Carbon bikes make me nervous. Can you ease the tension?

Question

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?

Answer 1

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!

Answer 2

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.

Answer 3

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.

Answer 4

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.

Answer 5

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

Answer 6

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 :))

Answer 7

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.

Answer 8

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.

Answer 9

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.

Answer 10

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.

Answer 11

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.

Answer 12

While it is true that pros do ride carbon fiber (CF) bikes, what the world doesn't know is that they get a new bike twice a season assuming no crashes, what the world also doesn't realize is that the race bike, not the training bike, only sees around 2,500 miles in that 1/2 season time frame. For the rest of us that means every time we wear out a set of tires we would be getting a new bike!! So, yes, failure happening on the pro race circuit is reduced because the bike is not kept long enough to introduce fatigue which is why they get rid of them so as not to endanger the riders unnecessarily. The interesting thing is that I cannot find any information about any bike crashes caused by frame, fork, or wheel failure, they only report crashes involving peds or cars or slide-offs, the rest are hushed.

Now riding an average mid-price CF bike for the average person is not usually a problem, getting 10,000 miles on one is nothing, and getting 150,000 miles on one is a whole other thing. Steel (ST), and titanium (TI) are very well known to far exceed 150,000 miles with the average rider. One of my steel bikes has over 160,000 miles on it and it still rides fine.

One comment had this stuff backwards; while aluminum will dent at first, then bend, and finally break, carbon will crack at first and then break. This means with aluminum, you’ll notice the warning signs while it would be somewhat sudden with carbon (especially, if you don’t inspect your bike carefully and regularly) and even without a warning. Most damage to CF stays hidden from outside view because it delaminated or splintered, or cracked on the inside of the tube wall.

This is why CF bikes all have a weight limit, granted, most of that weight limit is in the wheels not the frame, but one frame is designed to be a tad more robust to weight than the wheels are, but not much more, maybe another 20 pounds more, so if a wheelset is rated for 220 pounds, the frame is usually rated for 240. When I bought my Lynskey, a TI bike, I rejected the Lynskey CF fork before I took possession of it because they could not tell me its weight limit, so I opted to have an Enve 2.0 fork installed instead because it was rated to be used on tandem bikes, meaning it can carry a lot more weight than 240 pounds. But I only weigh 175, so the standard fork would have been fine, but this CF stuff can be tricky stuff, so by getting a fork over-engineered, or far overrated for my weight I'm confident it should last a lifetime of average use bar any crashes.

One of the big indicators as to how weak CF bikes are is that it is REQUIRED if you are tightening any screw or bolt, nut, clamp, etc that you use a torque wrench, failure to do so could cause over-tightening, and when that happens you will crush the fibers which will eventually lead to something breaking. This might be the biggest reason why CF seat posts and CF handlebars fail, but even screwing in the bolt to mount a water bottle cage can damage the frame if it's done too tight.

CF is strong as long as it is used within it's design limits, and each bike will have different limits, the real expensive $10,000 plus CF bikes will be less durable due to the measures taken to reduce the frame weight by making thinner CF walls, then a $3,500 CF frame that will be heavier and thus thicker tube walls. Also, generic direct from China CF stuff is the worst stuff you can get, stay away from those, don't let the low prices blind you or it could kill you.

Google: How to Tell If Carbon Bike Frame is Cracked? [Answered 2022] - Cycling Revolution

Google: Why Carbon Fiber Bikes Are Failing (outsideonline.com)

Google: Cyclists falling victim to an undetected danger with their bikes | The West Australian

This guy is a well-known CF engineer and repairs CF bikes, he knows his stuff; Google:

There is a lot more out there regarding the problems with CF, what I showed is just the tip of the iceberg.

I use to have an aluminum bike, and it was a problem child, it developed a crack at the top of the headtube and radiated down from the headset, the bike manufacturer would not honor the warranty because they said it was due to fatigue and that isn't covered...fatigue? The bike was less than a year old, with less than 4,000 miles, but it would have cost me more to fight the case than just to buy a different bike.

I have several steel bikes, and a titanium bike, never had a single problem with either, even a friend of mine bought a very inexpensive Motobecane TI bike and his bike has been great since 2011, he did have to replace the fork though and got the Enve 2.0.