Axle: the long metal rod that the wheel revolves around.

Camber: as you look at the wheel from the front, camber is the angle between a vertical line, and a line drawn through the center of the tire.

Caster: as you look at the wheel from the side, caster is the angle between a vertical line and a line drawn through the center of the steering axis .

Toe: as you look at the wheels from above, toe is the angle between a line through the center of the vehicle, and lines drawn through the centers of the tires .

Valve stem: a flexible rubber finger with metal threads on the end, that sticks out from the wheel rim. It's the point where you add or release air from the tire.

PSI: Pounds per Square Inch is a standard way to measure air pressure in many instances, including tire pressure.

Front-wheel drive: a vehicle that is propelled by the front wheels, which are driven by the engine. The rear wheels roll behind passively.

2torial #0518: Learn2 Understand Tire Care (Continued) Understand tire balancing, wheel alignment and tire rotation   There are three important services that an auto repair shop can do for your auto: balance the tires, align the wheels, and rotate the tires. The first two don't need attention that often; tire rotation needs to be done little more frequently. Balancing: No matter how well a tire is made, it's probably going to need a little help to spin correctly--i.e., without wobbling. Generally a mechanic does this by attaching small weights to the wheel rim; this offsets any irregularities in tire or rim construction. Balancing can be done with the wheel on or off the vehicle, but most times it's taken off.   When you first buy a tire and have it mounted, it should be balanced as well. As the years go by, and the tire wears down, it may need to be balanced again. A noticeable vibration in the vehicle is a good indication that a tire needs balancing (or something else is wrong--find out now!). Wheel Alignment: Picture a hoop around your waist, and imagine that it's a wheel and tire combo on an axle. If you can imagine the different ways that a hoop could shift position around your waist-- forwards, backwards and side-to-side--then you have an idea of how a wheel and tire can shift around on the end of your axle. Alignment makes sure that the wheels and tires are in the correct position in relation to your vehicle, and each other. This should be done when tires are bought and mounted on the vehicle. Camber, Caster and Toe are what need to be adjusted here. These terms are in Keywords if you're curious, but they're not essential for you to know. Just make sure the mechanic knows!) An auto manufacturer will specify precise reset values that the mechanic can look up and use to set your wheels up correctly. Due to better design and manufacturing, some vehicles stay in alignment better than others. But unless you're four-wheelin' on dirt roads, your vehicle will need to be aligned only once or twice a year. How do you know if the vehicle is out of alignment? Keep an eye on your tire tread: if the tread is wearing unevenly, take the vehicle in before the tire is seriously damaged. Another clue: while you're steering straight ahead, the vehicle has a tendency to veer to one side or the other. This may also be fixed with alignment work. In any case, there are generally two kinds of alignment offered: regular, and four-wheel or thrust-angle. If you have a vehicle with fully independent suspension, you'll need to spend the extra money to have all four wheels aligned. It's also a good idea to have four-wheel alignment on all front-wheel drive vehicles (see Keywords). Rotation: Tires wear at different rates on your vehicle. Depending on your make and model, some wheels power the vehicle, other wheels steer it, and some wheels are just along for the ride (loafers!). To get the longest wear from your tires, and to help them wear at the same rate, it's necessary to switch their positions every once in a while. Most tire companies recommend rotation as often as convenient, around every 6000 miles or so. Indeed, if you're counting on that 30,000-70,000 mile warranty that comes with most tires, you'll need to keep records of tire rotation to collect on it. At the least, it's a good idea to rotate your tires every 10,000 miles. In particular, front-wheel drive vehicles need regular rotation.   Tire rotation can be done a few different ways. Some auto manufacturers want the tires to go back and forth on the same side of the vehicle, while others specify a criss-cross type pattern. If you look in your owner's manual, you'll find out what the manufacturer recommends. Step 2