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4/15/12 7:05 P

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Poor maintenance is the greater cause of a lot of peoples issues, unlike pros we can't afford to put our bikes in the shop after everything long ride or crash. However if it is a serious crash or you put your bike through a lot of stress, its the cost of the sport.

Do enthusiast need a carbon bike? Probably not but that pound can make the difference going up hill and having a frame that is stiff is nice. I don't race (yet), but I ride 180 miles a week minimum and I would not ever trade my carbon for metal. Anyone that is buying a carbon frame should be aware of the dangers that carbon poses.

Either way you are more likely to get hurt by a car than by your carbon/steel frame breaking. :P

SPEEDYDOG's Photo SPEEDYDOG Posts: 2,862
4/15/12 7:57 A

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I selected a carbon frame for my mountain bike not for weight savings but for responsiveness. I cannot speak to the merits of a carbon fork versus a metal fork. I am an engineer by training and temperament. I know that the low elasticity of carbon fiber is a major advantage of the material. Of course, the very stiffness of carbon fiber means that carbon fiber can reach it's yield point with very little warning.

We have all seen spectacular crashes on pro road races. I have witnessed these high-end bikes break apart during in multi-rider pile-ups. During a race these riders can be inches apart. These bikes need to respond instantaneously to the control inputs of these elite cyclist. Stiff carbon fiber frame and forks allow for instant response.

One of the reasons I popped for the carbon frame was the quality of the other components, including better wheels, hubs, shifters, derailleurs, brakes, drop seat post and brakes. In my experience the steel bikes are entry-level and have moderate quality components. Allow bikes are a step-up and will generally have good components. To get the best factory components come on the carbon fiber bikes.

I know there are exceptions, but this frame material/quality component relationship is the norm. Does a recreational rider need a top-end racing bike? Are there limits to material life on these high-end bikes?

I am distressed that TAHOEKARIN found a crack in her bike's fork. How many other riders are out there with a carbon fork that is failing?

Thanks,

Bruce



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TAHOEKARIN's Photo TAHOEKARIN Posts: 981
4/14/12 4:56 P

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I took it to my lab that I contract with to do failure analysis (one of the perks of being a self employed engineer). After putting it in fixturing to do compression testing, it's pretty clear it's starting to grow. My head is worth the new fork.

Either way, I'm getting a steel fork. I abuse cross bikes too much to rely on carbon. And if I need a lighter bike, I can start with a few pounds off my butt lol.

The only way out is through...

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BARRONVC's Photo BARRONVC Posts: 1,893
4/14/12 1:18 P

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Have it inspected. There is a spray they can use to detect a crack. I have seen surface cracks that don't go deep. If you had an accident do it asap.

What kind of bike?

If you need a replacement look at the Alpha Carbon Tandem fork. I put one on my Specialized Roubaix commuter.

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TAHOEKARIN's Photo TAHOEKARIN Posts: 981
4/14/12 12:56 P

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It appears that my carbon fiber fork has a very fine crack when it is under torsion (ie turning the wheel when on the ground) and causes the joint/steerer to make a squeak noise.

If it hadn't been for that accident I would of looked into it later in the season.

Don't ever ignore a squeak from the front end.



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BARRONVC's Photo BARRONVC Posts: 1,893
4/14/12 12:24 P

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TAHOEKARIN

I just talked to a friend that has traveled to all the bike factories in China, and Taiwan. He is really a sharp guy and has been in the industry for many years. He said the destructive testing done on the fork is really complete and he would not worry. They do test them and there is a certification.

Then he said everything Cervelo makes breaks. They try to shave weight. They also have a really funky set up with two 6 x 1mm flat heads that would seize from sweat in the steering area. They used materials that will cause galvanic reaction. The shop always brings me those things to fix. I have to say that was one terrible design and I ended up putting heli-coils in as the thread tolerances were so bad. In the past 5 years I've seen 3 Cervelo's break that were not crashed, all Tri bikes.



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TAHOEKARIN's Photo TAHOEKARIN Posts: 981
4/13/12 3:33 P

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A carbon fork is under compression during the whole ride. It wasn't so much the fork that failed as it was the fork steerer. Complex components with multilayer materials (re: composite) has always been one that makes seasoned engineers nervous. Other parts of the bike aren't as troublesome but a fork that is asked to compress as well as torsional forces with a complex component is great, if it is engineered with a high level factor of safety (usually 7 but should be double that with composite materials). A finite element analysis on it with varying degrees would show that the slightest least material condition would create a faulty part.

My problem is most carbon, heck, all carbon fiber is being manufactured in a handful of factories in China where many quality systems may not be adhered to in order to meet quantity. Deming turned Japan around with statistical methods that made Japanese products the highly sought after production products associated with quality. China is now in the same situation however, their quality still is on the low end. Destructive physical analysis is done but you can't do that on all parts because you won't have any to sell.

In my welding science and metallurgy classes the profs said one thing in the beginning of both: rivets are the strongest bond over welding. Not the best or most practical but the strongest.

