Wheels & Tires Articles

Article / Updated 05-31-2021

When shopping for tires, you need to know what the numbers and letters on your sidewall mean in order to select the appropriate replacement tire. Tires usually follow a pattern can be illustrated by dissecting "Bridgestone Potenza RE040 205/50VR15 85V" like an earthworm in formaldehyde: Brand: Bridgestone. This is the company that manufactured the tire. Series: Potenza. Tire manufacturers often create a series of tires with somewhat similar handling and performance characteristics. For example, Bridgestone uses the Potenza name on many tires that may appeal to drivers who want a performance tire, and the Turanza name on many tires that are intended for less aggressive driving (or drivers with a less aggressive self-image). Model: RE040. This is a pretty specific identification of the general performance characteristics of this tire, regardless of its size. Tires in the Potenza series vary greatly in performance, but tires of the RE040 model have virtually identical construction, tread compound, design, and ride Width: 205. This number is the width of the tire in millimeters. This is the most important number to describe a tire's contact patch. For example, a 215-width, 17-inch tire may look great, but all things being equal, a 245-width, 15-inch tire will out-corner it every time, because the contact patch is wider. Aspect ratio: 50. This is the height of the sidewall from the rim to the tread, expressed as a percentageof the tread width. For example, if the tire is 205 mm wide, and its aspect ratio is 50, then the sidewall is about 102.5 mm tall (50 percent of 205 mm). Sidewall height is important for a number of reasons: As you move up to larger wheels, or down to smaller ones, a corresponding change needs to happen in the sidewall height of the tire in order for the rolling diameter of the wheel and tire combination to be as close to stock as possible. This will ensure the accuracy of your speedometer and prevent unwanted alignment changes. The sidewall height affects the turn-in feel (the responsiveness you feel at the steering wheel) and the ride quality. Lower aspect ratio (shorter sidewall) provides better turn-in response than a higher aspect ratio, but at the expense of less break-away warning and a more jarring ride — in extreme cases, even exposing the wheels to potential bending and breaking damage from potholes and other surface irregularities. Speed rating: VR (V-rated radial). In this case, V identifies a speed rating above 149 mph. It's almost impossible to find a public road in the U.S. where you can legally drive faster than any tire's rated speed, but speed ratings are a very important safety consideration when shopping for tires for motor sports and countries that allow high speeds on public roads. Table 1 lists speed ratings. R means the tire is a radial. Virtually every new tire is a radial, unless you have a special tire for a classic car or a racing car. Table 1: Speed Rating Designations Speed Designation Maximum Speed Rating 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 W 168 mph Y 186 mph Z 149+ mph Load rating: 85V. In this case, 85 means the tire is rated for 1,135 pounds (see Table 2). Multiply this by the number of tires on the car, and you get a maximum safe loaded vehicle weight of 4,540 pounds (including people, luggage, a full tank of gas, and all the loose change under the seats). The last V repeats the V speed rating, listed in Table 1. Table 2: Load Rating Designations Load Index Load Carrying Capacity (Per Tire) Load Index Load Carrying Capacity (Per Tire) 71 761 91 1356 72 783 92 1389 73 805 93 1433 74 827 94 1477 75 853 95 1521 76 882 96 1565 77 908 97 1609 78 937 98 1653 79 963 99 1709 80 992 100 1764 81 1019 101 1819 82 1047 102 1874 83 1074 103 1929 84 1102 104 1984 85 1135 105 2039 86 1168 106 2094 87 1201 107 2149 88 1235 108 2205 89 1279 109 2271 90 1323 110 2337 If your tire isn't described by these two tables, then consult the tire manufacturer or a tire specialist, such as Tire Rack or Wheel Works, for further information.

Article / Updated 05-28-2021

You should check your tires for wear at least once a month and before and after long trips. To determine whether you need to (a) buy new tires, (b) have your wheels balanced, (c) add air into your tires, (d) have your wheels aligned, or (e) change your driving habits, simply read your tire treads for clues. Table 1 and Figure 1 show you what to look for. Table 1: How to Read Your Treads Clue Culprit Remedy Both edges worn Underinflation Add more air; check for leaks Center treads worn Overinflation Let air out to manufacturer's specifications One-sided wear Poor alignment Have wheels aligned Treads worn unevenly, with bald spots, cups, or scallops Wheel imbalance and/or poor alignment Have wheels balanced and aligned Erratically spaced bald spots Wheel imbalance or worn shocks Have wheels balanced or replace shocks Edges of front tires only worn Taking curves too fast Slow down! Saw-toothed wear pattern Poor alignment Have wheels aligned Whining, thumping, and other weird noises Poor alignment, worn tires or shocks Have wheels aligned or buy new tires or shocks Squealing on curves Poor alignment or underinflation Check wear on treads and act accordingly Figure 1: What the signs of poor tread wear mean. Underinflated tires wear out faster, create excessive heat, increase fuel consumption, and make your car harder to handle. Overinflated tires can "blow out" more easily, wear out faster, and make the car unstable and unsafe to handle. And a new set of tires on wheels that are out of alignment can wear out completely in as little as one day of hard driving! To determine what's causing problems with your tires, try the following: Look for things embedded in each tire. Do you see nails, stones, or other debris embedded in the treads? Remove them. But if you're going to remove a nail, first make sure that your spare tire is inflated and in usable shape. If you hear a hissing sound when you pull a nail, push the nail back in quickly and take the tire to be fixed. If you aren't sure whether air is escaping, put some soapy water on the hole and look for the bubbles made by escaping air. If you're still not sure whether the nail may have caused a leak, check your air pressure and then check it again the next day to see whether it's lower. Tires with leaks should be patched by a professional. If the leak persists, get a new tire. Look at the sidewalls. Check for deeply scuffed or worn areas, bulges or bubbles, small slits, or holes. Do the tires fit evenly and snugly around the wheel rims? Look at the treads. Most tires have tread-wear indicators built into them (see Figure 2). These bars of hard rubber are normally invisible but appear across treads that have been worn down to 1/16th of an inch of the surface of the tire (the legal limit in most states). If these indicators appear in two or three different places, less than 120 degrees apart on the circumference of the tire, replace the tire. Figure 2: It's time for new tires when tread-wear indicators appear. If your tires don't show these indicators and you think that they may be worn below legal tolerances, place a Lincoln penny head-down in the groove between the treads. If you can see the top of Lincoln's head, your tire probably needs to be replaced. To measure tread wear more exactly, place a thin ruler into the tread and measure the distance from the base of the tread to the surface. It should be more than 1/16 inch deep. ( Note: If your front tires are more worn than your rear ones and show abnormal wear patterns, you probably need to have your wheels aligned.) Pay attention to leaks. If you keep losing air in your tires, have your local service station check them for leaks. Sometimes an ill-fitting rim causes a leak. The garage has a machine that can fix this problem easily. If the garage can't find a leak, your rims fit properly, and you're still losing air, you probably have a faulty tire valve that's allowing air to escape. You can buy tire valves to replace the ones on your car. Look for the number molded into the base of the tire valves; then buy new ones that match it. In the process of replacing the valve, you will lose most of the air from the tire, so either plan to do this job at a gas station where you can have access to an air hose, or have a mechanic replace the valve for you.