​Cycling facts: Why are new tyres covered in rubber fibres?

Conclusion by Max Fuchs, BIKE editor

The small rubber nubs on new MTB tyres are neither a secret feature nor an indicator of quality. They simply form because air has to escape from the tyre mould during vulcanisation. They play no part in grip, rolling performance or durability – these production residues disappear anyway after the first few kilometres on the trail.

They are produced during the manufacturing process

These rubber flecks – often referred to in English as ‘vent spews’ – are not a deliberate part of the tyre. They form during the vulcanisation process in the tyre mould. You can read here about what vulcanisation is and how an MTB tyre is generally made. When the rubber is injected, the air must escape from the mould. To this end, the mould has numerous tiny vent channels. Excess rubber is forced into these channels, where it cures. When the mould opens, the fine rubber strands remain on the finished tyre.

Do they have a function?

As for handling: no. The nubs do not improve grip or shock absorption, nor do they affect rolling resistance. They are simply a by-product of the manufacturing process and have no impact on performance.

Do you have to cut them off?

No. When driving, the fine rubber strands wear away on their own within a few kilometres. If you want to remove them for aesthetic reasons, you can do so – but it doesn’t offer any technical benefit.

Are lots of nubs a sign of quality?

This, too, is a common misconception. The number or length of the rubber strands says nothing about the quality of the tyre. Rather, it depends on the design of the tyre mould and the vent channels used by the respective manufacturer.

How can you really tell if a tyre is new?

The rubber nubs are, admittedly, a clear indication that the tyre has been used very little, if at all. However, the key factors determining the tyre’s condition are the sharp edges of the tread blocks, an undamaged tread surface, an even tread depth and, above all, whether the tyre runs true. This is because even an unused tyre ages over time – for example, due to UV light, heat or incorrect storage.