Tire Pressure

What is this?

Most vehicles list tire pressure requirements on one of the door posts, most often the driver's.

Tire pressure is a measure of the amount of air in a vehicle's tires, in pounds per square inch. The required service involves checking the tires' pressure with a pressure gauge, at least monthly, if not more frequently.

Should I do this service when it's recommended?

Yes. Absolutely.

Why do I have to do this?

Having the proper tire pressure is a crucial safety issue. Next to the brakes, the tires are the most important safety devices on your car. Incorrect tire pressure will compromise cornering, braking and stability. And in the worst-case scenario, improper tire pressure can lead to tire failure — and a serious accident. Incorrect tire pressure also will affect your comfort, fuel economy and tire life.

What happens if I don't do this?

If tire pressure is too high, then less of the tire touches the ground. As a consequence, your car will bounce around on the road. And when your tires are bouncing instead of firmly planted on the road, traction suffers and so do your stopping distances. You'll also feel a decrease in ride comfort. (Hint: If you notice that every tie you own has coffee on it, check your tire pressure. It may be too high.)

If tire pressure is too low, then too much of the tire's surface area touches the ground, which increases friction between the road and the tire. As a result, not only will your tires wear prematurely, but they also could overheat. Overheating can lead to tread separation — and a nasty accident. One sign of low tire pressure is if your tires squeal when cornering.

And you need to check your tire pressure even if your tires aren't leaking. Why? Because tire pressure also changes with the temperature outside. Tire pressure decreases by about 1 pound per square inch for every 10-degree drop in outside air temperature. So if you last had your tire pressure checked in July, when it was 80 degrees outside, and it's now January — and the temperature is minus 20 — your tires may be underinflated by 10 pounds, which is dangerous.

How do you determine the correct tire pressure for your car's tires?

If the specs aren't on any door post, check inside the glove compartment (pictured), under the center console cover or in the owner's manual.

A lot of people check the pressure listed on the tires themselves, but that's actually the wrong place to look. The number on the tire is the maximum allowable air pressure — not the recommendedpressure for that tire when used on your vehicle.

The recommended tire pressure is almost always lower than the maximum tire pressure. Check your owner's manual to find out where to look on your vehicle to find the recommended measurement. This number usually is indicated either on the driver's door pillar, the glove compartment door or sometimes on the gas filler door.

We recommend a high-quality digital or dial-type tire-pressure gauge like this one.

Once you know the manufacturer's recommended tire pressure, then you need an accurate tire gauge to check the tire pressure. Some tire gauges, such as the popular pencil-style gauge, are notoriously inaccurate. Analog, dial-type gauges or digital gauges tend to be fairly accurate.

And when should you check the tire pressure? You should check it when the tire is cold. That doesn't mean you need to move to International Falls, Minn., to check your tire pressure. Cold, in this sense, simply means that your tires are at air temperature. You can check tire pressure any time of the day, as long as the tires have been sitting for a few hours or haven't been driven for more than a few miles. In other words, you can drive to the gas station a few blocks away and ask them to check the pressure, but don't expect to pull off the highway after driving for an hour and expect to get an accurate reading.

When you do check your tire pressure, remember to check all four tires. Just because three of your tires are at 30 pounds doesn't mean that the fourth tire isn't nearly flat. Finally, check the spare tire at least once in a while — it would be an unpleasant surprise to find it flat when you need it. If you have a small, space-saver spare, then the pressure for that tire is probably not the same pressure as your regular tires. The correct tire pressure should be printed right on this particular type of spare.

Power-Steering Fluid

What is this?

In power rack-and-pinion steering, fluid pressurized by the pump pushes on either side of a piston mounted to the rack, helping you turn the wheels.

Simply put, power-steering fluid is the hydraulic fluid that transmits the power in power steering. Servicing it involves draining or flushing out your car's old power-steering fluid and then adding fresh power steering fluid.

Should I do this service when it's recommended?

Absolutely. The fluid is the cheapest component of your power-steering system. Changing it can help to prolong the life of other, more expensive power-steering components such as the power-steering pump and the stratospherically expensive power-steering rack.

Why do I have to do this?

Over time, the seals, O-rings and internal power-steering components will wear out. When they break apart, they contaminate the power-steering fluid, which forces the power-steering pump to work harder (having to pump little chunks instead of just fluid) and eventually break down.

What happens if I don't do this?

You'll eventually chew up your power-steering pump. It'll have to be replaced at a cost of several hundred dollars, or you'll have no power steering — and you can't easily drive a car that's equipped with power steering when the power-steering system fails. You also may damage the rack, which will require you to take out a small home-equity loan to replace.

Drive Belts

What is this?

Tiny cracks in a serpentine belt aren't necessarily bad, but the deep ones here mean it's running out of time. Because this belt was removed to replace an alternator, the mechanic replaced it with a new one to save trouble down the road.

This is the inspection or replacement of the belt(s) in your engine compartment.

Every car has a water pump, a power-steering pump and various accessories — all of which are powered by rubber drive belts. On older cars, each of these components is driven by its own belt. On most modern cars, all of these components are driven by one belt, called a serpentine belt.

Should I do this service when it's recommended?

Definitely.

Why do I have to do this?

Belts in your car don't last forever. They wear out from use and eventually crack and decay from ozone that's in the air.

What happens if I don't do this?

If your car has individual belts and one of them breaks, then you'll lose the function of whatever part that belt was powering, such as the alternator, power-steering pump or water pump. If the serpentine belt breaks, all of these parts will stop functioning. Engine damage may result from overheating.

Brakes

What is it?

Brake pads, linings and rotors are parts of your car's brake system and are housed next to each of the wheels. They push against one another to create friction, which stops the car.

The disc brake caliper (1) squeezes brake pads (2) against either side of the rotor (3). The rotor is part of the hub (4), to which the wheel attaches.

There are two kinds of brake systems: disc brakes and drum brakes. Disc brakes are the most common system in use today, and they're very much like the hand brakes on a bicycle. When you step on your car's brake pedal, the brake pads squeeze a spinning disc rotor that's attached to the wheel. The resulting friction, when applied to each of the wheels, slows the car.

The second type, drum brakes, involve brake shoes that push out against a spinning brake drum, which is attached to the wheel. This friction slows the car.

Both systems work by creating friction, so brake parts are expected to wear out. The questions then are, how worn out are they? And are they worn out enough that they need to be replaced?

That's what this service is all about checking these components for wear and other potential problems.

Should I do this service when it's recommended?

Absolutely.

Why do I have to do this?

In short, you do this service so you don't crash into a cabbage truck.

What happens if I don't do this?

If you neglect your brake pads and shoes, your brakes will ultimately fail. Even before that happens, however, you can cause damage to other, more expensive brake parts, such as rotors, drums and calipers. In other words: a stitch in time ... saves you from helping your mechanic with a boat payment later on.