My post was just about preference. Strangely enough, my carbon fork on my cross bike was making an odd sound the last two rides, after this tragic accident, it is hung up until a new steel fork comes in. Why? My cross bike is ridden on trails that are difficult and includes rocks, logs, etc. I am also following the actions of several other people that I admire and have had the luck to train with, in that they have swapped out their carbon forks for metal. I think it's more of preference than fear mongering for me. Metal bikes still fail, but I really don't need to spend money on a lightweight bike when I can simply lose a few pounds (and need to!). Hey, if I get really good and am riding pro where I get a new carbon bike for each race? Maybe.

Although, the initial intention of the first post was if you have a Cervelo with that fork, GET IT CHECKED PLEASE PLEASE PLEASE!!!!! Pass it on!!!!

The only way out is through...

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4/13/12 12:52 P

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One of my other points is if carbon fiber is really necessary for non-competitive cyclists. The weight penalty of riding a quality steel frame vs a mainstream carbon fiber frame is about 1 lb. This is about the weight of a filled water bottle. Does your bike ride noticeably different with a full water bottle vs an empty one? Do you think if you didn't know already you would be able to tell if an opaque water bottle on your bike was empty or full based on the bike's ride? Granted that a competitive cyclist wants every advantage they can get. A 300km race may be won by centimeters and an hour time trial may be won by seconds; in cases like this even tiny improvements can mean the difference between victory and defeat. For the rest of us does that pound even matter? Does it help us enjoy cycling more? Does it somehow make our life more complete?
A road bike in addition to fitting and being durable needs to be strong, stiff and light. For cycling enthusiasts the point of diminishing returns occurs at a much lower price point than they usually shell out for a new bike.
Steel is still a great material for bicycle frames. It has a good combination of value, strength, weight, and durability. Other materials accentuate one attribute at the expense of one or more of the others. Steel is also the easiest material to customize or repair.

BARRONVC's Photo BARRONVC Posts: 1,893
4/13/12 11:44 A

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Carbon as a material is really tough. Bonding is critical but it's been around. I have an aftermarket tandem carbon fork in one of my bikes and the other is a custom fork that came with my Serotta.

Design and process is probably problem. Cervelo has had many design issues. I picked up a pro triathlete when his for cracked during a training ride. He was sponsored by Cervelo. I have not noticed a problem the road bikes like I have with the tri bikes.

Any fork can break! Even Steel if not assembled correctly. That is a huge stress area with major consequences if it breaks.

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DDOORN's Photo DDOORN Posts: 25,526
4/12/12 9:51 P

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Hmmm...have a carbon on my Specialized Tricross...but I stick pretty much to road cycling.

Such a tragedy!

Don

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4/12/12 12:25 P

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I'm very much a steel-is-real guy myself. Carbon fiber composites can be stronger, lighter, and stiffer than any metal but they can fail catastrophically. I hate to bring this up since it can be seen as fear mongering. Consumer carbon fiber is highly engineered with some non-carbon reinforcement that trades some of its strength and stiffness advantage for dependability. Well engineered carbon fiber composite parts are safe and should last longer than any cyclist would care to ride them. Poorly engineered or stupid-light carbon fiber composite parts could be dangerous though; in this case its catastrophic failure mode is rather inconvenient. Steel fails gradually. The only steel frame I ever broke creaked for months before the seat stay broke below the the top/seat/chainstay junction. I swear I went over every component on that bike a dozen times looking for the creak that turned out to be the frame. Even after the stay broke I was able to ride my bike home though it rode very squirrely.
Different steel alloys have different qualities. The strongest steels are brittle. Most steel alloys for bicycles have about 10% elongation. Elongation is the amount it can stretch before breaking and is a measure of ductility. The more ductile a steel the more likely it is to survive a crash and the more likely it can successfully straightened by cold setting (bending). Carbon fiber composite's elongation is near 0%.
From a dependability point of view titanium is the best. The most common bike alloy 3Al2.5V has elongation over 20%. The slightly stronger but much more expensive 6AL4V alloy's elongation is 10% or about that of steel. CP or commercially pure titanium is more ductile than 3Al2.5V but only half its strength. Titanium also doesn't rust and withstands salt water better than most stainless steel.
Based on mechanical qualities I should favor titanium but no titanium bike can look as sexy as a lugged steel frame so I remain a steel fan.

TAHOEKARIN's Photo TAHOEKARIN Posts: 981
4/12/12 11:02 A

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Granted there is a recall on this fork, but what a tragedy.

As an engineer, I am not a big fan of carbon fiber on something that could cause a catstrophic accident, like a fork. Cervelo has a recall on the Wolf SL fork. A local cyclist was found laying in the road with a head injury and died. I have a carbon fork on my cross bike that is getting swapped out with steel. The way I ride that thing, I just don't trust it. Maybe I'm wrong, but nothing is worse than being nervous while riding a single track on a bike whose fork might fail.

http://www.tauntongazette.com/news/x1157
746235/Cops-Bike-defect-likely-caused-
fatal-Rehoboth-crash



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