On a beater bike I've got (25 year old Raleigh MTB) I run tyre liners because I had spare tyres and was too cheap to buy good anti-puncture ones. They do their job quite well -- I've just picked broken glass out that had gone through the tread but stopped at the liner.

But the reason I found the broken glass was that I had a flat. I knew the tyre was a bit soft but over the weekend it went right down. On inspection I saw this on the outside of the tube:

Strange puncture

That curve matches the end of the liner, and with enough air in the tube I could feel it leaking.

The liner doesn't feel like it has a rough edge (we'll find out because I left the liner in with a new tube), and it's been running fine for over a year. This would appear to defeat the point of liners, so am I missing something? Does too high pressure cause this? Too low?

  • I've used tire liners before, but mine had a straight edge rather than a curved end like yours has. I didn't cause any marks like your picture is showing from what I remembered. What size tires and pressure are you running? Did this happen on the front or rear of the bike? Was the curve facing the front or the rear of the bike? Does the other inner tube have a similar marking?
    – Kibbee
    Mar 14, 2017 at 14:04
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    If I had to guess I would suggest your tire pressure may be too low. Have you tried adding some smooth tape (e.g., a couple layers of electrical tape) over the end of the tire liner to present a smooth surface to the tube?
    – Rider_X
    Mar 14, 2017 at 14:05
  • @Kibbee 26x1.95. Sidewall pressure is 65psi max, I normally pump up to a generous 65 but not very often, so it was probably more like 40--45 recently (I've also learnt the hard way recently not to trust the gauge on my decent portable pump). This was the front wheel, but I can't remember which way it was facing. I haven't taken the back wheel off to have a look, but it's holding pressure quite well.
    – Chris H
    Mar 14, 2017 at 14:09
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    @Paparazzi that's could be similar to what I'm seeing then (though this bike doesn't do much distance), but there's so much debris on the roads round here that it probably still saves me tubes. The bike essentially has zero value and I assume it's going to get stolen sooner or later (or rust away to nothing) so I don't want to buy marathon plus
    – Chris H
    Mar 14, 2017 at 15:22
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    After a similar pinch flat, my LBS rounded the edges of the ends of the liner.
    – Mike Chess
    Mar 16, 2017 at 19:22

1 Answer 1


I've never seen this exact flat, but I can see how it can happen. It's why some brands of liners now have rubber tips at the ends of them. a little filing just to be sure it's smooth there with an emery board should take care of it. Or as suggested in the comments, a piece of electrical tape should help.

  • The electrical tape did the trick in the end
    – Chris H
    Feb 13, 2020 at 9:24

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