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Is it only me, or do Carbon bikes make others nervous!

I realize that carbon fibre is strong, but for some reason, having a bike that isn't made out of metal seems like asking for trouble.

My main reason for not liking it is the failure mode. Carbon won't bend like metal, but rather crack and snap in half. This makes me nervous.

Think of it this way. Over time a frame develops weaknesses. In a metal frame, these weaknesses would cause things to start bending. The bending would be noticeable and I would replace the part before it caused and accident.
However carbon doesn't bend, and it will eventually just break. This would most likely cause an accident. I don't want my front fork to just snap as I'm riding down the road.

Is my concern warranted, or am I just unfamiliar with the technology? How often should carbon parts be replaced? What signs of wear should I look for?

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    Normally I'd say "Just say NO to carbon", bit I suppose it's getting hard to find a medium-quality bike without at least a carbon fork, because it's become so fashionable.
    – Daniel R Hicks
    Jul 7, 2011 at 19:38
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    You might want to take a look at the gallery of bike failures - you might be surprised at how many metal component failures occur without much warning. I'm currently nursing a bum shoulder due to total failure in a 4130 (cromoly steel) rack tube - it developed a hairline crack in a location I wasn't really able to inspect and then proceeded to fail quite suddenly. Bending is basically unknown as a fatigue failure mode for bicycle components. Post-crash, maybe, but not from cyclical loads.
    – lantius
    Jul 7, 2011 at 23:39
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    You'll also want to check out Craig Calfee's carbon whitepaper, which explains in some detail the characteristics of carbon fiber that make it suitable for bicycle design and why some manufacturing techniques using it are significantly better than others.
    – lantius
    Jul 7, 2011 at 23:41
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    @lantius - Now Kibbee will be nervous on all bikes.
    – Goodbye Stack Exchange
    Jul 8, 2011 at 4:31
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    Stay with steel, preferably lugged - fork too, it's still superior to anything.
    – user8340
    Oct 8, 2013 at 3:09

11 Answers 11

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Watch the Tour de France...you'd be hard pressed to find a bike that is not carbon. Yes pros do get multiple steeds, but remember riding is their full time job. When was the last time one of us put 30-50 hours on a bike in a given week, never mind for 6-8 months! Now think about the wattage these guys put out and hopefully you are getting the idea...that carbon is a proven material.

Do failures happen? Yes, but the frequency is so minimal and when it does occur it is not the instantaneous snap in half you fear. Furthermore, no multi-million dollar corporation would be able to mass produce a product that posed as serious of risk as you suggest.

As far as carbon forks go, I use them on the road, as well as, cross and have never had a failure. Their ability to absorb vibration is unparalleled and I honestly cannot imagine riding a bike without one. I have a stable of bikes and all have carbon except one and that one has a suspension fork. My 29er MTB has a rigid carbon fork that replaced a ti rigid a couple years ago!

Now having said that, I have been riding carbon frames on the road for 5 years and the benefits are unbelievable. I used to have a carbon mountain bike and it was phenomenal. Carbon is not the end all and be all. There are other materials that ride extremely well.

Hope that helps!

