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My fiend's BMW X3 AWD rear right, run-flat tire got a quite long cut by that triangle shaped steel object in the picture. We got it plugged and it has not been leaking any air since the last 24 hours:

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However, as far as I know such long cuts really should not be fixed with tire plugs. What is the reason behind this? Could such repairs manifest in anything else than a slow leak returning? For example, something like a tire blowout that would make the driver lose control of vehicle at high speeds?

Also, these are Pirelli run-flat tires with side wall reinforcement that should be drivable with 0psi pressure for 50mi at 50mph speed. So I would imagine that, if the worst case scenario is that the slow leak simply returns, then my friend will replace these almost worn out tires with new ones, if he really has to.

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Because tyre plugs are designed to fill "round" holes made by puncturing objects. Long cuts allow the sides to move apart further as the strength is reduced in the middle, also allows more vertical displacement. This is why there are specifications as to length, width and diameter. I would not suggest testing this repair at (any) speed on the road as it may fail.

  • Would you mind to speculate in what way it would fail? A potential blowout or simply the slow leak returning? Do run-flat tires mitigate blow out consequences? – Hans Solo May 17 '17 at 5:47
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    No, I will not speculate : DON'T use it - if you have any doubt - which obviously you do, then get it looked at by a tyre specialist. – Solar Mike May 17 '17 at 6:15
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    No need to speculate ... all tires have belts. When you puncture a tire with a small object like a nail or a screw, there usually is no worries about the belt becoming an issue. When there's a slice which cuts through a good portion of the belts, failure of the belt can occur very easily, especially where speed is involved. – Pᴀᴜʟsᴛᴇʀ2 May 17 '17 at 16:41
  • @Pᴀᴜʟsᴛᴇʀ2 Thanks, that was one of the doubts sitting in back of my head. After googling up about tire belts and plugs I believe another problem could be that with long cuts the tire belt is more likely to be exposed to air and moisture leading to even more belt fatigue due to corrosion. If I understand correctly "belt failure" (i.e. tire torn apart due to internal pressure) is something way worse than "plug failure" (i.e. plug getting out of the tire and leak simply returning). If you will summarize these comments in answer I will gladly accept that as answer to the question. – Hans Solo May 17 '17 at 17:25

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