A flat tire is something nobody wants because a flat tire will leave you stranded along side the road. When a tire loses all its air, is loses its buoyancy and the ability to support weight. Unless the tire is a special kind of tire called a "run-flat", the sidewalls are not strong enough to support the weight of the car unless there is a certain amount of air pressure inside the tire. So a puncture or leak that allows the tire to lose air will cause the tire to collapse and go flat.
Any tire, new or old, can go flat if it is punctured or leaks air. New tires have thicker treads so are more resistant to punctures than worn tires with thinner treads. But the deeper treads on a new tire can also channel sharp objects into the tire actually increasing the risk of a puncture if you drive over a nail or other sharp object.
If a tire goes flat while driving, you will hear and feel a thump, thump, thump vibration from the suspension. A flat front tire will usually cause a hard pull towards the side that has gone flat.
If a tire has gone flat while the vehicle is parked, hopefully you'll notice it before you try to drive away. If you don't, you'll immediately feel and hear the thump, thump, thump of the flat tire.
DO NOT CONTINUE DRIVING ON A FLAT TIRE!.
Driving on a flat tire will quickly ruin your tire. Without any air support inside the tire , the sidewalls of the tire will be pinched between the road and the edges of the wheel rim. Driving even a short distance (say more than 1/2 mile) may be enough to cut or destroy the tire. And if the tire comes off the rim, which a flat tire can do, you may end up damaging your wheel, too.
Common causes of flat tires include:
Leaky valve stems. There may be cracks in the rubber stem, a poor seal between the valve stem and wheel (due to corrosion or wheel damage), or an internal air leak in the valve stem because the valve is loose, faulty or jammed with dirt. Making sure the valve stem is covered with a cap will keep dirt out and help keep air in. This type of leak can be repaired by replacing the valve stem, or the valve assembly inside the valve stem.
Punctures in the tire caused by driving over sharp objects. Road debris includes junk like nails, screws, steel wire from exploded truck tires, broken glass, sharp rocks, etc. Try to avoid running over debris in the road if you see it and can react in time (which is hard to do when driving in heavy bumper-to-bumper traffic). This type of flat can be repaired by patching or plugging the tire, or replacing it if the tire is too badly damaged to be repaired.
Bead leaks between the tire and wheel. This is often due to rust or corrosion on the wheel, but can also be caused by a bent rim (hitting a curb or pothole). Air leaks here can also be caused by a damaged bead sealing surface on the tire, possibly the result of mishandling when the tire was originally mounted on the rim (not using a bead lubricant, attempting to force the bead over the rim, using the wrong mounting hardware). This type of leak may require dismounting the tire and cleaning the rim and bead surface of the tire. If the rim is bent or damaged, the wheel should be replaced. If the bead surface on the tire is damaged, the tire will have to be replaced.
Wheel air leaks. Aluminum alloy wheels can be porous and slowly seep air over time. Adding a sealer to the tire will often cure this type of leak. Or, the tire can be dismounted from the wheel so the inside of the rim can be painted or coated with sealer.
Somebody intentionally let the air out of your tire, either as a prank or to send you a message. No repairs are needed for this other than to reinflate the tire with air (use a pump, portable tank or aerosol can of tire inflator/sealer). Be careful where you park your vehicle next time!
Slow down and pull over to the side of the road as soon as it is safe to do so. DO NOT stop in the middle of the road, especially if you are on a busy highway or expressway. That's a good way to get rear-ended or killed!
Pull off on the RIGHT shoulder of the road, and try to get your vehicle as far OFF the highway as possible. This will hopefully reduce the risk of someone running into your parked vehicle. It will also leave some room if a tire on the left side of your vehicle needs to be changed.
Turn on your hazard flashers so other drivers will see you. Raising the hood is also a good idea as this is a universal signal for help.
If it is night or visibility is poor, and you have a safety flare, reflective triangle or portable warning light in your trunk, place one of these safety warning devices some distance behind your vehicle to alert oncoming drivers.
You now have to decide whether to change the flat tire yourself, or to call for assistance. If you have never changed a flat tire, or you lack the physical ability to do so, or your vehicle has no jack or spare tire, the choice has already been made for you. You will have to call for help on your cell phone, or wait for help to arrive. In some areas, there may be call boxes placed at intervals along expressways that a stranded motorist can use to call for help. If you don't see any call boxes and don't have a cell phone, you'll have to wait for a cop to drive by, or a motorist assistance truck to come by, or a Good Samaritan to stop and offer assistance. BE CAREFUL because you don't always know the motives of a person who may be offering to help you. Most people are good, honest people. But some are not.
