For some people, one of the hardest parts of picking a winter tire is deciphering the complex symbology on the tire sidewall. 'Snowflake on a mountain'? What? Let us help you break down almost everything you'll find printed on your car's rubber.
Deciphering your tires
The tire's size
The proper pressure and max load
Look for the label
Show us what you're made of
We have your number
Wine ages well, but tires don't
They don't make it easy
Turn down the heat
That's much better
Although your tires can’t talk, they have a lot to tell you. Their sidewalls are moulded with a huge amount of information, including everything from their size to the date they were made. Not all of the information is applicable to consumers, but there is a lot you can learn from your tires, and we’ll help to decipher what’s there.
Known as the “Mountain/Snowflake” logo, this pictogram indicates this tire is intended for winter use due to its traction rating, which has to be equal to or greater than a 10 percent improvement over the industry benchmark. You will find it on winter-specific tires, and also on “all-weather” or some all-season tires, which can be used throughout the year. While the logo indicates the tire meets the minimum winter standard, that standard isn’t all that high, and the logo is not by itself a measure of the tire’s quality.
You may see “All-Season” on your tires, or “M+S” (or “MS” or “M/S”), which stands for “Mud and Snow.” Tires with this mark can be used in all seasons, since, according to industry standards, their tread is aggressive enough for moderate snow conditions without being noisy on dry pavement. Their rubber compound is also formulated so it doesn’t get too soft in hot weather, or too hard in cold weather. However, since they do cover such a wide range, they are a compromise, performance-wise. If your all-season tires also have the Mountain/Snowflake logo on them, they’re considered “all-weather,” and can be used year-round in jurisdictions that legally require winter tires, such as Quebec.
This marking is the tire’s size. Tire sizes are a mishmash of Imperial and metric measurements, with a fraction thrown in. On this one, the 255 means that the tire’s width – measured across the tread – is 255 millimetres. The 45 is the fraction, and it’s called the aspect ratio. It tells you the height of the sidewall, and in this case, it is 45 percent of the tire’s width, or approximately 115 mm tall. Tires with higher numbers (and correspondingly taller sidewalls) usually give a smoother ride, while smaller numbers and their “lower profile” sidewalls are harsher but provide sportier performance. The “R” means this is a radial tire, while the 20 is the inside diameter in inches: this tire fits on a 20-inch rim.
Some tire sizes will have a “P” in front of them, indicating they’re a P-Metric size, historically used on most domestic cars. Sizes without it are Metric (or Euro-Metric), commonly used for imports or larger vehicles. The two types differ slightly in their load capacity, so always consult your tire dealer if you’re changing from one to the other. An “LT” in front of the size indicates Light Truck, a heavier-duty tire that’s often used on minivans, SUVs and some crossovers, as well as pickup trucks.
Occasionally you will see a letter in the tire size – the “Z” beside the “R” on the tire above – that indicates its speed rating. Sometimes it’s moulded elsewhere on the tire. Speed ratings are standardized tests that measure the highest speed the tire can maintain for 10 minutes without danger or damage, and primarily has to do with the tire’s ability to dissipate heat. At the low end of the scale, an “M” tire is rated for 130 km/h, while the “Z” on this tire indicates 240 km/h or higher. Higher-performance ratings – W, Y, and (Y), for example – are primarily of importance in Europe, where some highways have stretches with no speed limits.
The top number here is the maximum inflation. This is the maximum amount of air the tire can hold, but it is not the recommended pressure. That depends on the vehicle, and since tires can go on a wide range of them, the recommended pressure is found on the vehicle, not the tire.
The tire will also be marked with its maximum load, which is the most it can safely handle. This usually isn’t an issue for most drivers, but be careful if you’re carrying a lot of cargo or towing a heavy trailer, since an overloaded tire can catastrophically fail. The tire’s load rating is primarily important when you’re buying new tires, which need to match the original equipment ratings for your vehicle’s weight. Your tire dealer will know the rating required.
This is where you need to look for the recommended pressure for your tires. You’ll usually find the label inside the driver’s door jamb, or, occasionally, inside the glovebox door or the fuel filler door. It will also be in your owner’s manual. “Cold” tire pressure means the tire pressure when checked after they’ve been sitting for several hours, or driven less than a couple of kilometres.
