Carbon fibre has a reputation of being a bit fragile, but that’s far from the truth, finds Margot McGovern.
Picture courtesy of Paint My Bike
Carbon fibre frames and components were once the preserve of super-expensive high-end road bikes, but with improved manufacturing techniques they now dominates the road bike market, while becoming increasingly common in mountain bikes.
Made from a weave of carbon strands set within a hard epoxy resin, carbon fibre is very light and strong, can be crafted in very aerodynamic shapes, and as a frame material, is reasonably stiff, making it ideal for fast road bikes.
There have been concerns over the years about carbon fibre’s poor impact resistance, but improvements in the weave and epoxy, and the ability of designers to build in strength in frame areas where it is needed most, mean it can now be built to make downhill mountain bikes that are very impact resistant.
But some frames can still be susceptible to damage when crashed or dropped, and if you choose a carbon fibre bike, it’s important to know what will and won’t cause damage, and to understand your options if your bike is in need of repair.
Going the distance
Carbon fibre bikes can theoretically last a lifetime. A solid block of carbon fibre is practically indestructible, which is why it is commonly used in the construction of Formula One cars, aircraft and spaceships. But carbon fibre can fatigue, and the rate at which it does so depends on a number of factors, including its particular structural design, tube thickness, what kind of riding it used for and how it is cared for.
Road racer Ben Douglas told Ride On the common understanding among competitive riders is that after two years averaging 20-25,000km per annum racing and training, a carbon fibre bike will lose some of its stiffness due to the epoxy resin softening. It makes the bike less suitable for high-end racing, but still more than adequate as a road bike.
Keep it clean
Because of carbon fibre’s reputation for low impact resistance, riders often assume it’s a delicate material and are concerned about damaging their bike with harsh cleaning products.
However, unlike steel and aluminium, carbon fibre is a relatively inert material and not susceptible to corrosion or salt damage, and it is unlikely to be affected by any standard bike cleaning products.
However, bikes aren’t purely constructed from carbon fibre, as the material cannot be moulded to make threads. Therefore, parts of the bike (for instance, the bottom bracket) must contain metal (usually aluminium) and for this reason riders should avoid cleaning products containing strong solvents that may rust or corrode metal or damage paintwork.
Potential damage
Picture courtesy of Paint My Bike
Carbon fibre bikes may be chemically resistant, but like most bikes, they can be damaged. Bikes of all materials are subject to minor manufacturing defects, and Vince Attree, owner of St Kilda Cycles, says bent dropouts and snapped drink bottle cage lugs are among the most common problems he sees in carbon fibre frames. Fortunately, these problems are typically covered under the lifetime warranty provided by most major brands.
Although not all agree, carbon fibre has a reputation for being more susceptible to collision damage than metal bikes, particularly as a result of being dropped or scraped against a hard surface.
“If the paint is chipped and you can see a crack in the matrix of the carbon, or if you push on a scratched or scraped area and it makes any kind of noise, you definitely need to have it checked out,” Vince says. “Minor scratches in the paint or clear coat over the carbon fibre aren’t too much of a concern, but if it’s exposing the carbon fibre, be aware it is now unprotected and more susceptible to damage.”
A breach in the carbon weave can lead to a break in the frame, with bent or snapped rear derailleur hangers and/or cracked or shattered seat and chain stays often the result, but one of the most commonly reported issues is a cracked seat post, usually as a result of over tightening of the seat post clamp.
Riders using car racks that clamp the top tube should also be wary of over tightening the clamps.
Retailers and repairers agree that major damage is very rarely the result of a manufacturing flaw (and on occasions when it is, the affected model will usually be recalled) and it’s almost impossible for a bike to break or shatter of its own accord.
Contrary to popular belief, UV rays will not damage carbon fibre; most resins used in carbon fibre production these days contain UV stabilisers.
Damage control
Frame damage can be difficult to detect, as the paintwork can mask cracks and fractures. It is also advisable to take a cautious approach when buying second-hand carbon fibre bikes; it can be difficult to assess a bike’s condition or to judge the quality of any repairs that have been made.
If your bike has been involved in a major crash, you might consider having it checked by a bike mechanic, as additional stress placed on a damaged area may result in a major breakage.
Carbon Bike Repair in Melbourne offers an ultrasound inspection which will highlight any internal damage you might not be aware of, at a cost of $210 for the frame or $280 for the frame and fork. Quantum Bicycles in Western Australia offer a UV inspection, which also highlights internal damage, for a cost typically of between $88 and $145.
Alternatively, as with any bike, it’s a good idea to check for visible cracks, scratches and scrapes when cleaning, get it serviced regularly (every four to six months) and seek a mechanic’s advice if you notice any unexplained creaks or noises, or are concerned about potential problems.
Repair
Picture courtesy of Paint My Bike
If your carbon-fibre frame has been damaged, the good news is that in most cases, it can be repaired.
Confident DIY gurus might be tempted to try their own repairs, and there are plenty of websites and YouTube videos that provide instructions, but for most this isn’t a sensible option, as if not executed correctly, the frame can incur greater damage.
Some bike shops undertake minor repairs, such as regluing snapped water bottle cage lugs, but Vince says he sends anything more severe to a specialist carbon fibre repairer.
