Flat tire

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See also: Run-flat tire
A flat tire on an automobile.

A flat tire (British English: flat tyre) 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. The most common cause of a flat tire is puncturing of the tire by a sharp object, such as a nail, letting air escape. Depending on the size of the puncture, the tire may deflate slowly or rapidly.[1]

Other causes[edit]

  • Failure of or damage to the valve stem;
  • Rubbing of the tire against the road, ripping the tire, or separation of tire and rim by collision with another object;
  • Excessive wear of the tire tread allowing explosive tire failure or allowing road debris to tear through it.

Some tires, particularly a slow leak, can be repaired and re-inflated; others, especially those from worn tread, must be replaced.

Driving or riding with a flat tire[edit]

When a flat tire occurs, drivers are advised to slow gradually and pull off the road.[2] Continuing to drive may damage the wheel, the hub or other parts of the vehicle. Driving with a flat tire, especially at high speeds, may result in a deadly accident.

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

Flat tire repair[edit]

Motor vehicles[edit]

A UK source reports that flat tires account for about 10% of motor vehicle breakdowns.[3]

Motor vehicles are normally equipped for changing a tire. These include a jack, a tire iron or lug wrench, and a spare tire. Air pumps run by hand-lever, pressure cans, or electricity can be used to re-inflate slow-leaking tires.

One common way to temporarily repair and re-inflate a punctured tire at the roadside is to use a canned tire inflator. The motorist attaches this to the valve, and the compressed refrigerant inside forces the can's contents through the valve into the tire. There the liquid is forced towards the puncture and will block the hole. Tire sealant is typically useful on punctures of 3/16in. diameter or less. Tire sealant creates a hazard due to harmful chemicals and the possibility of sealant shooting out of the valve stem at pressure. Many modern vehicles are fitted with tire-pressure monitoring systems which employ sensors in the valve stem to measure tire pressure; these sensors may be blocked or destroyed by a roadside tire sealant.

A water-based sealant can be injected into the tire either through the valve stem. This contains less harmful chemical and no aerosol gas. The sealant can be driven into the tire using a compressor.

A flat tire can be repaired by a patch or plug; or the tire may repair itself. Self-sealing tires work on punctures up to a certain size.

The patch repair is commonly used in repair shop. Some may not patch a worn tire if: the hole is close to a previous patch, there are already more than two patches, the puncture requires more than two patches, the punctures are too close, and/or the puncture is close to the sidewall. A patch is performed by removing the tire, marking the puncture, scouring the surface to create a smooth surface inside of the tire), applying rubber cement, applying the patch, then pressing it to the surface with a small metal wheel attached to a handle. An alternative is a combination patch and plug. This is manufactured with a plug built into it; applying this patch is done similarly except with more steps, including drilling a hole at the puncture so the plug can be pulled through it, as well as cutting off the excess plug from the outside the tire.

The final method, the tire plug, can be performed without removing the tire. The puncture is removed from the tire, and a plug coated in rubber cement then inserted with a handle, typically supplied with the kit. Many technicians consider plugs less reliable than patching though more reliable than sealant.

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 with dish soap 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[edit]

Thin-walled tires, especially those used in road racing bicycles 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 from the rim and inspected for causes of damage, and the inner tube replaced and wheel inflated. Re-inflation can be carried out by the use of a frame mounted pump or a CO2 cartridge inflator. The CO2 cartridge is generally a single use item only while the pump can be used to inflate many flat tires. 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 with dish soap, 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 (see Louis Rustin for the invention of the puncture patch). Note that tire valves may also become damaged. In this case, repair of the inner tube will not be possible, and the tube should be replaced.

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 belts in the tire tread construction.

Another approach to preventing punctures in bicycle and other tires in general is the use of Slime, a proprietary brand of injectable liquid thick chemical goo.[citation needed] 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 of chemical is sold in America.[citation needed]

Dangers of changing a flat tire[edit]

Motorists stranded by a flat tire face a number of hazards.

The most common hazard is from the passing traffic.[citation needed] Especially if the tire is on the side closer to the road, the motorist is at risk of 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, 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 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[edit]

A tire blow-out that occurred due to improper maintenance.

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 (80 km/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, or AAA (pronounced "triple-A") and in Australia National Roads and Motorists' Association or NRMA are 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.

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