Do your homework before shopping for tires

Determining your needs and “knowing the numbers” makes process less daunting

Published: March 18, 2013, 9:00 PM
Updated: August 27, 2020, 5:52 PM

Tire Sidewall Markings

Shopping for tires can be a daunting task for many consumers. The range of tire types, pricing and features can be overwhelming.

One key point to remember during your shopping process is that those four small patches where the rubber meets the road are the only connection your vehicle has with Mother Earth, so don’t gamble on what could be a life-or-death decision.

One of the most important keys when looking for replacement tires is ensuring you purchase the correct size. All those sizing numbers may seem like a maze, but if you understand what those digits mean, you’re certain to find tires specifically suited to your vehicle.

First, compare the tire size currently on your vehicle with the vehicle manufacturer’s recommend sizing – this information will be listed in the owner’s manual or on a sticker affixed to a door jamb (or both.)

This step is essential, particularly if you’re not the original owner as someone may have previously replaced the original-equipment tires with a different size.

Once you know the factory-recommended tire size, make sure you understand what all those letters and numbers mean. For example, if the coding says P195/60R17 63H M S, it means the following:

• P indicates the type of tire – in this case one for passenger cars. If, however, it says "LT," the tire is designed for light truck and some SUV applications, with higher load-carrying capacity than those designed for passenger car use.

• 195 indicates the cross-sectional width of the tire, in millimetres. The higher the number, the wider the tread.

• 60 represents the aspect ratio of the sidewall compared to the width. Again, the higher the aspect ratio, the taller the sidewall – a 40-aspect tire will have a very stiff, shallow sidewall; a 70-series tire will have a taller, more flexible sidewall. Ultra high-performance tires tend to be lower in aspect to minimize sidewall flexing under high cornering loads, but that limited flexibility tends to reduce ride comfort. A higher aspect ratio may be less sporty at speed, but its ability to flex over road imperfections will result in a more comfortable ride.

• R indicates that the tire is a radial design. The alternative is a bias-ply design, which is now outdated in passenger car applications.

• 17 is the tire’s diameter, in inches, where it mounts on the wheel rim. This number matches the size of the wheel, so if your vehicle has 17-inch rims, it requires a 17-inch diameter tire.

• 63 is the load rating or the tire’s load-carrying capacity. Don’t choose a tire with less load capacity than the recommended rating. Pickup and SUV owners often opt for passenger-car tires when buying replacements because they are usually less costly and offer a smoother ride than the original-equipment LT rubber. However, if your vehicle frequently carries a lot of cargo or hauls a heavy trailer, it’s wise to stick with a higher-capacity tire.

• H is the tire's speed rating, or its ability to dissipate the heat generated during extended runs at higher speeds. Tires are speed rated from 159.3 to 299.3 km/h, with T (189.9 km/h) and H (209.2 km/h) the most common. Tires with these ratings are well suited for vehicles that spend a lot of time running long distances on highways. However, if the bulk of your driving is around town, where heat buildup is not an issue, a tire with an S rating (180.2 km/h) would be fine – and it will be less costly.

• M S indicates the tread is designed for all-weather use (not to be confused with a winter tire, which uses a mountain/snowflake marking; see below). In most cases, this tread design is a compromise, with less than optimum traction on dry roads, wet surfaces or on snow and ice. It delivers a moderate level of traction regardless of the elements, but won’t match the traction capabilities of tires designed for specific conditions.

If you live where cold, winter conditions are a fact of life, experts strongly recommend fitting your vehicle with winter tires on all four wheels for the duration of that season. If you happen to reside in an area where conditions are above freezing year round, then a touring or "summer" tire will offer better traction and wear characteristics than an all-season design. Similarly, if high performance is your preference, switching to a tire specifically designed for that application will result in superior handling.

Once you know the proper size of tire your vehicle requires, decide your specific needs. Will the bulk of your driving be on highways or on urban streets with an occasional out-of-town jaunt? Is maximum handling a priority, or do you prefer a higher level of ride comfort? How important are factors such as fuel economy, tread wear, tire noise and load –carrying capacity. These all impact the cost of the tires you select. Once you’ve determined your preferences, it’s time to go shopping.