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    Aren't surface scratches more of a worry in (monocoque) carbon components?
    – James Bradbury
    Oct 8, 2013 at 8:04
  • I have ridden Ragbrai for the last 4 years on the same carbon bike. 3,000 miles total each year on that bike, and at least 35 hours in the saddle during the week of Ragbrai. I need new tires each year, but the carbon bike has no problems. I also have a 2003 Cannondale with a carbon fork and it has no problems.
    – Gary E
    Apr 24, 2015 at 16:17
  • Don't the Tour de France roads have better conditions? For someone who rides in the city for transportation, I'm sure the roads are less maintained and it's more likely that heavier loads would be carried. I feel like 40 hours a week on smooth roads may be better for the bike than 5 hours a week on less maintained roads. I could be wrong here because there are other ways that a bike frame can be stressed or protected.
    – Brian
    Jun 30, 2018 at 19:13
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    @Han-Lin this year's TDF went over the famously bad cobbles of France's Roubaix region, as does the Paris-Roubaix one day classic which occurs each year. You would be hard pressed to find a worse surface to ride over anywhere in the world, including off road riding. Despite this, every single rider in both races was on a carbon frame, and most were on carbon wheels. Similarly, carbon frames are ubiquitous in the FIS XC world cup, and in extensive (though not universal) use in Enduro racing. The only discipline where it hasn't become the dominant frame material is downhill.
    – Josh Doebbert
    Aug 11, 2018 at 17:03
  • @JoshDoebbert I still find it hard to ease my concerns because of the death of a cyclist using a carbon fork. Is galvanic corrosion a concern in the TDF? Maybe we should replace our carbon fork every few years. It's cheaper than an ambulance. cyclingtips.com/2016/12/…
    – Brian
    Aug 15, 2018 at 6:03
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Carbon fiber is stronger, and far less susceptible to fatigue than any other frame material on the market. It can be engineered to have the strength of titanium, the ride quality of steel, and the stiff and powerful performance of aluminum at the same time.

I have only broken 2 frames in my life. Both were aluminum, ridden far beyond the fatigue life of the metal. I have seen carbon break, but usually it is in a major accident. A car crash or something similar.

If a carbon frame cracks from fatigue, it shows small crack in the paint, then splintering, and then it will look like crushed bamboo when it fails fully. The frame will last longer, and you will have more warning of failure on carbon than any other material.

As for why you should choose it, it makes your ride more comfortable, more stable, and more pleasant. It's also lighter, but that is at best a secondary reason.

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  • I always thought that carbon was stronger but only to a point.
    – Goodbye Stack Exchange
    Jul 8, 2011 at 4:33
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    @Neil, that's true. But that point is based on the engineering of the frame, and it's basic construction. In our shop, we have a carbon tubing cross section cut from a frame for demo purposes. It is a round tube, 2mm wide. It looks like a keyring made of carbon. I can place that ring in a vice and compress it to an oval 1/3 of its width, and it will return to its original shape. No other material except ti will do that. And it will do it over and over again. Push it too far, it will break, yes. But that point is well beyond what would have already destroyed a different material frame.
    – zenbike
    Jul 8, 2011 at 6:25
  • Ti will do the same thing, but the fatigue life is shorter, and compression point for permanent damage is lower, so it lasts less time.
    – zenbike
    Jul 8, 2011 at 6:27
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    Trek gives lifetime warranty to most frames and 2-year for carbon ones. Why? link
    – Vorac
    Nov 5, 2013 at 14:56
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    @Vorac: That is not accurate. They have a limited 2 year warranty on the Session (carbon) model frames and swing arms. All of their other carbon frames have a lifetime warranty. As to why, you'd need to ask Trek. But I suspect it has something to do with the way the Session is ridden. Being a freeride/DH machine, it's use is far outside "normal". By the way, the Aluminum Session listed has a 3 year warranty, not lifetime.
    – zenbike
    Jun 6, 2014 at 15:23
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Carbon fiber often stands up to higher stresses than comparable aluminum or steel frames. You really have nothing to be worried about as long as you are buying from a reputable manufacturer.

Check out this video for more info: Santa Cruz tests carbon vs aluminum frames

You'll notice that aluminum fails under much less stress than carbon does in almost every single test.

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  • Yes it is true.. After crushing three specialized Enduros, two Other aluminum frames over the last ten yrs, i have yet to break my white Santa Cruz Carbon Blur LT to this day after over a year and a half... 6,000 miles of trail riding... i am sold on Carbon, and Santa Cruz Bikes does the trick on this end. I also own an old 1989 Kestrel EMS carbon road bike, that i like to take on fireroads in the mountains and on paved roads with lots of DH, potholes, hazards, from the summit to the coast, and after many years of abuse and thousands of miles, not problems at all...
    – sov
    Jul 21, 2014 at 7:51
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From my understanding, carbon fiber is extremely strong within its designed load parameters. That means the directionality of the load, the amount of load, etc. It is only when one goes outside this load design that you start to see failures (other than manufacturing flaws, but that could happen on any bike).

