Tuesday Thoughts-Why Are Tyres Black?

A couple of mornings ago a box arrived in the mail containing the two new High Roller’s I’d ordered, readying the bike for my next Native North tour. During the process of fitting them, my young niece wandered through the garage and asked what I was doing. “Fitting some new bike tyres” I replied, which was quickly followed up by a “why are they black?” from her. Literally the only thing I could to answer was “they show up the dirt less than white tyres.” Happy with that explanation she wandered off. I was left with a gaping chasm of self-doubt – I’ve ridden mountain bikes for many years, I’ve worked in bike shops and for a number of mountain bike companies - surely I should know something as simple as why the tyres on my bike are black!

After a little research and talking to friends in the industry, it turns out I wasn’t the only one who had to make up amusing answers to ward off the feeling of idiocy as they too didn’t know why tyres were black, or even what goes into a modern mountain bike tyre. This of course prompted me to find out a little more about tyres…

So starting at a logical beginning, a tyre has three elements to it; the tyre bead, the carcass and the tyre tread. The tyre’s bead core determines the diameter that the tyre will become, and consists of either wire bundle or aramid fibres. This is the part you’ll find furthest towards the centre of the tyre and whose job it is to “seat” onto the rim. The carcass is the structure of the tyre, basically anything rubbery on the tyre that isn’t tread. It’s generally a rubber coated textile material, polyamide for example, and is responsible for providing stability for the tyres when rolling and loaded. For differing tyre applications, the tyre carcass is woven in various densities to provide more or less tyre structure, ie XC tyres have a much lower thread count than downhill tyres. Next time you’re in a shop feel the sidewalls of different tyres, you’ll quickly feel the thicker weaved carcass and be able to identify the tyre’s use. The tyres tread is a located where the tyre meets the ground – there are a huge number of tread options for differing circumstances and conditions and we will look at this in a separate article.

The rubber compound itself is a key element in the tyres – this is a fine balance between grip, rolling resistance and wear rate. And these of course will differ greatly across different manufacturers. Schwalbe as an example make their tyres out of number of components;

  • Natural and synthetic rubber

  • Filler, e.g. carbon black, chalk, silica

  • Softeners, e.g. oils and lubricants

  • Anti-aging agents (aromatic amines)

  • Vulcanizing aids, e.g. sulphur

  • Vulcanization accelerators, e.g. zinc oxide

  • Pigments and Dyes

Schwalbe declare that dependent on the compound, the rubber content is around 40-60%. The filler amounts to 15-30% and the remaining components roughly 20-35%.

So it seems one of the filler components, carbon black creates the black colouring of the tyre. It brings a number of features to the tyre such as improved strength, wear and abrasion resistance, creating longevity of the tyre. Another key feature is the UV block provided by carbon black, which helps to resist photochemical degradation of the rubber – in short stops your tyres falling apart when they’re exposed to the sun over long periods.

Now next time you get asked by family member of friend why your tyres are black, you’ll be able to give them a little insight whilst sounding knowledgeable. If you’ve enjoyed this and would like to see more please give it a like on Facebook. If you’d like to submit a question, please leave a comment on Facebook and we’ll feature it soon!

Sources: Schwalbe