Should I Patch or Plug a Tire?

Car tire
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 I recently got into a debate with a very seasoned mechanic about whether or not I could just plug a tire and go. He had a tire with a screw in it, and I advised that we could simply pull out the screw, insert a tire plug, and the car would be on its way. He argued that this was not entirely safe, and that you needed to remove the tire from the rim and install a patch on the back side of the tire, even if we used a plug to "fill" the hole the screw left behind. Of course, I knew I was right. He also knew that he was right. So we agreed to disagree, but I wanted to write something up to finally explain why it's ok to use a tire plug all by itself, and why you'll probably get 20,000 miles out of that simple $2 plug. One of the greatest inventions in tire technology since the steel belt, the self vulcanizing tire plug. In summary, this is how these conversations go:

When I first began driving in the late 1950's, if you got a nail in your tire the only way to fix it was with a "plug" which would be inserted moments after removing the nail. As radials became more prevalent, dismounting the tire and applying a patch on the inside was apparently the preferred method of repair.
Now I notice that the plug repair technique is making a comeback and in many instances is the preferred method. Please comment about the pros and cons of each method as it applies to todays steel belted radials.

In the old days plugs were used because they were quick and reliable. If the injury was a simple nail, a tire could be repaired in no time. If the tire was cut, then patching was preferred to completely seal the odd shaped hole. Then when radial tires came out it was found that plugs would warp the tire and make them ride differently. That's when patches became the preferred method of repairing a tire. There were two kinds of patches, cold and hot.

The cold patch required buffing the inside of the tire and applying a cement. Then the correct sized patch was placed over the injury and a special tool was used to "stitch" the patch to the tire. I don't mean stitching in the sense it was sewn on, but that this special tool was rolled over the patch until it was sealed against the tire. The drawback to this method was if you didn't do everything perfectly, the patch would leak.

Hot patching involved essentially the same procedure except the patch was heated and melted to the inside of the tire. There was a special heating clamp that went on the tire to do this. It usually took about 15 minutes to heat the patch to the tire. The advantage of this method was that the tire and patch become one piece.

Now we have plugs that are designed to repair radial tires and are self-vulcanizing. That is to say after they heat up from driving, they "melt" into the tire and become one piece. This is again the preferred method because it is much faster to do. If, as in the old days, a tire was cut then patching is the best way to go. Since very few tire shops even deal with patching anymore, a hole in the sidewall or an actual cut in your tire will usually mean that the tire needs to be removed and replaced with a new one. 

If you can find a shop to do it, patching a tire can take about 30 minutes because everything has to be removed to get to the inside walls of the tire. On the other hand, installing a plug takes a few minutes and usually can be done while the tire and even the wheel is still on the car. Patching a tire can cost $10.00 to $15.00. Plugging can cost as little as $2.00 if you do it yourself, but is usually $5-10 at a tire shop.