For example, clamping a carbon fiber handlebar using a stem designed for steel/aluminum. The style of clamp is wrong, and can lead to crushing the bar at the clamp. Same applies for almost all clamping surfaces. Most components are not designed to be clamped down on unevenly.

As for the frame and fork, as long as you don't run into a wall, for example, you are probably going to be fine. Doing so would put stress on the fork in the wrong way, plus try to pull the head tube away from the top tube, a stress it is not intended to handle.

Now, to fully disclose: I weigh 375lbs. Carbon fiber bicycles are NOT designed for my weight, and quite frankly that scares the crap out of me. As a result, I ride Surly bikes. Chromoly Steel with high spoke-count wheels to feel safe.

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    This is kind of my point. I don't ride in a velodrome. Hitting a deep pothole could cause pressure in the wrong direction on the fork. Also, I'm not sponsored, I want to know if I would have to replace components more often.
    – Kibbee
    Jul 7, 2011 at 20:26
  • I've known a couple of guys who ran into parked cars and bent their forks. There you at least know the bike's been seriously damaged (especially when the front tire rubs against the down tube), but it would be hard to tell when a carbon fork's been over-stressed.
    – Daniel R Hicks
    Jul 7, 2011 at 21:50
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    If I needed to save weight that badly I'd go on a diet.
    – Daniel R Hicks
    Jul 7, 2011 at 22:55
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    Riding carbon is not about weight. It's about comfort and performance. @Daniel, carbon forks show their damage, just in different ways. Usually as cracking in the clearcoat over the material. It also takes a much higher impact to do damage. Have you owned/ridden a carbon frame in the last 10 years?
    – zenbike
    Jul 8, 2011 at 6:28
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    @Kibbee: I've ridden my carbon bike into a curb at 40kph. Not recommended, btw. But what broke was not the frame or fork. It was the wheel, which is generally the part of a bike with the least tolerance built into its engineering, and generally not carbon. I understand the apprehension, but most of the horror stories you hear about carbon frames breaking catastrophically are (a)Left over fro
    – zenbike
    Jul 8, 2011 at 6:37
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I disagree with your assertion that a metal bike is better because gives you warning
It is not common that you see a slight bend prior to total failure.
And a sight bend will typically result in injury also
If the fork bends and traps the wheel on the frame you are going down

Brittle failure is when it snaps and plastic deformation is when it bends.

Metals can also suffer from brittle failure - especially aluminum
A high carbon steel (designed for hardness over strength) can have brittle failure
With loading metals fatigue and often with no visual indicator

Titanium is the least brittle followed by steel then aluminum
Titanium is also expensive

Correct a 3 lb carbon frame is not as strong as 6 lb steel frame
But 6 lb steel is not twice a strong

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After traumatically sudden failures of a carbon seatpost, and shortly after, a carbon wheel, both resulting into painful crashes, I decided that my next fancy bike would not be a carbon fibre one, but titanium. I ended up buying a Cube HPT (frame made by Lynskey). After two years of moderate use (no crashes) I discovered a horizontal crack across the weld on the top of the seat-tube. When I asked my dealer about possible repair, they looked the frame over more closely, only to discover 3 (three!) more long cracks on the horizontal stays. That was the end of it. I suppose at least it didn't suddenly fail causing injuries but not exactly impressive either. I also own a Van Nicholas Tuareg ti-frame (MTB) which makes incurable creaky noises under load. The bike had been completely rebuilt twice (new transmission bits, looking very closely at correctly torqueing up everything), before discovering it was actually the frame making the noise, even though no cracks are visible. I now understand that creaky noises are not entirely uncommon on Ti frames. I also managed to break the top clamp of a Ti seat-post (Van Nicholas) - again, another "slow" and injury free failure, but enough to end my interest in titanium for good, even though I still love the looks. Cube has now kindly sent me a HPC Litening frame to replace the HPT (which is no longer made), free of charge. That frame is made of carbon. I am not sure whether to give that a try, or flog the carbon frame on eBay, and carry on using my steel and alu bikes instead... BTW - I weigh in at about 95 kg and reasonably strong (but no threat to the likes of Mario Cipollini though :))

