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Old May 29th 17, 11:54 PM posted to rec.bicycles.tech
JBeattie
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Default Carbon Bikes and Quality Control

On Monday, May 29, 2017 at 8:40:18 AM UTC-7, wrote:
Quality control for metal bikes is relatively easy - especially for steel since all of the important connection can be seen on the workmanship.

But carbon fiber bikes are another matter. No matter how well the factory is trying to make no errors these can be made. And once made they are almost invisible.

John seems to want to argue that you can get crystal clear epoxies with viscosities down to 200 when my source says that they are limited to 1200 to 1600. This makes little difference since these particular epoxies are usually only used on the surface layer of the frames for purely decorative effect.

But those are the last layers laid on the inflatable bladder that is used for the inside mold of a one piece frame or fork.

The inside layers are the sources of danger. High end bikes use many very thin layers and the lay-up is completed as rapidly as possible. A bubble can be caught or a section of cloth may not be properly wetted. This makes an area where movement between the layers can begin and this can break down the surrounding resins.

Now my experience has shown me that CF is not reliable. But companies whose engineers I respect and my own research have shown that carbon fiber without any errors in construction can be much stronger and lighter than steel and have as long if not longer life.

So what we need is more information on the percentages of CF bikes that are having quality control problems.

And you can bet that the companies that make these bikes are going to remain tight lipped on this even if only one bike in a thousand have quality issues.

Question - are the pro level bikes that are breaking so often custom built in their company's racing labs so that the quality control is much lower than the assembly lines in China or Taiwan? If so with increasing familiarity with the material we can expect the racing teams to have progressively less trouble with their mounts.

Once constructed there is almost no way of detecting fatal flaws in the construction and that is a bonus for the American legal system in which a broken fingernail can end in a million dollar settlement.

So until we have tort reform we have little way of knowing just how safe a carbon fiber frame and fork are.

So you make your choice and you take your chances. And please don't hire a lawyer the day you buy a new super-light bike.


I don't get your point about the American legal system, tort reform and knowing whether CFRP frames/forks are safe. People break forks and sue. I've defended those cases. Failures are also reported to the CPSC and may result in a recall. Go to the CPSC website and search for "bicycle fork." There is also a CPSC requirement for fork strength, but it's pretty minimal. ISO/CEN/ASTM have more rigorous standards. Again, this does not mean every fork that comes off the line is flawless.

-- Jay Beattie.

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