Flat tire - AbsoluteAstronomy.com

A flat tire is a deflated pneumatic tire, which can cause the rim of the wheel to ride on the tire tread or the ground potentially resulting in loss of control of the vehicle or irreparable damage to the tire and wheel.

The most common cause of a flat tire is the puncturing of the tire by a sharp object, such as a nail

Nail (engineering)

In woodworking and construction, a nail is a pin-shaped, sharp object of hard metal or alloy used as a fastener. Formerly wrought iron, today's nails are typically made of steel, often dipped or coated to prevent corrosion in harsh conditions or improve adhesion...

, thereby letting air escape. Depending upon the size of the puncture, the tire may deflate either slowly or rapidly.

Other causes of flat tires include, but are not limited to:

Failure of or damage to the valve stem through which the tire is inflated;
Vandalism, such as allowing air to escape from the valve stem or causing permanent damage through intentional puncturing;
Rubbing of the tire against the road, causing ripping of the tire or separation of the tire and rim by collision with another motor vehicle or other object; or
Excessive wear of the tire tread
Tread
The tread of a tire or track refers to the rubber on its circumference that makes contact with the road. As tires are used, the tread is worn off, limiting its effectiveness in providing traction. A worn tire tread can often be retreaded. The word tread is often used incorrectly to refer to the...

allowing explosive tire failure or allowing any road debris or road imperfections to tear through it.

While some flattened tires, particularly those caused by a slow leak, can be repaired and re-inflated with air, others, especially those from worn tread, must be completely replaced.

Driving or riding with a flat tire

When a flat tire occurs, drivers are advised to slow down gradually and pull off the road in a safe place as soon as possible. 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, the hub assembly, or other parts of the vehicle since they can come into contact with the road surface.

Driving with a flat tire, especially at higher speeds, is dangerous. Since controlling the vehicle becomes more difficult, this may result in a serious, potentially deadly accident.

On a bicycle, a flat tire will compromise handling, as well as profoundly increasing rolling resistance

Rolling resistance

Rolling resistance, sometimes called rolling friction or rolling drag, is the resistance that occurs when a round object such as a ball or tire rolls on a flat surface, in steady velocity straight line motion. It is caused mainly by the deformation of the object, the deformation of the surface, or...

. It is certainly ill-advised to continue cycling on a flat tire and in any case, it is extremely difficult to do.

Motor vehicles

A UK

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

source reports that flat tires account for about 10% of motor vehicle breakdowns

Breakdown (vehicle)

A vehicle breakdown is the operational failure of a motor vehicle in such a way that the underlying problem prevents the vehicle from being operated at all, or impedes the vehicle's operation so much, that it is very difficult or nearly impossible, or dangerous to operate, or else at risk of...

.

Motor vehicles are normally equipped with a kit necessary for changing a flat tire. These include a jack, a tire iron

Tire iron

A tire iron is a specialized metal tool used in working with tires that have inner tubes.Tire irons have not been in common use for automobile tires since the shift to the use of tubeless tires in the late 1950s...

or lug wrench

Lug wrench

Lug wrench is the U.S. name for a type of socket wrench used to turn lug nuts on automobile wheels. In the UK it is commonly known as a wheel brace or wheel wrench....

, and a spare tire

Spare tire

A spare tire is an additional tire carried in a motor vehicle as a replacement for one that goes flat, a blowout, or other emergency...

. However, vehicle air pumps (run by hand-lever, pressure cans, or electric pump) can be used to re-inflate slow-leaking tires.

The most common way to repair a flat tire at the side of the road is to use a canned tire inflator

Canned tire inflator

Canned tire inflators fall under the road assistance product category and are mainly packaged in cold-rolled steel cans. The main function of this type of tire inflator is to provide a quick solution to drivers who experience flat tires...

, also known as "fix-a-flat". This is a can filled with a liquid that is propelled using compressed refrigerant 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. Additionally, new vehicles sold in the US 2008 and after are required by law to have a Tire Pressure Monitoring System (TPMS). TPMS is an active system that measures tire pressure and sends to a central computer. Sophisticated electronic circuitry are mounted inside the valve stem. Tire sealant will destroy the TPMS sensor, requiring that the owner replace it at high cost.