Finding a reputable repairer can be difficult, and it’s wise to do some research before deciding who to use. Many carbon fibre repairers have recently been forced to close for failing to meet insurance requirements. Consequently, you may have to send your bike interstate, and there can be lengthy waiting lists; sometimes as long as six to eight weeks. The good news is that good repairers have a reputation for returning bikes as strong or stronger than their original condition.
Repair or replace?
Carbon fibre as a material is relatively cheap, but due to the skill level required to work with it, and the cost of retouching the paintwork, repairs can be expensive.
The exact cost will depend on the bike’s design and the extent of the damage. A small repair, for example a crack around the seat tube, may cost $200, while major damage, such as a destroyed chain stay, might cost $800.
Most repairs average between $400 and $600, which includes paintwork, and, according to Brad Prescott of Turramurra Cyclery, the work will typically take between one and three weeks, as the repair process must be completed in stages, with the resin requiring time to set and the paintwork often taking many hours.
Alternatively, a damaged part can be replaced. According to Vince, bike shop prices for a new carbon fork start at around $350 and frames at $1,500. Even a small part, such as a seat tube, can cost $200. So whether you choose to use a repairer or replace the part is likely to depend on the cost of the repair relative to the replacement part and the time necessary for the repair versus the time to source the part.
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“the common understanding among competitive riders is that after two years averaging 20-25,000km per annum racing and training, a carbon fibre bike will lose some of its stiffness due to the epoxy resin softening.”
What?! The same ‘common understanding’ was used to say that metal frames ‘went off’ after a couple of years. They don’t. Metal frames don’t get soft or go off after a couple of years of racing. The loads placed on frames are well within the capacity of the metal to deal with and will not result in fatigue. Scientific testing over the years has proved this again and again.
I dare say the same applies to high end carbon frames. That aside how do you juxtapose the above statement with the claim that carbon fibre is ‘relatively inert’ is it soft after two years or inert? And the idea that carbon is somehow more inert than steel and aluninium is just silly. Yes, if I take my metal frame surfing and don’t wash it off, it will quickly deteriorate but the practical reality is that even a casually cared for metal frame will last a lifetime and is unlikely to corrode to the point of risk of failure. Let alone a well cared for stainless or titanium frame which will probably be in the same condition in a millenium if looked after.
Repeating these kinds of silly myths really detracts from the usefullness of this kind of article and calls into question the factual basis for all the other claims made therein.
I’ve broken/cracked two aluminum frames in 15 years of weekend warrioring so I’d say aluminum does degrade and certainly doesn’t last a millenium. Wish’d it did but I’ve got the proof of two beautiful, practically useless frames hanging on my wall that say otherwise. It makes since to me that epoxy, like any glue will degrade as everything does over time that is exposed to friction. I’ve recently purchased a carbon frame and I’m worried having seen chipped paint and exposed carbon. The ride is amazing. However, it seems the care for it will be more labor intensive and worrisome, though totally worth it.
Yes, I understand this is a necropost, but being that I found this thread in a Google search today, I think it’s reasonale to reply.
Both aluminum, and steels do “wear out.” This is neither speculation, nor myth. The property which describes how long it takes for a material to fail under purely elastic loading is called fatigue strength. Now, steels do have a stress limit below which no number of loading cycles will cause the material to fail, but aluminum, and its alloys do not.
Yield strength describes the greatest stress which can be applied while deforming a material only elastically. The yield strength of Reynolds 853 steel, and 6000-series T6 aluminums are 130ksi, and 35ksi, respectively.
Let’s assume that a rider is capable of applying the same stress to an aluminum frame as he can to a steel frame. Let’s also assume that the rider is incapable of plastically (permanently) deforming either frame. These assumptions imply that the rider applies a maximum stress of 35ksi. Lastly, we assume that the frames are isotropic, and free of flaws. Under this 35ksi loading, the aluminum frame will fail after 65,000 cycles. The steel frame will fail after 200,000 cycles. Now let’s say that the rider can only apply half of the yield stress of aluminum to the frames. The aluminum frame will fail after 50,000,000 cycles, while the steel frame will not fail.
Ref:
https://upload.wikimedia.org/wikipedia/commons/3/30/S-N_curves.PNG
http://torusbicycles.co.uk/materials
https://en.wikipedia.org/wiki/Fatigue_limit
Excellent excellent answer.
Please be aware when attempting to get an ultrasound examination to assess your carbon frame after a crash- i had a poor experience with Leuscher Technik: i brought my bike in to them (a 1 hour return trip) AFTER being told to “bring my bike in”, that the cost was “$290” for frame and fork inspection and that it’d take “a couple of days” for a report.
FIVE business days later, i got an email saying it’ll actually cost $520 because they only wanted the frame and not the whole bike and clearly, it was going to take more than a couple of days – why didnt they tell me that when I rang them? I received no answer to that.
Their unprofessional service (how hard is it?) left me with no confidence in their work.
I did not proceed with the inspection and have since bought a new frame.
Carbon fieber is expensive and fragile, aluminium is cheaper, little more weight, but more firm.
Minor point, and I don’t have any expertise in bikes (but do in boats):
“carbon fibre is a relatively inert material and not susceptible to corrosion or salt damage”
True enough, but carbon fibre is actually remarkably active electro-chemically, and will cause quite rapid corrosion of some metals it comes into contact with (if there’s moisture around).