Here's some quick reference to help you make your driving experience more enjoyable:

How do I know when I really need new tires?
You can't always tell by looking at the tread depth. Sometimes a tire that appears to have significant tread remaining needs to be replaced. So check the treadwear indicators -- bald spots that appear at various intervals on the tread. If you see them in three or more places, you need a new tire.
Also, you need a new tire if:

Why can't I just use water in my radiator?
You vehicle's coolant system is set for the proper coolant mix. With plain water, or the wrong mix, your engine could get too hot, but you wouldn't get the "overheated" warning. Your engine could be badly damaged and might even catch fire. Also, too much water in the mix can freeze and crack the engine, radiator, heater core, and other parts. Damage resulting from using plain water or the wrong mixture would not be covered by your warranty. See your Owner's Manual for more specific information.

A 50/50 mixture of water and the proper coolant will:

Why do I have to keep changing the oil if I'm not burning any?
Oil helps protect your vehicle's engine from premature wear by suspending moisture, abrasive dirt, and contaminants until they're broken down by detergents and trapped by the oil filter. But over time, even the best oil loses its ability to do the job. That's why regular oil changes are so important. Even if you don't drive many miles, stop-and-go driving and repeated short trips can increase your vehicle's need for an oil change.

What's the best grade of oil?
Oils recommended for your GM vehicle (gasoline engine only) can be identified by looking for the "starburst" symbol, indicating that the oil has been certified by the American Petroleum Institute (API). Do not use any oil that does not carry this symbol. Check your Owner's Manual for the proper viscosity grade. Diesel engines have a different API symbol.

What is octane?
The octane number or octane rating is a measure of the anti-knock properties of gasoline -- a higher number indicates a smaller likelihood of knocking. Using a higher-octane fuel than your Owner's Manual calls for is a waste of money. It doesn't produce more power, performance, or fuel savings. Follow the Owner's Manual recommendations regarding fuel octane for your vehicle. The only time that higher octane fuels might be necessary is if your vehicle suffers audible engine knock at highway speeds.

I don't smoke, so what's the film buildup on the inside of my windshield?
The film buildup occurs primarily as a result of harmless agents called plasticizers, which are released from the plastic interior parts and condense on glass surfaces. You can clean them off with GM Glass Cleaner, part number 1050427.

When I'm waiting in my car with the engine running, how long of a wait justifies turning the engine off?
Restarting your vehicle's engine uses about as much gas as 30 seconds worth of idling. Therefore, shutting off your vehicle's engine when you'll be at a standstill for more than half a minute will improve your gas mileage and put fewer emissions in the air.

How come they never lubricate the lug nuts on my wheels? Wouldn't that make them easier to take off when I change a tire?
Lug nuts or studs should never be lubricated. While it may make them easier to remove, they could come off while you're driving. If you can't remove them with the equipment in your vehicle, call the GM Roadside Assistance line provided in your Owner's Manual.

What good is tire rotation?
Rotating your tires helps them last longer and helps ensure safer driving by evening out tire wear. Not rotating tires may cause the tires on the drive wheels to wear out and have to be replaced prematurely. Tires on the drive wheels tend to get more wear than the other tires. Your vehicle Owner's Manual will tell you which rotational pattern to follow.

What's wheel balancing?
When a wheel is unbalanced, there is an unequal distribution of weight around the rim of the wheel and tire assembly. The tire may seem round and true when rotated slowly, but on the road centrifugal force acts on the heaviest part of the tire, making it wobble or vibrate (like an out-of-balance ceiling fan). This can cause flat spots on the tire treads and is damaging to ball joints, bearings, steering, and shock absorbers. With special equipment, technicians can measure a tire and wheel assembly, then add special wheel weights to restore balance. Hitting potholes and normal vehicle wear-and-tear can cause unbalanced wheels. Uneven tire wear can indicate unbalanced wheels, so it's wise to check and rotate your vehicle's tires regularly.

