Flat tire
From Wikipedia, the free encyclopedia
- See also: Run-flat tire
In a motor vehicle, a flat tire occurs when a tire becomes deflated and the metal of the wheel comes in contact with the ground below (or ground level). This can occur for several reasons: [1]
- The tread of the tire wears down, exposing a hole in the tire. This occurs through normal wear-and-tear, and may be expedited when various conditions are not optimal.
- A foreign object, such as a nail, pierces a hole in the tire, thereby letting out the air. Depending on the size of the hole, the tire may deflate slowly or rapidly. Some tires are flattened through acts of vandalism.
- A tire may be damaged in a collision with another vehicle or an object that causes the rubber of the tire to separate from the wheel, or that rips the tire to shreds.
A bicycle may also suffer a flat tire when the inner tube becomes deflated, damaged, or is worn.
Flat tires account for about 10% of motor vehicle breakdowns.[2]
While some flattened tires, particularly those caused by a slow leak, can be restored and refilled with air, others, especially those from worn tread, must be completely replaced.
Vehicles are normally equipped with a kit necessary for changing a flat tire. These include a jack, a tire iron or lug wrench, and a spare tire. However, vehicle air pumps (run by hand-lever, pressure cans, or electric pump) can be used to re-inflate slow-leaking tires.
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[edit] Driving with a flat tire
When a flat tire occurs, it is best to slow down gradually and pull off the road in a safe place as soon as possible. [3] Continuing to drive after a tire becomes flat may be extremely hazardous. If there is any chance of patching a leak and restoring a tire, it will be diminished if the car continues to be driven. Continuing to drive may also cause damage to the wheel or other parts of the vehicle.
Driving with a flat tire, especially at higher speeds, may also be dangerous. Since controlling the vehicle becomes more difficult, this may result in a serious, potentially deadly accident.
[edit] Dangers of changing a flat tire
Motorists stranded by a flat tire face a number of hazards.
The most common hazard is from the passing traffic. Especially if the tire is on the side closer to the road, the motorist is at risk from getting hit by a passing car. If the motorist is unable to pull over to a place where the tire being changed is on the opposite side from the moving traffic, s/he may be directly in the path of or just inches away from passing cars. Even if some type of warning is placed on the road, a motorist not fully attentive may not be able to avoid the situation.
Some motorists, especially those with less physical strength, may risk injury while attempting to change a tire. Often, lug nuts are bolted very tight to the wheel, and tires themselves are quite heavy.
In some cases, the stranded motorist faces the dangers of crime, even in a seemingly safe area. In 1997, Ennis Cosby, the son of Bill Cosby, was murdered while changing a flat tire.
While the use of a run-flat tire can prevent these problems, some run-flat tires have other inherent flaws that make them less appealing.
[edit] Flat Tire Repair
The most common way to repair a flat tire at the side of the road is to use a can of tire sealant, also known as "fix-a-flat". This is a can filled with a liquid that is propelled using compressed air inside the can into the tire via a flexible tube attached to the valve stem. Once inside the tire, the liquid is forced towards the puncture and will block the hole created by the puncture. Tire sealant is typically only useful on punctures of 3/16in. diameter or less. Tire sealant also creates a hazard for the technician removing the old tire from the wheel, due to both the possibility of exposure to harmful chemicals used in the sealant; as well as the possibility of the sealant shooting out of the valve stem at high pressure.
There are multiple ways to repair a flat tire, including using a patch or plug; or alternatively the tire may repair itself. Self-sealing tires are a relatively recent innovation and only works on punctures up to a certain size.
The patch method of repair is commonly used in automotive repair shops, with some shops having a policy against patching should the tire's tread be below what would be considered safe, if the patch is too close to a previous patch, if there are more than two patches performed previously, if the amount of punctures requires more than two patches, if the punctures requiring a patch are too close to each other, and finally if the puncture is too close to the sidewall of the tire. A patch is performed by first removing the tire from the wheel, marking the location of the puncture (typically with a dedicated "tire crayon"), removing the puncture, preparing the surface using an angle grinder (or via other methods, done to create a smooth surface on the inside of the tire), applying rubber cement to the prepped area, applying the patch, and then pressing it onto the surface with a tire stitcher (a small metal wheel attached to a handle, looking similar to and sometimes known as a "pizza cutter"). An alternative patch, considered by some to be safer and more reliable, is a combination patch and plug. This patch is manufactured with a plug built into it; applying this patch is done very similarly to the way a regular patch is applied except with a few more steps. The additional steps include drilling a hole at the location of the puncture so the plug can be pulled through it, as well as cutting off the excess plug from the outside of the tire.
The final method, the tire plug, is able to be performed without removing the tire from the wheel. The puncture is removed from the tire, and a plug coated in rubber cement is then inserted with a handle, which is typically supplied with the kit the plug came in. Many automotive technicians consider plugs to be less reliable than patching, though more reliable than tire sealant. A tire plug is a good idea for those who notice a puncture in a tire that they aren't able to professionally repair at the time.
One disadvantage of patching a tire is that due to the process requiring one to remove the tire from the wheel, the tire must be balanced again when it is put back on the wheel. Tire sealant also creates an imbalance in the tire, but due to it not being a repair that could be considered reliably permanent, this is less of an issue. However, the issue of disposal of the tire sealant, hazards to the technician, as well as the required cleaning of both the inside of the tire as well as the wheel could all be considered disadvantages of tire sealant.
Tires can leak air due to a variety of reasons. These include, but are not limited to: damage to the wheel itself, a damaged valve stem, a puncture in the tire (which sometimes can be hard to find if the puncture didn't embed itself in the tire, which among other reasons can happen by running over a board with nails sticking out, for example) and improper installation of the tire, which could involve the bead of the tire being cut when installed with excessive force.
