The En-Tire Truth
Answers to the most common — and most important — questions about wheels
By:
Mike Berger
Online Rating:
   (7.5/10) How much do you really know about your wheels? Even if you think you know all the answers, read on. We’ve compiled the facts for these commonly asked questions (and frequently held misconceptions) to help you keep on truckin’ in safety. Do aluminum wheels have special needs?
You bet! In fact, most aluminum-wheel manufacturers provide specific installation and maintenance instructions for their products, and it’s vital that you follow them. For example, once you’ve installed aluminum wheels, you’ll need to retighten the lug nuts after driving 25 to 100 miles (depending on the manufacturer’s specifications). In addition, you should use only lug nuts that are specifically made for aluminum wheels — never mix and match! And exercise care when working with aluminum wheels, as you can scratch or ding the metal. Is a repaired tire safe to use?
Small punctures that are confined to the tread can often be repaired using industry-approved methods that are applied from inside the tire. When done by a professional, these repairs are quite safe and can often keep a good tire on the road for many more miles. But if the puncture is larger than 1/4 in. or extends into the sidewall, you’ll have to replace the tire. What is wheel balancing?
Tire-and-wheel assemblies can be balanced in two ways — statically and dynamically. In static (up-and-down) balancing, the assembly is mounted on a freely moving spindle. If one point consistently pulls to the bottom after rotation, the assembly reveals a heavy spot, and weights are placed opposite that spot to counterbalance it. In contrast, dynamic (two-plane) balancing reveals whether a tire is not only unbalanced up and down but whether one side of an assembly is heavier than the other. Tires and wheels should be balanced when new tires are mounted for the first time, when a tire and wheel are put in another position on the car or any time a tire and wheel is disassembled. In addition, you need to check tire balance at the first sign of vibration or unusual tread wear. Though these problems may be caused by misalignment or other mechanical issues, only a professional diagnosis will reveal the true cause. What do the numbers on tires’ sidewalls mean?
The first number is the tire width in millimeters from sidewall to sidewall. The number after the slash is the aspect ratio of the tire height compared with the tire width: In this case, the height is about 65 percent of the width. The next letter, either “R” or “B,” indicates tire construction: “R” means radial; “B” means bias ply. The next two digits show the wheel diameter — in this case, 16 in. Following a space will be two or three digits that describe load index, a range that indicates how much weight the tire is certified to carry at maximum inflation pressure — in this example, “98” indicates a maximum load of 1,653 pounds. The next letter (H or Q through Z) represents the speed rating — in our example, the “T” means that the tire is rated up to 118 mph. (Speed-rating and load-rating charts are available on most tire manufacturers’ Web sites.) Finally, some tire codes may include one extra designation: “M+S,” meaning the tire is rated for mud and snow. Is an impact wrench safe for lug nuts?
You can use an impact wrench to loosen lug nuts, but never use one to reinstall them (unless you’re using a torque-limiting wrench or sockets) because you’ll risk overtightening, which can lead to broken studs, warped brake drums or rotors and even cracked wheels. Instead, use a torque wrench, and evenly tighten the nuts in a crisscross pattern to the values specified by the vehicle’s manufacturer. How can I tell how old my tires are?
Every tire has a Department of Transportation (DOT) number imprinted on its sidewalls that begins with the letters “DOT” and may contain 12 additional numbers and letters. Before the year 2000, the last three digits of a DOT number represented the week (two digits) and the year (one digit) of production. So if the last three digits are 279, the tire was produced in the 27th week of 1999. Tires produced after Jan. 1, 2000, have a four-digit date code at the end of the DOT number. The first two digits represent the week of production and the last 2 digits represent the year of production. So 1806 would indicate that the tire was produced in the 18th week of the year 2006. Where can I find the proper inflation values for my tires?
Besides being listed in your vehicle’s owner’s manual, tire pressures are printed on a decal found on the doorpost, in the glove compartment or on the trunk lid. Is filling tires with nitrogen a good idea?
In theory, filling tires with 95 percent (or higher) nitrogen lessens corrosion and results in longer tire life. Nitrogen is also denser than oxygen, meaning that it bleeds out of a tire at a slower rate than regular air, resulting in less need to “top off” tire pressure. And because nitrogen is inert, it won’t react to temperature changes the way regular air does. Some shops offer nitrogen for free or for a nominal fee; others charge as much as $30 to fill four tires with nitrogen. If the shop doesn’t properly maintain its nitrogen generator’s filter, the generator will pump regular air instead of nitrogen, so you may not get what you’re paying for. Tire manufacturers insist that because regular air is 78 percent nitrogen, the benefit of a higher nitrogen content is negligible. If you can get nitrogen for free, you won’t hurt anything by using it, and you may see a slight increase in performance and handling. But if you have to pay for it, you may be better off investing your money elsewhere. |