Tires are one of the most overlooked parts of a car. According the Rubber Manufacturers Association (RMA), only one out of 10 drivers checks his or her tire pressure correctly, compared with almost seven out of 10 who wash their cars regularly [source: RMA]. But the truth is that an under-inflated, over-inflated, worn down or misaligned tire can be extremely dangerous, particularly in hot summer weather.
Tire pressure changes with the rising temperatures -- approximately one to two PSI (pounds per square inch) for every 10-degree increase in outside air temperature [source: RMA]. Consult your owner's manual or the sidewall of your tire to see what your tire pressure should be and check it with a hand pressure gauge or just let the guys at the service shop do it for you.
An under-inflated tire bulges outward and puts undo pressure on the sidewalls of the tire. With enough heat and pressure, that tire eventually will blow. An over-inflated tire, on the other hand, makes less contact with the road and can lead to hydroplaning in wet conditions.
Use the penny trick to see if you still have enough tread on your tires. Stick a penny in the tread, and if Lincoln's head disappears, you're good [source: CBS News]. Your local service shop or specialty tire store can also check your tires for proper alignment and balance.
And don't forget about your spare! There's no point in having a spare tire if your spare is in worse condition than the rest. Make sure the spare is properly inflated and has ample tread depth.
Source: How Stuff Works.com
Besides being a safety concern, improperly inflated and misaligned tires can lower your car's fuel economy. If your tires are a total of eight pounds under-inflated -- not uncommon at all -- you'll waste up to up to a gallon of gas per month