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Ultimate upgrades: Schmolke carbon bolts

Sam Challis
4 Jan 2017

They hold together bones, parts of aeroplanes and F1 cars, so why not bikes as well?

A masterly understanding of the capabilities of carbon fibre prompted Stefan Schmolke to dream up these bolts just over three years ago. 

‘Carbon fibre has hugely versatile potential beyond that which is currently exploited, I believe,’ says Schmolke, founder of the eponymous carbon fibre brand.

‘So I wanted to see how far we could push things. The first prototypes I tested on my personal bike, but after we had nailed down the consistent manufacture of the bolts, we saw they had promise far beyond the cycling industry.’

Their application now extends into aerospace and automotive projects, where their weight saving of 40% over aluminium bolts offers a significant advantage.

Due to their composition, the bolts expand slightly when they are tightened so they achieve the same internal clamping tension with less torque and are less likely to wiggle loose.

This has proved particularly beneficial in medical applications, where metal plates can be pinned to injured bones more securely and for longer. As Schmolke says, ‘Less surgery is always a good thing.’

The bolts are made of Hexcel’s intermediate-modulus EM7 carbon fibre, which is roughly comparable to Toray T700, as higher-modulus fibres aren’t flexible enough for how the bolts are manufactured.

‘The way they’re made is actually pretty clever,’ says Schmolke. ‘The fibres are orientated at 0° and follow the spiral of the thread, which makes the bolt near impossible to strip.

However, orienting the fibres is difficult and the mould is incredibly complex, so that’s why they are around £6 a bolt.’

The fibres are then heated and pressed as a PEEK matrix is added. PEEK is a thermoplastic composite that Schmolke explains is much better to use than an epoxy resin.

‘You can’t heat epoxy like you can PEEK, which is key to get the bolts of a consistently high quality,’ he says.

If weight weenies are salivating at the chance to shave a few extra grams from their bikes, Schmolke is quick to point out that for the moment the carbon bolts are only of limited use on a bike. 

Talking the torque

‘The required torque to clamp handlebars in stems and seatposts in seat tubes is too high – it risks cracking the bolts – but they’re perfect for use in derailleurs, headsets and on bottle cages,’ he says and, ever the innovator, foresees a solution to allow more widespread use of the bolts.

‘I have seen potential for us to design our own components specifically for these bolts, which would open the door for some truly light weights.’

As it stands, switching all possible alloy bolts for carbon bolts wouldn’t save more than 20g. Nonetheless, Schmolke says they continue to be very popular.

‘I never thought cyclists would like to buy such expensive bolts to save just a few grams. Obviously I underestimated the lengths cyclists will go to!’

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