather rating. It may read M+S, meaning mud and snow. Some tires also have a snowflake symbol in this location. If your tires do not have the eighth item in the code, they are three-season tires not intended for use in heavy winters.
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Treadwear, Traction, and Temperature
Typically in smaller font, often close to the tire’s inner edge, you’ll find a rating for treadwear, traction, and temperature grades.
Treadwear
Treadwear is given as a three-digit comparative rating, established by National Highway Traffic Safety Administration regulations. Manufacturers test how quickly their tires wear on a test track compared to a standardized test tire.
A rating of 100 means that the tire lasts as long as the test tire. A rating of 200 means it lasts twice as long. However, this rating system is not particularly useful to you as a buyer. Manufacturers will generally advertise a tire as being built to drive a set number of miles, which is a more useful measure.
Traction
Traction grades reflect the tire’s ability to stop on wet pavement when tested on concrete and asphalt surfaces. The government-mandated traction test does not take into account anti-lock braking systems (ABS). ABS is legally required on all new cars in the U.S., but older cars may not have it. It can significantly improve stopping distance on wet pavement.
In order from best to worst, Traction grades are AA, A, B, and C.
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Temperature
Tires heat up as you drive. An overheated tire can fail and rip apart, which can quickly turn into a safety hazard. A tire’s temperature rating measures its resistance to overheating at high speed.
Temperature Ratings:
Code/Maximum Speed:
A: 115+ mph
B: 110-115 mph
C: 85-100 mph
Maximum Allowable Inflation
Usually located on the inner rim of the tire, in fairly small font, is the maximum inflation pressure. It is unsafe to inflate the tire beyond this point. However, it’s best not to use this as a guide when inflating your tires. Tires perform differently when carrying different weights, so your car’s weight affects the proper inflation level.
You’ll find an inflation chart on the driver’s side doorsill of your car. This shows the proper inflation level for best performance, which is usually lower than the maximum rating listed on the tire.
Inflate your tires to the pressure listed on the car or in your owner’s manual, not on the tires.
Maximum Load Rating
You will find the maximum amount of weight the tires can support also listed on the inner rim in small font. While you should never exceed this weight, it is only one factor in how much weight your vehicle can carry. A vehicle’s payload capacity is also affected by its suspension, its frame, and its own weight.
See our payload capacity guide for more information.
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U.S. DOT ID Number
Each tire model gets assigned an identification number by the U.S. Department of Transportation. This is listed in small print on the inside rim of the tire. DOT Identification numbers are generally not something consumers need to know.
Even when the government orders a safety recall for a particular tire model, they will do so by referring to the manufacturer and model.
RELATED STORIES: https://www.kbb.com/latest-recalls/gm-tire-recall/
Manufacture Date
The date the tire was manufactured is listed after the DOT ID number. However, it is not presented in the usual fashion. Rather, the first two digits specify which week of the year the tire was made, and the last two digits specify the year.
A tire with a date code of 1421, for instance, was manufactured in the 14th week of 2021 or between March 28 and April 3.
Other Text and Warnings
Tires are not required to carry any additional information. Tire manufacturers occasionally write warnings against common errors on some of their tires, such as “do not install on 16.5-inch wheels,” but these are usually aimed at the technicians installing them.
When You Should Replace Your Tires
Tires must be replaced when they are damaged or when their tread has worn to an unsafe level. For more detail, read when to replace your tires.