If it is safe to do so, you should get out of your vehicle and stand back some distance from the highway until help arrives. How many cop shows have you seen where some idiot plows into the back of a vehicle that is stopped along side the road? It happens all too often.
If your stranded in a "bad" neighborhood, you might be safer waiting inside your vehicle with your doors locked.
WARNING!: Every year dozens of motorists and Good Samaritans are killed attempting to change flat tires along busy roads. The risk is greatest when changing a tire on the LEFT side of the vehicle nearest the roadway. To minimize the risk of being hit while changing a tire on the left side, your vehicle should be pulled over as far to the RIGHT as possible to put more distance between you and passing traffic. Placing safety flares, triangles or lights some distance behind your vehicle will also help alert traffic. If someone has stopped to help you, the second vehicle should be parked some distance BEHIND your vehicle to serve as a barrier. Leave at least four car lengths distance between the vehicles so if their vehicle is rear-ended and pushed forward, nobody will be crushed between the two vehicles. The second vehicle should also have their hazard flashers on, as well as their headlights if it is dark or visibility is poor.
Any passengers or others who are not involved in the tire changing process should stand well back from the road and vehicles. Somebody should help watch oncoming traffic and wave if necessary to warn other motorists to pull out and around your vehicles.
The first step in changing the tire is to make sure your vehicle won't roll forwards or backwards when the flat tire is raised off the ground. Place the transmission in Park if it is an automatic, or in 1st or 2nd gear if it is a stick shift. Also set the parking brake.
WARNING!: On rear wheel drive vehicles, the parking brake and transmission lock the rear wheels only. If your vehicle has rear-wheel drive, and you raise one of the rear wheels off the ground, your vehicle could roll forwards or backwards if the road is tilted or sloped even slightly and the parking brake doesn't hold. The same can happen with a front wheel drive car if your raise a front wheel to change a tire and the parking brake on the rear wheels doesn't hold. You don't want the vehicle to move when you are trying to change a flat tire. To prevent this from happening, wedge two blocks of wood, two bricks, some large rocks or other objects under BOTH sides of one of the tires on the other end of the vehicle from the flat tire. If a rear tire is flat, wedge or block a front wheel. If a front tire is flat, wedge or block a rear wheel. This should prevent any unwanted movement when the flat tire is raised.
DO NOT attempt to change a flat tire on a vehicle if you are parked on a hill or slope. Move the vehicle to flatter ground if possible before attempting to change the tire. If this is not possible, call a tow truck, or attempt to reinflate the flat tire using an aerosol can of inflator/sealer.
NOTE: if your vehicle has a Tire Pressure Monitoring System with pressure sensors inside the wheels, DO NOT use aerosol inflator/sealer unless the product says it is safe for TPMS applications. The sealer in some of these products may gum up the sensors.)
After blocking the wheels, locate the jack, lug nut wrench and spare tire in your vehicle. If you don't know where it is, check your owners manual in the glovebox. Jacks are usually located in the trunk or cargo area of the vehicle, and are usually hidden under a panel or cover. The spare tire may be in the trunk, mounted underneath the back of the vehicle, or hung on the rear door in the case of many SUVs. Some vehicles do not have a spare tire (MINI and Corvette are two). Most vehicles that do not have spares are factory-equipped with run-flat tires that can support the vehicle for distances of up to 50 miles at speeds of up to 45 mph. But if the original run-flat tires have been replaced with ordinary tires, your only options if you have a flat are to attempt top reinflate the tire with a can of inflator/sealer, remove the flat tire and take it to a tire dealer or other facility for repairs, or to call a tow truck.
The positioning of the jack is very important so it will lift the vehicle properly and not damage anything or slip. The old fashioned bumper jacks from the 1960s and 1970s have been replaced with small scissors jacks that are positioned under the side sill of the body or suspension lift points. Refer to your vehicle owners manual for the correct location where to place the jack.
CAUTION: Not placing the jack properly may damage the vehicle or cause it to slip while raising the vehicle.
Remove the spare tire from the trunk or under your vehicle BEFORE you raise the vehicle with your jack.
Loosen the lug nuts BEFORE you raise the flat tire off the ground. The weight of the vehicle on the wheel will prevent it from turning as you attempt to loosen the lug nuts.
