How to repair a flat tire

    Motor 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.
    A tire, removed from the wheel, which had fix-a-flat used on it

    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.

    Latest development is a water based Sealant to be injected into the tire either through the valve stem either with the valvecore 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 harmfull chemicals and no aerosol gas what so ever. 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 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.


    Fix-A-Flat is an other way to temporarily fix a flat tire. It should not be used on vehicles (usually 2000 and newer) that have internal tire pressure monitoring systems as it may do damage to the sensor, and voids warranty. It should not be used in bicycle, motorcycle, or other tires that use inner tubes as well.

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