Buying new tires can seem like an overwhelming challenge. What is the best tire? Can I save some money? Will they work on my vehicle? How long will they last? Fortunately, the staff at most tire shops are well versed in proper tire selection. But there may be a concern that the tire shop is promoting one tire rather than selecting the best for your application. Here is a quick primer on tire terminology that you should know before you go shopping:
First, you need to know the rim (wheel) diameter. This is measured across the rim at the point where the tire seals on the bead lip. It can also be found cast or stamped into the rim and moulded onto the tire. Fifteen-inch wheels and tires have been the most common size for several years, but many cars and trucks come with much larger diameter wheels now. Seventeen-inch diameter has become very common even extending to use in economy cars, while performance cars and trucks may have 18, 19 or 20-inch wheel diameters. If you are also purchasing new wheels for your vehicle, you may hear about plus one or plus two sizing. This refers to using a wheel that is one or two inches larger in diameter than the original wheel on your vehicle. Tires selected to fit these wheels will have a lower sidewall height so the overall diameter of the replacement tire remains the same as the original tire. Larger wheels can add to the attractiveness of your vehicle but there is a drawback. When manufacturers fit larger diameter wheels to a vehicle, it is often to accommodate bigger brakes for increased stopping power. Unfortunately, installing bigger brakes is not necessarily an easy or cheap option on most vehicles so it is seldom done on used vehicles. Just installing bigger diameter wheels and tires does place more mass further out on the rolling diameter of the wheel and this makes more work for the brakes, so stopping distances can actually increase. Next, you need to determine the width of tire you need. Width is measured in millimeters across the face of the tread. Wider tires provide more traction than narrower tires, but a narrow tire gets better fuel economy. Using a tire wider can create interference with mechanical parts of the vehicle, so usually you are limited to a tire size similar to the original tire on your vehicle. The final tire size to consider is the aspect ratio. This is the ratio of the height of the tire sidewall in relation to the width of the tire. An aspect ratio of 70 has a sidewall 70% of the tire width and indicates a high sidewall. An aspect ratio of 35 represents a low sidewall, which makes the tire look like a rubber band wrapped around the wheel. Different aspect ratios will change the overall diameter of the tire as the sidewall height is changed. Many cars now use a tire with an aspect ratio of 60, 55 or 50. All this information is all moulded into the tire. For example a P205/55R16 on the tire tells us it is P for passenger vehicle. If the tire reads LT, it indicates Light Truck, which is a stiffer and stronger tire for carrying higher loads, but doesn't ride as smoothly. The 205 is the width of the tire and the 55 is the aspect ratio. The letter R indicates it is a Radial tire construction, which refers to the direction of chords in the tire casing laterally across the tire. Finally, the 16 means this tire uses a 16-inch diameter wheel. Other information on the tire helps us select replacements. After the tire size, you may see a number and letter such as 89 H. The number refers to the tire load carrying capacity and the letter is the maximum safe speed for that tire (not the car!) An H rated tire is rated safe to 210 km/h and a T-rated tire is good to 190 km/h. S is the lowest rating and it is rated at 180 km/h. Finally, you will find the Uniform Tire Quality Grading System or UTQG rating. Treadwear, traction and temperature are all rated. A treadwear of 100 is baseline and higher numbers indicate better treadwear. This allows you to compare different tires. Traction and temperature are rated A, B or C with A being the best. Selecting the correct tire is still difficult, but knowing the preliminary information makes choosing easier. [Non-text portions of this message have been removed]
