I got a vintage bike to commute with (I wanted a heavy one for the exercise) and I was hoping for a flat so I would have an excuse to spend money on a puncture resistant street tire to replace the knobby tire.

After more than a year of hoping for a flat, I got one. While inspecting it I noticed I had two small pieces of glass in the knobs, but the flat turned out to be on the valve neck.

Also, when I took the old tube out, it had what I guess is a Kevlar layer protecting it. I'm not really sure what it is; it is just a brown layer on top of the tube.

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It is "glued" to the tube thanks to the amount of time they were together, but it peels off easily. Also, you can see the flat where the valve meets the tube on last pic.

If it is a puncture protection, I must say it was doing a very good job. And I will probably buy regular cheap slick tires and reuse that and be happy with not wasting expensive material every time the rubber wears out. In fact I will continue wondering why tire manufacturers even insert that layer on the tires at all! Unless someone with more knowledge here has an argument against that layer and in favor of modern puncture resistant tires.

3 Answers 3


That is a tire liner.

I think http://sheldonbrown.com/flats.html is good reading on the topic of liners / flats in general - in particular, he generally doesn't recommend them (and I don't either). He also claims that if they're improperly installed, they can increase the frequency of flats. If you are prone to flats and you've eliminated improper installation, maintenance and riding (pinching the tube, improper inflation, bad rim tape, going down curbs the wrong way, etc.) - by this, I mean the environment forces the flats (such as certain types of thorns, etc.), you may want to invest in a tire with additional puncture protection (like the Bontrager hard-case tires) which eliminates the improper installation issue or thornproof tubes (these are thicker tubes, so thorns only go in partway, and you can pluck them out of the tires), but these all add unnecessary weight (and a bit of expense, and often some more noise) for most people (i.e. people who live outside areas such road hazards exist in reasonable frequency). Otherwise, just get a normal tire and tube and maintain it properly (install rim tape properly, inflate properly). And you should always have a patch kit on hand anyway (and/or a way to get home).

There are also products like Slime - a sealant that goes in your tube and is supposed to patch up punctures. Some mountain bikers swear by it, I think it just causes a mess.

  • Thanks. I decided to buy new back tires only, puncture resistant slicks, thinner than what i had before. and will keep to run the old fat knobies with that liner on the front. seems to be a good economical compromise
    – gcb
    Commented Jan 6, 2014 at 21:37
  • 1
    Why would you run a knobby tire on the road? If you're doing some (light) off roading on a commuter, this makes a bit of sense, but generally, running slicks (which shouldn't be very expensive for 26" commuters) on both tires is the way to go for commuting on roads. See sheldonbrown.com/tires.html for more discussion.
    – Batman
    Commented Jan 6, 2014 at 23:58
  • i couldn't agree with you more. but besides the price, i don't want to be too wasteful. the knobbies (they are actually hybrids) are perfect, and replacing with slicks would do little on performance for a commuter since there is no rain where I live (when I say that I only care about stopping power performance and safety, since i want the worst performer bike as I want the exercise on the commute). So i just keep them and avoid buying/trashing what i don't really need to.
    – gcb
    Commented Jan 8, 2014 at 19:00
  • 2
    That's fair - I've been running a set of Geax Evolutions for more than the 10k miles on my commuter because I got them at a ridiculously low price with no punctures in a long time. The issue with knobbies aside form noise is that knobbies do affect cornering to some extent (the side knobs can squirm out from under you). I'd expect there's some stopping penalty as well, but I don't have anything to quantify it.
    – Batman
    Commented Jan 8, 2014 at 19:47
  • update if anyone interested: decided to get a slimer, slicker tire for the rear. couldn't get a decent slick with puncture protection for less than $80 here, so I just reused that thing. in the new tire. installation was nothing like the sheldon page seems it look like. you just slide it there, fill the tube and it stays in place. I just cut it to length. pretty easy. it is easy to feel it trhu the slick tire to make sure it is in place before you pump. overall it was 10x easier than installing the rim tape properly.
    – gcb
    Commented Jan 27, 2014 at 19:15

Apparently those are "Stop Flat Liners"... and the consensus at bikeforums is that they work well (as i inadvertently learned)

Think i will keep them and get cheap sleeks. may also get a pair for the other bike.


Your options to prevent/reduce flats are:

  • Solid rubber tires. Heavy and very hard riding.
  • Belted tires. These contain a Kevlar belt under the tread. Pretty good puncture resistance, without seriously affecting flexibility and rolling resistance.
  • Tires with a slab of hard rubber under the tread (tires that advertise "puncture resistant" without claiming a belt). Supposedly good puncture resistance but heavier and not as flexible.
  • Extra-thick "thorn resistant" tubes. The outside diameter of the tube is about 4x thicker than the rest, providing pretty good puncture resistance.
  • "Slime". A liquid rubber-like compound injected into the tube (or present in a tube as purchased) which claims to seal small leaks.
  • Tire liners. In addition to the purchased ones it's not unheard of people to fashion them out of an old tire, cut down and with the tread ground off, or some other (vaguely) suitable material.
  • No doubt something else I missed.

In addition, many claim that tubeless tires are more puncture-resistant, but this may be because they're often loaded with a Slime-like sealant. (I've no experience with tubeless bike tires.)

I've had good luck with the Kevlar-belted tires.

  • 1
    I think tubs are supposed to be more resistant to pinch flats, but I'm not aware they're less liable to sharp punctures
    – Useless
    Commented Jan 6, 2014 at 15:32

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