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Carbon jargon: What does it all mean?

Martin Graham
24 Sep 2018

We unravel the mysteries of weaves, tows and moduli that accompany anything carbon-related

You’re in the market for a new bike. Carbon, of course. It’s the miracle material that offers stiffness and lightness in abundance and has changed the face of the bike industry. But which to choose? Every manufacturer makes claims that its carbon is somehow superior to its competitors, aiming to dazzle you with phrases such as ‘unidirectional’, ‘ultra-high modulus’ and ‘1k weave’. 

It’s not always obvious what any of these terms really means or what they tell you about the bike you are considering buying.

With very little regulation on how marketers use these phrases, it can be a minefield trying to decipher the jargon, so Cyclist has approached the experts to get the truth behind the sales pitch.

A question of quality

Carbon fibre is made up of filaments. In simple terms, a carbon fibre filament is an incredibly thin strand made up mainly of carbon atoms.

Alan Riley of carbon manufacturer Toray says, ‘The raw material we use is acrylonitrile (AN) which derives from oil, which goes through a process that makes polyacrylonitrile (PAN), which is a sort of white fibre.’

LaRhea McBee, technical support engineer from Hexcel Composites, adds, ‘In step two, PAN undergoes oxidation and carbonisation through heat treatment and stretching to form carbon fibre. The modulus of the carbon fibre is directly related to the final heat treatment temperature.’

As the temperature rises to between 400 & 1,200°C, ordered microscopic ‘crystals’ of carbon emerge, ‘improving ordering and orientation of crystallites along the fibre direction,’ says McBee.

The hotter the heat treatment, the higher the modulus, and it’s the cost of working at these intense temperatures that is reflected in the price of the highest modulus carbon fibres.

Riley says, ‘In the bicycle industry our business is mainly carbon fibre raw material thread. That’s sent to a weaver who makes it into a textile fabric, which goes to a pre-pregger [to add uncured resin], who sends it to a moulder who makes the frames.’ [A process you can read more about here]

But going back; thousands of these filaments can be bundled together to make a thread that is both very strong and very light.

This can then be woven into a fabric, shaped to make tubes and components, and combined with a resin to make them solid. Hey presto – a bike!

But are there different qualities of carbon fibre? Toray's Alan Riley says, ‘Carbon fibre is only strong in one direction so the alignment of the fibres is very important.

Quality is about keeping the alignment very consistent, very controlled. A low quality fibre will be where the filaments of the fibre are frayed or broken, or where the tow width of the fibres varies from batch to batch.’

So how do you know if your bike uses high-quality or low-quality carbon? Fortunately the quality tends to be kept in check simply because there are very few suppliers of carbon fibre to the bike industry and, as Riley says, ‘The quality of the final product reflects on us as a supplier.’

Toray, along with other global companies such as Mitsubishi and Hexcel, supply the bulk of carbon fibre to the major bike manufacturers and factories in the Far East, which means there won’t be a huge difference in the quality of the raw material from brand to brand.

Trek’s composite manufacturing engineer, Jim Colegrove, says, ‘It’s like the [bike] industry doesn’t want to say which fibre they are using definitively because in many cases their competitor is using the same fibre. Brands want you to believe that there are hundreds of options, but when it comes to the number of different fibres, there are really only a few.’

And Riley adds, ‘No brands get exclusivity on carbon fibres.’

However, just because the quality of the raw material may be dependable, doesn’t mean that all carbon fibres are the same.

There are many different grades of carbon fibre and the main differences between them come down to the strange science of modulus.

Attack of the moduli

A favourite phrase of the marketing men is ‘ultra-high modulus’ (UHM). It refers to a grade of carbon fibre that is very stiff and very light (and very expensive), thereby suggesting that the resulting bike will be exceptionally stiff and light too.

But, as always, it’s not quite as simple as that.

‘Our carbon fibres fall generally into three grades: standard, high and ultra-high modulus,’ says Riley at Toray.

‘For example, M65 is what Pinarello uses [on its Dogma 65.1]. It’s very high modulus and it’s a very, very expensive material that can run into the thousands of euros per kilogram of thread.’

Indeed, the marketing blurb for the Pinarello Dogma states, ‘The Dogma uses the best carbon fibre available: Torayca 65Ton HM 1K with nanoalloy technology,’ but what it fails to mention is that the whole bike is very unlikely to be built exclusively from this ultra-stiff, ultra-light, ultra-high modulus fibre.

Richard Matthews, senior engineer at Cervélo, says, ‘We take great care in where we place HM [high modulus] material because higher modulus fibres almost always have lower strength properties than lower modulus fibres.

'Weight reduction almost always comes at the cost of robustness. However, clever laminate design and material choices can improve robustness with less weight penalty.’

What he means is that even though high and ultra-high modulus fibres are stiffer, they tend to be more brittle and prone to breakage than standard fibres, so their use has to be restricted to areas on the bike where load forces will not compromise the frame.

It’s down to the engineer to decide how much of each grade of carbon fibre to use, and where to place it, to get the best balance of weight, stiffness and robustness in the finished frame.

It’s a view echoed by Craig Calfee of US-based bike manufacturer Calfee Design: ‘Use of higher modulus carbon fibre will generally result in a lighter bike, all other things being equal, but it usually comes at the expense of toughness.

'If you can afford to own an expensive bike made with the more exotic materials, be prepared to afford the repair or replacement in the event of a minor mishap.’