Even if your vehicle has a tire pressure monitoring system (TPMS), you should still check the pressure once a month. Low tire pressure will result in poorer fuel economy. TPMS warns when pressure is dangerously low, but a tire could be chewing up your fuel and still be below the system’s warning threshold.
Car tires don’t require inner tubes anymore, but since some specialty tires – such as those used for agriculture – may still use them, this tire’s tubeless construction is noted on its sidewall. “Radial” refers to the tire’s construction and differentiates from a bias-ply, which generally isn’t used for car tires anymore. Tires consist of layers, or plies, which are applied at 90 degrees to the centre line of the tread on a radial tire; and at 45 degrees and crisscrossed on a bias-ply. Radial tires don’t flex as much as bias-ply tires so they provide more control, especially at higher speeds.
The tire’s construction may be moulded into its sidewall. Tire plies, the layers that make up the tire, are made of different materials that give each ply a specific characteristic. In this tire, the materials include polyester, steel, and nylon. This information is primarily for the benefit of retailers and manufacturers.
The DOT number, for Department of Transport, is essentially the tire’s “serial number,” and most of it is for the manufacturer’s use. Currently there is no requirement for the number to be printed on both sides, so if you can’t find the number, it may be on the side that’s facing the car’s underside. The various letters and numbers identify such things as where it was made, its size, and its specific identification. There are only two reasons consumers need to worry about the DOT number: during a tire recall; and when you need to know the age of the tire (see the next slide).
The last four numbers in the DOT number indicate when the tire was made. The first two are the week, and the second two are the year, so this tire’s 1712 designation means it was made in the 17th week of 2012 — the week of April 23, 2012. Although there are no government regulations on tire age, Transport Canada recommends you don’t use tires that have been stored for more than six years, and that all tires should be replaced ten years after the date they were manufactured. Verify the date when you buy new ones to be sure they’re within the recommended limit.
Prior to 2000, only the last digit of the year was included (219 would be the 21st week of 1999, for example), so if the date is only three numbers, the tire is at least 12 years old and shouldn’t be used.
Some tires are “unidirectional,” meaning that their tread pattern is designed to work optimally in one direction only. Such tires will be indicated by an arrow that shows the direction of their rotation. Make sure the tire shop mounts these tires correctly, and when you’re rotating your tires, be sure you put them back on facing the right way.
Many tires (but not winter ones) will include the Uniform Tire Quality Grading, or UTQG rating, which provides consumers with information on the tire’s tread wear, wet traction, and temperature performance. Unfortunately, the rating system isn’t the least bit consumer-friendly, and government regulators and industry are working to come up with one that is.
The UTQG tread wear is measured against a benchmark tire that’s considered to be the 100 mark, which indicates a tread lifespan of 30,000 miles (48,280 km). This tire’s 320 rating means its tread should last more than three times as long as the benchmark tire does, although it’s not a guarantee that it will, and the information doesn’t do you much good if you don’t know the benchmark in the first place. See what we mean about not being easy to figure out?
The second part of the UTQG rating is wet traction, indicated by a letter. Here, the benchmark is the equivalent of a tire that is inflated to 24 p.s.i, loaded with 492 kilograms, put on a wet test area at 65 km/h, and dragged with the brakes locked, with its friction then measured. The “A” rating in the photo indicates the best wet traction, while “B” would be slightly less, and “C” would be the poorest traction. Kind of a no-brainer as to which one you want.
The final UTQG rating is temperature. Tires heat up with friction while you’re driving. Tire manufacturers optimize their tread patterns and rubber compounds to reduce heat build-up, which can affect the tire’s performance and shorten its lifespan. The benchmark test tire is run at specific test speeds during timed intervals, while properly inflated and not overloaded. Again, the “A” rating is the best, “B” is in the middle, and “C” has the poorest performance.
New labels are in the works that will eventually replace the UTQG ratings with something consumers can actually use. They will be affixed to the tire when they’re new and will allow buyers to compare different tires at the time of purchase. The tread wear and traction rating will carry through from the UTQG, but instead of a temperature rating, the label will indicate the tire’s fuel efficiency rating, since tires play a role in overall fuel economy. While the finished design hasn’t been finalized, this is one that’s under consideration.