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Up close you can see at least three 'hairs' of rubber from this picture from the side of my tyre:

enter image description here

Why do they exist? I've heard they are just a bi-product of the manufacturing process.

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Note the technical term for what you are calling "hairs" is "vent spews."[1] As the name indicates, they are a consequence of an important detail of the tire fabrication process.

While liquid rubber is being injected or otherwise forced into the tire mold, air bubbles can form in the rubber or between the rubber and the mold. These bubbles can cause the finished tire to be weakened or malformed. To prevent that, tire manufacturers place vent holes in the mold to allow the air to escape under pressure. Necessarily, some rubber will get forced into these holes, forming the vent spews upon curing (which is the process by which the tire rubber converts from liquid to solid).

These vent spews serve no useful purpose in the finished tire; conversely, they can be removed without consequence.

[1] for some citations, see this ask.com post and this reddit post

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  • nice profile pic!
    – andy256
    Commented May 25, 2016 at 0:29
  • So why are there no marks from the injection ports? In cheap plastic household items, one can see where the injection port was not cut off, but broken off.
    – Vorac
    Commented May 28, 2018 at 18:56
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    @Vorac: Sometimes tire manufacturing does not inject the rubber, but rather put some strips of non cured rubber carefully disposed along tire bead and other reinforcements in a mold that then mechanically applies pressure to force the rubber to conform to the mold. (That is what I meant by "otherwise forced into...") In those cases you would't find an injection port evidence or mark in the finished tire.
    – Jahaziel
    Commented May 28, 2018 at 19:58
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Those are "sprues" -- bits of rubber that went into the vent holes in the tire mold. They serve no purpose.

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    Go cut them off! Except if you want some potential buyer of your tires to be sure they are "brand new" :o) (nail cutters or scissors work best)
    – heltonbiker
    Commented May 31, 2012 at 16:42
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    @heltonbiker: That's a good point. The reason I ask is because I tend to pull them out when I'm bored without realising what I'm doing.
    – Ambo100
    Commented May 31, 2012 at 16:56
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    just normal riding will cause them to fall off, but you can pull them off with no problems to the tire. The only thing to think about it like @heltonbiker said, it lets other people know it is a new tire.
    – BillyNair
    Commented Jun 1, 2012 at 6:04
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    They do serve a purpose: they're new tyre indicators!
    – Hugo
    Commented Jun 1, 2012 at 14:20
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    The one true way to remove them by application of friction between the tire and the road through riding.
    – BPugh
    Commented Aug 22, 2013 at 15:53
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i can only imagine during the manufacturing process that hot rubber is injected into a mold like device and then spun till cool enough to remove, these little hair like things are formed during the centrifuge process through little holes that serve as a way for air to escape to prevent imperfections in the tyre (tire).

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  • 7
    Welcome to bicycles.SX.com. Your answer is correct, but there are already two answers that state exactly the same. So you didn't really add some new aspects to the topic and therefore your answer might not get many upvotes. Maybe you should first look at the answers already posted before you post your own one to see if it is a duplicate.
    – Benedikt Bauer
    Commented Jan 3, 2014 at 21:42

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