Opinion: When it comes to carbon bicycle frames, durability should also be a performance metric

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I recently wrote an article discussing some of the new technologies that have been proposed to help improve the damage tolerance of carbon fiber frames, forks, and components.

On the one hand, so-called hybrid composites — made of a mix of carbon, plastic, and steel fibers — help carbon composite structures mimic metals by deforming in a severe impact instead of coming apart entirely, creating a sort of “safety cage” to help hold everything together. Meanwhile, newer thermoplastic resins claim to directly boost the impact resistance of carbon composites so they can handle bigger hits without permanent damage.

All of those technologies sound appealing for one reason or another, but the fact of the matter is that there have always been solutions to the all-too-common issue of carbon fiber parts that can’t handle impacts.

The problem is that no one wants these solutions — or at least, they aren’t conditioned to consider them.

The cutting edge vs. pragmatism

All of these new approaches toward improving the impact durability and toughness of carbon-fiber bicycles and components seem promising, and all of them claim to offer designers and engineers the ability to maintain the ultra-high levels of performance currently available in conventional composites.

That’s all well and good, but another option — albeit, one less appealing from a marketing standpoint — already exists.

Preston Sandusky, a frame engineer at Ibis Bicycles, spent more than 20 years at carbon frame pioneer Kestrel in addition to several positions working with composites in the aerospace industry. In his opinion, the solution to the problem of carbon-fiber failure is more a matter of more closely matching the product to its real-world usage.

As an engineer, Sandusky is understandably more interested in how well a product meets its design goals, rather than how it comes across on paper. In his view, companies should primarily concentrate on preventing failure in the first place. Carbon fiber may tend to fail in brittle fashion, but it’s also immensely strong. Rather than try to alter the failure mode (which is an inherent characteristic of the material), the structures could instead just be made stronger so that that failure mode simply doesn’t come into play.

“It’s nice to prevent something from failing completely catastrophically, but I just think that a lot of times, it’s a bit of a band-aid,” Sandusky told me. “Just make sure it’s strong enough to take all of the reasonable riding and crashing and impact scenarios, make sure the structure passes that stuff first. And then, if you want to put in some Kevlar, Innegra, or something to make it even better, that’s good. But don’t make something that’s so light that it isn’t as strong as it should be for all scenarios and then add some toughening material just to hold it together.”

Sandusky feels the bike industry has created unrealistic consumer expectations. With so much attention paid to keeping weight — how many product names end with “SL” ? — more practical aspects such as durability have fallen by the wayside, only to crop up in internet forums later on when there’s an unexpected problem.

“I just don’t really buy that the impact [damage susceptibility] is worse on composite frames,” Sandusky said bluntly. “If you don’t want your bike to get damaged in a crash, don’t buy a 650g frame. An 800g frame is going to be a lot tougher in most cases, and a 1,000g frame is going to be way tougher just because it’s thicker. If someone wants a really light frame, that’s fine, but they need to be prepared for what they’re getting. Do you want it to be tougher, or do you want it to be lighter?”

What you need vs. what you want

I fondly recall my first carbon-fiber road bike like it was yesterday. That 1993 Trek 5200 was one of the earliest mass-produced, full-carbon frames on the market, and the claimed weight was around 1,100g (2.4lb) — an astonishing figure for the day, and still a respectable number more than two decades later. Progress being what it is, Trek’s lightest road frame now comes in about 400g lighter — a staggering 36% decrease on a structure that was already very light. Other brands have seen similar improvements at the scale over the years.

Thankfully, the industry has mostly moved past the full-blown weight-weenie wars, and on to other metrics such as aerodynamic efficiency. But all other things being equal, there are still few people who would choose a heavier bike over a lighter one. Weight may not be everything, but in a sport where power-to-weight ratios reign supreme, it’s always a consideration.

Our buying decisions — and the way that the cycling industry hones its messaging — are often based on the promise of performance. The problem with Sandusky’s straightforward approach is that it flies in the face of what people have been hearing for years: lighter is faster, stiffer is faster, more aerodynamic is faster, and faster is better.

But more durable? That’s not particularly interesting, at least according to the marketing folks. And it should, perhaps, also be said that the industry doesn’t exactly benefit from making frames last longer than necessary. That’s not to say that manufacturers are intentionally designing their bikes to eventually break. Product failures never cast favorable light on a brand, no matter the circumstances. But nevertheless, there is no better way to foster the purchase of a new bike than the failure of an old one.

The reality is that small improvements in performance are only truly significant for a tiny subset of the cycling population. Riding the same bikes as the pros is fun — I love high-performance bikes as much as anyone — but how we finish on the weekend bunch ride ultimately doesn’t affect our ability to pay the mortgage. Whether our bikes can survive to live another day is another matter entirely, however, and one that hits much closer to home.

For sure, new carbon bikes are generally lighter than that old 5200, and also more fun to ride since they’re stiffer and livelier than that old wooden-feeling dinosaur. Yet I have no way to make a fair comparison in terms of impact durability since there’s no public data available.

In our never-ending quest to go faster and further, what value, then, should be placed on durability? And if that aspect were measured and marketed as prominently as weight and stiffness, would it change what you ride? Would you, perhaps, choose a heavier bike with thicker tube walls and a less-lively feel, if you knew it would last an extra two seasons?

Sandusky is right that we should have realistic expectations in terms of how a bike performs. The problem, however, is that while we are inundated with figures regarding stuff like stiffness, weight, and aerodynamic drag, we aren’t provided with durability information on which we can make an informed decision. Perhaps it’s time for that to change.

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