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My experience with steel frames is they can fail suddenly and completely. That said I've only seen two frame breaks and one caused no injury because the bicycle held together enough to not throw me on the ground. The other steel failure was a too light experimental racing MTB in the early 1980's that completely broke apart throwing the rider onto the ground at a MTB race I was in. I've been reading as much as I can about Carbon bicycle frame/fork failures. They seem to experience this at a higher rate than steel frames and forks. There are lawsuits now going through the U.S. court system and Australian courts trying to address this situation. Because of the way steel pipe is manufactured there is almost no way to have air pockets within the steel. Carbon manufacturing relies on various methods to clamp the curing material but pockets of air can be trapped despite their best efforts and this can lead to frame/fork failure. There are other reasons for Carbon failure and I believe, in the future, we may see a much more rigorous testing of carbon components. By this I mean x ray and possibly other non invasive testing techniques. Carbon is being very successfully used in passenger and military aircraft but they are subject to complete teardown inspections every couple of years and preflight inspection before every flight. Bicycles tend to be used with minimal inspection. I ride steel bicycles because of the proven durability and the availability of so many good used frames and forks for builds at such good prices. As you can guess I don't race anymore.

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  • Yep, steel frames can and do break. But most important for steel frame failure modes is geometry: With a diamond frame, it's rather hard to get a full rapid disassembly into two pieces - you always have a second tube to save your butt. Even better if you have one of those rare bikes that have additional tubes going straight from rear dropouts to headset. Y-frames, on the other hand, just give me the creeps even thinking about how they must fail...
    – cmaster - reinstate monica
    Mar 2, 2019 at 0:19
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Aluminum will fail much faster than carbon and with less warning. It can develop micro-fracture from fatigue and then fail suddenly (I've had thus happen).

Carbon failures are more noticeable starting with cracks and developing into soft regions that splinter apart. Because the failure is occurring to individual fibers it takes a little more time.

There is no argument that steel bikes are the most durable and the easiest to repair, but there are a few American companies popping up that can repair broken or failing carbon fairly cheaply.

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There are a lot of good answers here. All I will add is I have over 10,000 miles on my carbon Felt with no problem. It still looks and feels like new. I would buy another carbon frame without hesitation.

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  • 10,000 miles is nothing for a good frame. That's what I expect even the cheapest components to last.
    – cmaster - reinstate monica
    Mar 2, 2019 at 0:21
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Carbon bikes make me nervous too because they can look intact and still fail catastrophically. For metal frames, dents can give it away. There's news about carbon bike failures even causing a death. In both accidents, they were catastrophic. One was at 5 km/h and the other at 35 km/h. https://thewest.com.au/news/wa/cyclists-falling-victim-to-an-undetected-danger-with-their-bikes-ng-b88329369z

According to the article, carbon bikes can fail without warning even when maintained and examined regularly.

Pro cyclists may ride full time but have different conditions compared to us recreational and commuting cyclists. That means estimating its lifespan by hours may be inconsistent. Roads that allow 20 minutes of uninterrupted intervals may have less braking, acceleration, bumps, etc. If they have rain bikes, their carbon bikes can be protected from scratches from debris thrown by their wheels on wet roads. Their pedalling styles may be different too like coasting percentage and cadence.

There are some good bikes that I stopped considering just because they had carbon forks. It's more common for 10 and 11 speed bikes to have carbon parts. If the bikes are sold with carbon parts, we can still try asking if they can substitute it with another material.

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I was looking at mountain bikes and feeling similar qualms, so I can't promise that road bikes will be quite as overdesigned. Wait til the end for the official Pinkbike "swing-a-carbon-frame-into-a-concrete-block" test.

To that end, I have personally tried to smash a 1992 trek OCLV about a year ago (at that point 23 years old and pretty much abandoned at the shop I worked at) by applying the "swing-a-carbon-frame-into-a-concrete-block" test and it was by no means an easy task. yes, older carbon frames were probably more overdesigned than newer ones.

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