Occasionally, a puncture may not "go all the way through" to the inside of the tire. Thus, before coming to the conclusion that a puncture is causing air to leak from the tire, attempt to remove the puncture lightly by hand. It's very possible that the head of a nail or a very short nail created the appearance of a puncture, while not actually being one.
Also worth mentioning is the fact that tires simply lose air over time. A brand new tire, properly inflated, will lose air even with no punctures present. This is mainly due to the design of the valve stem, among other reasons. Given enough time, a tire can fully deflate with no outside intervention.
Should one be so inclined, one way to locate the source of a leak in a tire (a standard passenger tire being used for this example) is to inflate the tire to 50-60 psi and place the tire and wheel in a tank of water and watch for bubbles. This method may not work all the time, especially with very small punctures, but may help one find a possible leak.
[edit] Prevention
The best way to avoid a flat tire is to avoid situations favorable to tire punctures. These involve driving through construction sites, or areas with heavy construction activity (new housing developments, for example), driving unnecessarily on roads with rough surfaces, as well as driving over debris, to list a few. There are, however, other methods one can use to avoid getting stuck with a flat.
One highly important preventative measure in avoiding a flat is to ensure your spare tire is properly inflated and in good, undamaged condition. If the spare tire has an irregular sidewall (bumps, dents, or other deformities) the spare tire needs to be replaced. Also check for dry rot (which looks like small cracks in the sidewall) as well as good tread depth. New spare tires can be purchased at tire repair shops, automotive dealerships, even over the internet. If for any reason, the process of checking the inflation pressure of your spare is too arduous of a task for you to perform (on some vehicles this requires removing the spare tire [which, if a full-size, could be very heavy] or sliding underneath the vehicle [common on SUVs and pick-up trucks]); when getting an oil change done or other routine maintenance one can (and should) request that the technician working on their car checks the spare tire pressure. If one chooses this route, it will help the technician if you remove items that may block access to the spare tire. Most auto technicians will only check the pressures of the tires already on the vehicle, and will ignore the spare tire unless one requests it be checked.
Of course, it is always a good idea to have a can of fix-a-flat should your car not have a spare; or use of a spare is inconvenient (most compact spares have a safe maximum speed of 50 mph and a limited distance), as well as in case the vehicle's spare is damaged, missing, or severely under-inflated. It is also a good idea to have a roadside safety kit, which usually includes a reflective triangle to be placed further down the road to let other motorists know a hazard lies ahead.
Items that can help while changing a flat include an "emergency impact wrench", an impact wrench that plugs into your car's cigarette lighter, or on cars without a cigarette lighter, the car's 12-volt accessory outlet. This item can greatly decrease the amount of effort required to remove the lug nuts from the tire to be removed, also decreasing the amount of time required to change a flat. Also available are portable air compressors that are very compact and affordable, and can also be plugged into the cigarette lighter/accessory outlet to inflate an under-inflated tire. In the event of a slow leak, this may greatly help extend the driving range of the affected tire, allowing the driver to reach a location where the driver can properly attend to the affected tire.
A much more active approach to monitoring tire pressures involves retrofitting a tire pressure monitor to your vehicle. Vehicles manufactured after model year 2007 are required to have tire pressure monitoring systems built-in, although many older vehicles might not have it. Tire Rack, for example, offers aftermarket tire pressure monitors from various companies, including one that notifies the driver of the tire pressure in each wheel, as well as exactly which tire the system is displaying the pressure of. A much less expensive way to monitor tire pressures is to install valve stem caps that alert the driver to low tire pressure. These work by first setting the pressure on the cap matching the pressure you desire your tires to be at. Once installed on the tire's valve stem, the tip of these caps will change color (from green, to yellow, to red) when the tire becomes under-inflated. The benefit of this system is it's low initial cost, but it's disadvantages include questionable accuracy (even more so if the caps aren't tightened down enough) and that the only way to monitor them is from outside of the vehicle, looking directly at the cap. It's always a good idea to have a quality, reliable tire gauge on hand regardless of what system is installed in your vehicle, and to either check tire pressures yourself of by having someone else do it, as most tire pressure monitor systems will not alert the driver until the tire pressure falls below a certain amount, usually 20% below the recommended pressure.
Also important is knowing the condition of the spare tire, jack and lug wrench upon purchase of a used car. This, among other things, is one very important item many used car buyers overlook when inspecting a potential purchase. If the vehicle is missing any of the items that go with a spare tire, it's possible to purchase them again from the manufacturer's dealership. It's also possible to buy the tools used, or from a junkyard, though if one chooses this route it is of utmost importance that the condition of the items be inspected thoroughly before storing them in your car. It's also possible to purchase a jack and a universal lug nut wrench (usually shaped like a + sign) from an auto parts store or the automotive section of a department store, though these items will likely not fit in the vehicles designated spare tire tool storage location and will likely require that the items remain loose in the cargo area.
If you happen to be stuck with a flat tire and are unable to change the spare tire yourself, or encounter other problems with your vehicle that leave you stuck at the side of the road, it's always a good idea to have a membership to, and carry a card for an auto club, or a roadside assistance agency. The American Automobile Association, or AAA (pronounced "triple-A") is one of the most well known roadside assistance programs and will gladly change a flat tire for you. Lesser known programs include those that are a feature of your auto insurance coverage, as well as manufacturer roadside assistance (which comes with most new cars), and even plans offered by cellular phone providers, Verizon Wireless being one example.
[edit] See also
- Tweel - Michelin's air-free tire
- Tire manufacturing
- Tire Pressure Monitoring System
- Tire mousse
[edit] References
[edit] External links
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