There is a great deal of debate going on nowadays about the proper way to repair tires, whether plugs are sufficient for small repairs or whether plugs are dangerous and patches are the only proper way. In fact, this is a debate that has gone on for literally decades. Plugs are an easy and cheap way of repairing small nail holes, while patches are a more involved, more complex and probably safer way of doing much the same thing. Currently there is legislation pending in New York State that would make all plug repairs illegal. Certainly a patch is by far the best way to repair any hole in a tire, but are plugs really unsafe? Here is my view of the matter.
Tire plugs are made of short strips of leather covered with a gooey unvulcanized rubber compound. When forced into a nail hole, the plug fills the hole and the rubber goo vulcanizes under the heat of driving to fully seal the repair. Plug repairs can be made very easily and do not require the tire to be taken off the wheel to repair, although those who claim that repairs can be made with the wheel still on the car have clearly never tried to do so themselves.
To learn to plug a tire yourself, check out Matt Wright's excellent slideshow at About.com Auto Repair. Keep in mind that neither a plug nor patch should ever, ever be used to repair damage that is located within an inch of either sidewall! The sidewall and shoulder areas of the tire will flex too much when rolling and will eventually work any repair loose, often causing an unexpected and catastrophic loss of air while driving.
The advantages of plugs include low cost and simplicity. Despite numerous pronouncements that plugs are inherently unsafe, in my experience the vast majority of plugs will last for the life of the tire. On the other hand it is clearly possible for a plug to fail, and that's never a good thing. Most plug failures occur because the hole is too large for the plug or is otherwise irregularly shaped, in which case the damage should have been patched in the first place.
A patch is an adhesive-backed piece of rubber that is placed on the inside of the tire, with a hanging tail which is threaded through the hole in the tire to act as a plug. The adhesive then vulcanizes when the tire heats up. This is a much stronger and more effective repair, although a patch should still never be used on or close to a sidewall. Patch repairs are generally the province of trained technicians who have the equipment to dismount and remount the tire.
While patches are certainly a stronger repair, they require the tire to be dismounted from the wheel, take longer and generally cost more. On the one hand, this can be a form of overkill for very small nail holes that could as easily be plugged. On the other hand, when it comes to tire safety, overkill cannot easily be described as a bad thing.
One thing to keep in mind about any tire repair is that if the tire has been run on while flat or at low pressure for more than a couple hundred yards, there is a strong likelihood that the sidewalls have been damaged. When a tire begins losing air, the sidewalls begin to collapse. At some point the collapsing sidewalls will fold over and begin to rub against themselves. This process will scrub the rubber liner off the inside of the sidewalls until the sidewall is damaged beyond repair. If you can see a “stripe” of wear circling around the sidewall of the tire that is softer to the touch than the rest of the sidewall, or if you remove the tire and find large quantities of “rubber dust” inside, or if the sidewall has been worn away until you can see the inner structure – do not repair or put air pressure into the tire, as it is highly dangerous.