What's wheel alignment?
Aligning a vehicle's wheels involves setting the front and/or rear suspension and steering angles to manufacturer's specifications. Vehicle suspensions are designed to be at certain dimensions and angles when the vehicle is level and loaded to designated conditions. These settings affect the way the vehicle rides and handles when in motion. When you have a front-wheel-drive vehicle with independent rear suspension, four-wheel alignment is usually needed. In addition to aligning the front wheels, many other factors (like the suspension, steering, tires, shock absorbers, and passenger and cargo loading) must be taken into account. Because the technology in today's vehicles tends to mask the need for an alignment, drivers tend to overlook this need. Uneven tire wear, or even steering pulls or leads can indicate the need to have the wheel alignment checked or adjusted.

What's fuel injection?
Fuel injection delivers the right amount of fuel to the engine cylinders to allow smooth operation under all conditions. Fuel injection is computer-controlled and is more precise than older fuel delivery systems like carburetors. Fuel injectors are told by a computer to deliver more fuel for cold starting and heavy loads like hills or accelerating. On light loads, the fuel injector can be commanded to deliver less fuel or even shut completely off when coasting downhill. Fuel injected cars typically have an electric fuel pump, an inline fuel filter, and a fuel pressure regulator in the system to deliver and precisely control all the fuel that may be demanded. Maintenance can include cleaning the fuel injectors and replacing the fuel filters in the fuel line or in the fuel tank. Use GM Fuel System Treatment, part number 12345104.

What are shock absorbers?
Shock absorbers cushion road vibration and bumps. Located in the suspension near each wheel, they are connected to the wheel and the car frame. They are filled with oil and sometimes air or nitrogen to soften the vertical jolts by dampening the up-and-down motion of the springs (which absorb the main jolts). A different kind of shock, called the McPherson Strut, takes up less room and improves handling by combining the springs and shocks into one unit. When shocks and struts are worn, they can leak oil. Shock and strut wear can cause the vehicle to bounce up and down for too long after you hit a bump and cause tire and suspension wear.

What's the difference between transmission and transaxle?
Both are terms for transmissions that transfer the power from the engine to the axles. Transmissions are found in rear-wheel-drive vehicles. A driveshaft transfers power from the transmission to a differential, which changes the direction of the power 90 degrees. The drive axles then transfer power to the rear wheels. Transaxles, which combine the transmission and differential, are found in front-wheel-drive vehicles. The differential is inside the transaxle, and the drive axles are connected through constant velocity joints (CV joints) to the wheels. Transmissions and transaxles both have fluids, which may require checking or changing during the life of the vehicle. Consult your Owner's Manual.

What are disc brakes?
Disc brakes are like the calipers on bicycle brakes -- they clamp down on part of the wheel to slow it down. In a car, when you step on the brake, hydraulic (brake fluid) pressure builds up, which causes the caliper's brake pads to push against the disc or rotor inside the wheel assembly, slowing it and stopping the vehicle. Pads and calipers should be checked during tire rotation to be sure they aren't worn and the caliper is properly lubricated and free to operate on both sides of the disc brake.

What's the most popular car color?
In North America, white has traditionally been the most popular color, because it appeals to a wide range of people and is the most common color for commercial fleet vans and trucks. Black remains a strong "power color." However, earth tones have been very popular in the last few years, especially dark green. Designers predict we'll see more earth tones -- beige, gold, coral, copper and purple -- in the future.

What are anti-lock brakes?
Anti-lock brakes are a computer control feature added to the braking system. When a car has anti-lock brakes, the driver applies firm but steady pressure to the brake pedal while the anti-lock brake system (ABS) computer rapidly and repeatedly applies and releases the brake. This helps stop a vehicle in a panic situation without lock-up, skidding and loss of steering control. Since the ABS is rapidly adjusting the braking force at each wheel when engaged, drivers may notice a vibration in the pedal or hear a noise.

What is traction control?
Some vehicles have standard or optional traction control, a feature that helps the vehicle's drive wheels maintain traction on ice, or in snow, gravel, and wet pavement. Traction is improved by adjusting the engine power alone, or by adjusting both the engine power and braking system. When a drive wheel starts to slip, the traction control system will apply a brake or reduce engine power to the slipping wheel to help keep the vehicle traveling in a straight line.