Latest development is a water based Sealant to be injected into the tire either through the valve stem either with the valve core removed or still in the valve. This new type of product is far less hazardous when removing the tire from the rim because it contains far less harmful chemicals and no aerosol gas whatsoever. The sealant can be driven into the tire using a compressor.

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 since it is a temporary repair, it is considered 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 (3.4–4.1 bar) 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.

Bicycles

Thin-walled tires, especially those used in road racing bicycles

Racing bicycle

A racing bicycle, also known as a road bike, is a bicycle designed for competitive road cycling, a sport governed by according to the rules of the Union Cycliste Internationale...

are particularly susceptible to puncture by road debris, such as thorns, and small pieces of glass that would not affect tires with more substantial tread. The equipment needed to repair or replace a bicycle inner tube is comparatively minimal, and frequently carried by cyclists.

On the road, the easiest approach to a flat tire, should a spare inner tube be available, is to replace the tube. The wheel is removed, the tire levered

Tire iron

from the rim and inspected for causes of damage, and the inner tube replaced and wheel inflated. The inner tube may then be repaired at a later date.

The repair of inner tubes may be necessary on the road. Several methods exist to locate a small puncture, including submersion in water, but without a bowl of water available, the simplest method may be to inflate the tube until air can be felt escaping from the puncture. Once located, the puncture is cleaned, and a patch applied. Note that tire valves may also become damaged. In this case, repair of the inner tube will not be possible.

Should damage to the tread of the outer tire be substantial, a tough, self-adhesive patch, known as a boot may additionally be placed inside the tire. Folded paper currency is frequently used as a makeshift boot by cyclists in need.

Racing bicycles frequently use tubular tires, which are glued to a special, flat wheel rim. The use of these is often restricted to circumstances where a full spare wheel is available.

Another approach to preventing punctures of lightweight tires is to use kevlar

Kevlar

Kevlar is the registered trademark for a para-aramid synthetic fiber, related to other aramids such as Nomex and Technora. Developed at DuPont in 1965, this high strength material was first commercially used in the early 1970s as a replacement for steel in racing tires...

belts in the tire tread construction.

Another approach to preventing puncures in bicycle and other tires in general is the use of Slime(tm), a brand name and proprietary type of injectible liquid thick chemical "goo" (citation needed, there are other specific types of such sold in bicycle stores and they also have this brand in car size canisters. This chemical "goo" has a tendency to stick to, and coat the outer wall of the inner tube or tire, thus adding another layer of flexible rubber-type protection on the inside of the inner tube or tire. Many MTB riders, or "Mountain Bike Riders", further pre-treat their tires to prevent serious punctures or to prevent punctures in the first place. There are other brands of this same type of liquid, either in an unpressurized container or pressurized container with inflatable gas which is sold in many auto and bicycle stores. The auto sales version of this "fix a flat" type chemical is sold in America (citation needed for other countries where this is sold).

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, they 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 nut

Lug nut

A lug nut is a fastener, specifically a nut, used to secure a wheel on a vehicle. Typically, lug nuts are found on automobiles, trucks , and other large vehicles utilizing rubber tires.-Design:...

s are bolted very tightly to the wheel, and tires themselves are quite heavy.

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.

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 mi/h 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 its low initial cost, but its 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. It is worth bearing in mind that, in an attempt to decrease theft, numerous cars on the road today (especially those with alloy wheels) may use one or more security caps or nuts on a wheel. These can only be removed with a specific tool which should be present in the car's tool kit. Without this tool it will be difficult to remove a wheel.

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. In the United States, the American Automobile Association

American Automobile Association

AAA , formerly known as the American Automobile Association, is a federation of 51 independently operated motor clubs throughout North America. AAA is a not-for-profit member service organization with more than 51 million members. AAA provides services to its members such as travel, automotive,...

, or AAA 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.

External links

Edmunds.com, changing a flat tire.
Video demonstration of how to change a flat tire
http://www.etyres.co.uk/repairable-area-gauge
http://www.etyres.co.uk/changing-tyre-is-childs-play.html