I have a small slit in my MTB tyre (approx 3mm long x barely 1mm wide) which won't seal.

I had to put a tube in when the puncture happened as it wouldn't seal, but I've now taken the tube out, cleaned down, remounted and injected fresh sealant. So I know there's plenty of fresh sealant in there.

I inflated the tyre gently a bit at a time and spun the tyre to distribute the sealant and the hole did appear to seal, allowing me to inflate the tyre to 40psi. However, over night the hole has continued to leak a tiny amount of air, leading to the sealant bubbling up on the outside. I can still hear air slowly hissing out of the hole, 12 hours after I would have expected it to seal. Riding caused the leak to open up more (though it then re-sealed to the same low pressure as before).

The hole is so small that I can't understand why it won't seal. I've had other punctures seal ok on these tyres with this brand of sealant.

Are there some punctures that simply won't seal? Or is there something I need to do to make this "sealable?" I have some tubeless tyre plugs, but even the smallest is way way bigger than the hole I've got.

Any suggestions greatly appreciated.


  • Tyre: Maxxis Ardent Race 27.5
  • Sealant: Orange Seal Endurance. Orange Seal state that it can seal punctures up to 1/4", but this is only 1/8" and very narrow.

Best photo I could manage (puncture circled in red, please excuse the other muck on the tyre):


  • Try using the regular sealant, not the endurance formula. I find it too watery to really seal anything beyond casing porosity.
    – MaplePanda
    Aug 20, 2022 at 0:57
  • @MaplePanda that's interesting because I also thought it was rather watery. Will try something else next time. Aug 22, 2022 at 6:41

3 Answers 3


No, 3 mm is not the limit by any means. Through personal experience I have had a 9mm cut (external measurement, internally was likely reduced) seal without any plugs on a road tire. Yes, a road tire at 80 psi, and rideable without any reinflation.

I would NOT expect that to be repeatable, and bacon strip plugs and/or Dyna Plugs are in my saddlebag and/or jersey pocket on ever ride.

Even with holes that seem smaller than the plug you are trying to install, in those situations you just need to punch it through. It seems counter-intuitive as you think you are doing additional damage (and maybe you are), but the plug has got to get in there, so you just do it. It can be difficult to push through on a small hole, so be sure you align exactly on the hole before shoving it in. After you do this a few times, you will not doubt yourself. IMPORTANT: do not push through so far that you hit the rim tape and tear up that seal! Smaller road tires are the most vulnerable to this, but regardless, don't go too far and be careful.

There are some punctures that will not seal with sealant alone. The size of the puncture AND the location of the puncture on the tire play a big role. Without plugs I have found that about 15 minutes has been REQUIRED to get any reasonable hole to seal enough to not loose the latex-sealant "clot" upon riding again. Hot and dry or cold and wet, it still takes the time to create the clot. That is where the self-inserted plugs come in. Upon detection of a leak, you first try to stop the leak by orienting the leak/hole so that the sealant will try to seal it. That usually will slow down or stop the leak. Then you jam in a bacon-strip or dyna-plug into the hole and you can then immediately ride on.

This is what I carry (road/gravel/MTB). Red and blue are Dynaplug options the top one is Genuine Innovations Tubeless Tackle Tire Repair Kit with Bacon Strips (I have used this a dozen time with over 90% success). There are many other options out there as well, with similar success:

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  • 1
    Thanks for the comments about your experience - sounds like fundamentally I'm right to be a bit disappointed that such a small hole didn't seal, but also sounds like it's not completely out of the question. I carry plugs anyway so no big deal I guess. Aug 22, 2022 at 6:45

3mm is often indicated as the limit for the sealant. But you can easily solve that with a "bacon strip," that you can find in tubeless repair kits. (similar item to bacon strip - a DynaPlug).

Here's a tutorial on how to it:


Some sealants don't perform as well at higher pressures, and 40psi is very high for a tubeless MTB tyre which are more typically run between 20-30psi.

You have a few options to try:

  • See if a lower pressure works as long as your weight allows it
  • Make the hole a little bigger and use a tubeless plug
  • Take the tyre off, clean it up and apply a tyre boot before setting up tubeless again
  • Just for interest, I normally ride 25-30psi but my thinking was that if I go hard into a berm or similar then the pressure is going to spike briefly, and I want some confidence that I'm not going to blow the seal mid-ride. Hence inflating to a higher than normal pressure to try to test that. Aug 22, 2022 at 6:47

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