So even though your prospective new bike claims to use UHM carbon fibres, it’s virtually impossible to know how much UHM is present in the frame or what effect it will have on the ride quality.

Riley says, ‘I suppose if they use it then they can say it’s UHM, but it should come down to whether the UHM actually adds any kind of mechanical performance to the bike. Otherwise you could just stick a patch on and say it’s a UHM frame.’ 

Colegrove adds, ‘Making a bike that feels great is more than just simple stiffness-to-weight, so just quoting a fibre type isn’t the answer.’

Another issue with ultra-high modulus is that it doesn’t refer to a specific grade of carbon fibre, rather a spectrum of stiffness that will differ from supplier to supplier.

So one man’s UHM could be another’s standard grade. Until there is more transparency in the use of marketing terminology, it will come down to how much you trust the brand you’re considering giving your money to. 

One direction

‘The word “unidirectional” frustrates me,’ says Riley at Toray, ‘because it isn’t really any kind of performance indicator; it just explains the orientation of the fibres. All it means is that the fibres are put through the prepreg machine in just one direction, as opposed to being in a woven fabric.’

Unidirectional (UD) carbon fibre – another favourite of marketing spiels – is where the fibres are all laid along the same path before being bonded by resin in the aforementioned ‘prepreg machine’.

As carbon fibres are strong in one direction only, this allows the sheet of carbon fibres to remain strong (in one direction) while keeping weight to a minimum. Woven fabrics have fibres running in different directions (usually perpendicular to each other), which improves robustness but adds bulk. 

According to Calfee, ‘There is not really a time when woven is better than UD. Woven materials are used mainly for cosmetics and to prevent splintering when cutting.’

The cosmetic side of woven fabrics is not lost on Riley, who says, ‘Sometimes if people can’t see the weave pattern they don’t think it’s carbon fibre.’

However, Matthews at Cervélo believes there are times when it makes sense to accept the added weight of woven fabrics: ‘They have some higher strength properties and more damage tolerance than UD.

'Its place is where there are abrupt changes in shape or on localised high-stress areas such as holes for cables.’

As with modulus, unidirectional carbon fibre offers performance benefits only when used judiciously. Too much in the wrong places will make for a light but potentially brittle frame, and it’s no guarantee of a high-quality bike.

As Colegrove says, ‘Importantly, the layup must be changed to take into account different material properties.’

Resins to be cheerful

When it comes to marketing jargon, one area that is rarely given much fanfare is the resin. This is the glue that holds the floppy fibres together and which, once cured in an oven, makes the whole structure rigid.

Colegrove has his own thoughts about why resins don’t get much of a look-in: ‘It’s something the industry doesn’t want to talk. Just the carbon fibres themselves are complicated enough.

'If all of a sudden we start throwing out that there are dozens of different resin systems, holy cow, now you’ve just entered a level of complexity that our industry just may not be ready or willing to accept.’

Epoxy resins certainly aren’t as sexy as lustrous black carbon fibre, which might be another reason why marketers don’t pay much attention to them.

And it’s true that a good resin will not make up for poor-quality carbon fibre – the stiffness of the frame will still depend mainly on the modulus of the carbon fibre, as Cervelo’s Matthews says: ‘Stiffness is dominated by the fibre properties; the resin stiffness has little overall effect.’  

However, resin is a subject that potential bike buyers would be wise to take an interest in, because it can be one of the deciding factors in how well a carbon fibre bike performs on the road.

Colegrove says, ‘Higher performance resins will give you better properties – you get better toughening, you can also get the fibres held better in position so you get better load transfer of those fibres so they are very strong. You want those things working for you.’

And remember Pinarello’s marketing statement for the Dogma? The ‘nanoalloy technology’ that it’s referring to is in the resin, which was developed by Toray.

Riley says, ‘Our proprietary nanoalloy resin for Pinarello has sprays of fine nanoparticles in it that help to absorb shock. It’s one area where resin can have an impact on performance.’

In a world where blinding people with science is the norm, resins offer a whole new avenue for the marketing men, so expect to hear a lot more about ‘nanoparticles’ and their ilk in the future.

Recipe for success

There can be no denying that carbon fibre is amazing stuff, and that more money buys stiffer, lighter carbon fibre held together with advanced resins. But what is obvious is that having the best materials does not guarantee the best bike.

As Riley says, ‘In the wrong hands it can have a detrimental effect on the bike’s performance. It has to be quality controlled at all times.’

The art and science of carbon bike building lies in knowing what types of carbon fibre to use, where to
place them on the frame and in what orientation.

Matthews at Cervélo says, ‘Each frame has different requirements for cost, stiffness, weight and other performance targets. We always adjust materials and design together to meet those requirements.’

At Trek, Colegrove agrees that it’s not easy to tell the quality of a bike from reading the list of ingredients or even by looking at the bike itself: ‘It’s difficult because people cannot see what the quality of the laminate is from the outside. All you can see is a pretty paint job.

'You have to rely on your opinion of the company – do you believe this company has good quality, good precision, good repeatability in their material selection, their engineering and their processing, and ask yourself, “Do I feel good about the product that I am buying from company X?”’

It means that no matter how impressive the jargon on the marketing brochure, the only way you can ever be certain of the quality of a bike is to get out there and ride it.

Until they start producing bikes in graphene - then there'll be a new lexicon of bumpf to ge to terms with.

This article first appeared on Cyclist.co.uk in April 2016

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