You're driving down the road, when suddenly, the car swerves. You regain control but can't ignore that thump-thump-thump noise, so you pull over to inspect your wheels. Three of the tires look fine, but the fourth isn't exactly round anymore. You're stuck on the side of the road with a dreaded flat tire. What can you do now?
You will need an inflated spare tire. Most cars are equipped with full-size spare tires or compact tires (also called donuts) pre-mounted on a wheel that fits your car. You will also need a car jack (scissor, crank or hydraulic bottle) that fits your vehicle; if you purchase one aftermarket, make sure it will hold the maximum weight of your car. You will also need a lug wrench or tire iron -- a 4-way tire iron offers different size sockets and may allow you more leverage. Manual air pumps or portable battery operated air compressors are useful if your spare is not fully inflated, but they not as effective as the compressors found in service stations. If you have locking lug nuts on your wheels, then you will need the "key." It usually resembles an inside socket and might be in your glove compartment.
Make sure that you can pull your car off to the side on level ground and safely out of traffic. Chock the wheels (front and back) with wood, heavy rocks or commercial wheel blocks to prevent the car rolling off the jack. Roll the spare tire to the site where you will be working. Remove the hubcap and/or wheel cap and partially loosen the lug nuts using the tire iron. Place the jack under the metal frame in a secure spot, and then pump the jack slowly and firmly until the tire to be replaced is off the ground and high enough for a fully inflated tire.
If the car starts to slip at any point, lower it back to the ground (so long as you can do so safely) and reposition the jack. Finish removing the lug nuts and then remove the tire. Replace the flat with the spare tire making sure the wheel aligns with the lug nuts. Hand-tighten the lug nuts and lower the car to the ground. Make sure the lug nuts are tightened using the lug wrench before driving the vehicle. Nonmatching spare or donut tires should be replaced as soon as possible to ensure proper road traction and full use of ABS systems and gas mileage.
Sometimes if the tire has a minor puncture and you are just a few miles from help, you can use a canned aerosol tire fix. Sprayed through the tire valve, this will give you a few miles grace to reach a garage or tire shop where you can have the tire permanently plugged or replaced. Tire sealants are sold under a variety of names and stocked by many automotive stores like Fix-a-Flat, Slime Tube Sealant and Quick Spair. This canned tire sealant is not a permanent fix. The sealant is sprayed into the tire in liquid form where it expands to temporarily plug a hole and fill the tire with enough pressure to drive a few (non-highway speed) miles; it is a great item to have in any roadside emergency kit.
When doing any emergency road repairs, safety comes first. Make sure that your vehicle is clear of the path of traffic and visible to oncoming cars. If the traffic is too heavy and too fast, use your cell or roadside emergency phone to call for a tow truck.
Keeping safety and preparedness in mind, make sure you have a reliable emergency roadside kit in your car that includes the tools you'll need for quick fixes along the way (e.g., canned tire inflator, flashlight, tire iron, etc.)
Check the pressure of all tires, including the spare, at least once a month and before any long road trips. Check the tread for uneven or irregular wear and cuts and bruises along the sidewalls. Check your car's alignment annually -- it will improve tire wear, fuel economy and handling. Keep tires inflated properly, and rotate them every six months. Before driving, always inspect the condition of all four tires.