To loosen the lug nuts, you may have to remove a hubcap, wheel cover or nut covers on the wheel. Hubcaps and wheel covers, including the small ones that just cover the lug nuts in the center of the wheel, are usually pried off. The lug wrench may have a flat on the end of the handle for this purpose. Otherwise you may have to use a screwdriver or similar tool to pry the cover off. Once the lug nuts are exposed, slip the lug wrench over one of the nuts and turn it COUNTERCLOCKWISE to loosen it. Just loosen it a bit. Don't turn it more than half a revolution. Then loosen the next lug nut and so on until all have been loosened.
Loosening lug nuts is a LOT harder than it sounds because the nuts are tightened with considerable force (typically 60 to 80 ft. lbs. of torque or more depending on the vehicle, type of wheels and lug nuts). Most OEM lug wrenches are about worthless because they are too short and donít' provide much leverage. The L-shaped handle often slips off when you try to loosen the lug nut.
If some moron at a repair shop or tire dealer over-tightened the lug nuts with an impact wrench that last time the tires were rotated or changed, good luck getting them loose with your puny little OEM lug wrench. You're going to need a stout four-way lug wrench, breaker bar or impact wrench to get them loose if they are frozen solid and won't budge. TIP: Carry a four-way lug wrench in your trunk or a 12-volt portable impact wrench for changing tires.
Once all of the lug nuts have been loosened, crank the jack to raise the tire off the ground. You only need enough height so you can remove the wheel and mount the spare without hitting the ground. Raising the vehicle too high increases the risk of the vehicle rolling or the jack slipping.
DO NOT place your hands or feet UNDER the tire while removing the flat tire or mounting the spare . This will reduce the risk of injury should the jack slip or the vehicle roll forward or backwards. Grasp the tire from the sides and wiggle the wheel off the hub. Likewise, when you lift the spare tire into place, grasp it from the sides.
When mounting the spare, line up the holes in the wheel with the lugs on the hub, then slip the wheel into place. Install and finger-tighten at least one lug nut before installing and finger-tightening the rest.
Use your lug wrench to LIGHTLY tighten all the lug nuts so they are snug but not fully tightened. Then lower the jack until the tire contacts the ground and the weight of the vehicle is on the tire. Now final tighten all the lug nuts in a star-pattern (opposite lugs moving back and forth in a circle) until they are all tight. Tighten the lug nuts by turning the lug nuts CLOCKWISE.
Ideally, the tightness of the lug nuts should be rechecked later with a torque wrench as the tightness on the lug nuts is very important to prevent the wheel from coming loose. Over-tightening is also bad because it can distort brake rotors and may break the lug stud on the hub or axle.
After all of the lugs have been properly tightened, replace the hub cap, wheel cover or nut covers as needed, then replace the jack and tools in your vehicle. Load up the flat tire and take it to a tire dealer or other repair facility to have it inspected and patched (if possible).
Though do-it-yourself tire plug and patch kits are available in most auto parts stores, our advice is to take your tire to a tire store or repair shop and have it professionally repaired. Jamming a rubber plug into a puncture from the outside of the tire is really only a temporary fix. The recommended way to repair a flat tire is to dismount the tire from the wheel, inspect the inside of the tire, and install a combination tire plug and patch to permanently seal the leak.
Improperly repaired tires can be dangerous because of the risk of a repeat failure. The Rubber Manufacturers Association has specific guidelines for safely repairing tires. Further details can be found at www.betiresmart.org. Some of their recommendations are as follows:
* A tire should NOT be repaired if a puncture is in the shoulder, edge or sidewall of the tire. The curvature and flexing in this area of the tire may cause a patch to come loose.
* A tire MUST be removed from the wheel prior to making any repairs so the inside of the tire can be inspected for damage or previous repairs.
* If the inner liner in the tire has bubbles or damage, or a repair would overlap a previous repair, the tire must be replaced.
* A puncture that is more than 1/4 inch (6 mm) in diameter means the tire is unrepairable.
* A flat tire should be repaired by filling the puncture with a plug AND covering the inside with a patch (or using a one-piece repair patch that includes a plug). Just patching or just plugging a puncture is not an adequate repair. The angle of the puncture must also be less than 25 degrees if using a one-piece plug/patch.
* Repair procedures require cleaning the inner liner, buffing the inner liner to assure good adhesion with the patch, filling the hole with the proper sized plug, using a vulcanizing cement, using a roller to apply the patch, and resealing the inner liner.
* After the repair has been made and the tire has been remounted on the wheel and inflated, the repaired area needs to be checked to make sure the leak has been fixed.
NOTE: Some tire manufacturers say that repairing a speed rated tire voids its speed rating. Some also void the tire warranty, too!