This is a question that gets asked a lot, and unfortunately, there is no definitive answer.
Firstly it is important to remember that tire manufacturers and industry associations do not recommend tire plugging as a safe, long-term solution, whether the tire has one plug or more.
Of course, many people plug their tires at home, and they last the tire’s lifetime with no problems at all.
And here lies the difficulty.
If tire manufacturers say they are unsafe, but other DIY car mechanics at home say they last the tire’s lifetime, it is difficult to know whether and how many plugs are safe or not.
It is difficult to assess tire plug safety because the tire really should be removed from the rim to inspect the inside.
With a patch, a tire has to be taken off the rim, and many times other signs of damage become apparent that were invisible until the tire was removed.
As a comparison: Industry guidelines state that a tire should not be patched if it has an existing repair within 16 inches of the first.
You could also extrapolate that the same- if you are confident that plugs are good – would apply to plugging.
It is difficult to find a place on a tire that is 16 inches away from two existing plugs.
Therefore, the maximum number of plugs you could safely plug in a tire would be two also, as this is the maximum distance apart you could safely patch a tire.
Tire Plug Safety Issues
The quality of the plug repair plays a large part in its safety.
Do you know who did the plug?
You should be very wary if you have bought a car with a tire plug already fitted. You won’t know if the previous owner repaired it correctly.
The tire plug may not be safe, and adding another -even if fitted perfectly – will weaken the tire beyond its limits.
Did they use a good-quality kit?
Tire plugs can be durable and last many years.
However, you get what you pay for in life, and cheaper kits – the ones you see on Amazon for $10 that include all the tools may not be of the same quality as the branded kits you’ll find.
The cement may not be as lubricating; the reamer might not do its job as well.
Plug quality affects safety, and the more plugs fitted reduce the safety even further.
Was the area reamed?
The reaming tool widens and cleans the hole before the patch is fitted.
Some plugs are fitted without being reamed out, either because the person doesn’t have one or feels it is an unnecessary step.
Often a drill is used, but this damages the tire rather than preparing the tire for the plug. It rips away the rubber and steel belts underneath.
Was cement or glue used?
Although not always needed, cement helps lubricate the plug as it slides into the hole.
As it can take a lot of effort to push a string plug, especially without cement, there is a chance that the plug couldn’t be pushed through the tire, causing a weak seal.
Was the hole smaller than 6 mm in diameter?
The temptation is always there to repair a hole in a tire, even if it really shouldn’t be. Extra plugs or more cement as often tried to get a good seal.
The maximum diameter hole that can be repaired is 6mm. If the existing plugged hole was more than 6mm, it is unsafe, as will be any subsequent large hole repairs.
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Sometimes a new tire is the better option if your tire is old or has been damaged before.
We recommend Priority Tire. They often have clearance sales that result in the cost of a new tire being little more than the cost of repairing the damaged one.
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If you are unsure about any of these points, the tire plug could be less safe than it would have been if it had been installed in line with the manufacturer’s guidelines.
Bear in mind that although the plugged hole appeared small, any poor repairs or even as much as drilling the hole rather than reaming it can weaken the steel tire belts inside and cause them to separate sometimes at high speeds.
If you have any concerns about the quality of any tire repair, you should get it inspected by a tire shop and have the tire removed from the rim.
This is the only surefire way to guarantee the tire can be repaired safely.
Simple guesswork regarding the safety of a tire plug or two could lead to the tire blowing out and a serious accident.
As tire manufacturers state plugs are not recommended, car insurance also regards plugged tires as unsafe and will not cover the cost of a claim.