It’s not unusual for silly and rather pointless questions to tumble through my mind. A hairbrain if you will, and this time, it’s about actual hairs, or at least, the hairs seen on some tyres.
Technically known as vent spews, the little hairs that protrude from some new tyres exist thanks to the manufacturing process. What are they and why aren’t they removed at the factory? Does leaving them present carry any negatives? And if you were to remove them, how do you best do that? These are the things that nobody really asks that I aim to answer.
Vent spews explained
While tyre manufacturers each have different methods for molding a tyre’s rubber, the hairs in question reveal one of the more common approaches.
“Micro vents are needed to vent the mold during vulcanization of the tyre, to ensure the rubber is distributed evenly and no air is trapped between mold & rubber,” explained Continental Road/Race product manager, Hannah Ferle.
For Continental, as on other brands' other slick road tyres, you won’t typically see these hairs or venting spews, at least not as prominently as the mountain bike tyre pictured up top. According to Ferle, that’s because the smaller mold combined with a simpler shape (no sharp edges or knobs) means far less areas for air to be trapped between the rubber and the mold.
Some road tyres (such as Pirelli) are incredibly clean out of the box without obvious vent spews or lines, while many others (such as Vittoria) have more obvious remnants of molding.
“Also, explaining to customers why their slick road tyre suddenly has a better hairstyle than them would be tricky,” joked Ferle. Instead, and at least for Continental road tyres, you’ll typically see more subtle venting lines (aka, flash) on the sidewall and centre of the tread which are created through purposeful gaps in the molds.
By contrast, more complex tread shapes, or perhaps even where multiple compounds are used, will typically present more vent spews compared to a simpler tyre. “That’s why you typically see these “rubber hairs” only on tyres with complex profiles e.g. gravel, MTB, sometimes urban,” wrote Ferle. And indeed, Continental’s knobby tyres do often look like a hedgehog out of the box.
You’ll also find those hairs on the knobs of off-road tyres from Schwalbe, or the sidewalls of Maxxis tyres, and countless other examples. And it’s not uncommon to see a combination of both vent spews and vent lines on a single tyre.
Either way, they exist on many tyres, including those found on motorcycles and cars, and most manufacturers leave them be because they don’t affect much and there is no great time or cost-efficient way to remove them at scale.
To remove or not to remove?
It’s an age-old question. These vent spews will eventually wear away with use, but should you remove them?
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