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carbon cranks meet the apex of the turn...(7 posts)

carbon cranks meet the apex of the turn...legs
Jun 7, 2002 4:39 PM
sometimes.. when i am really riding on at the end of a crit race... i scrape the ends of my cranks (i haven't hi-sided a bike since i was a kid)..
what happens if you have carbon cranks and you scrape them up..doesnt that f them up or are they built to withstand a little real world abuse?
How is that possible?PODIUMBOUNDdotCA
Jun 8, 2002 2:37 PM
How do you scrape the end of your cranks??? I can understand the outside of pedals and shoes but not cranks... hummm. But anyway in my opinion this shouldn't cause any damage as long as it wasn't to deep. Although carbon CAN be weakened by scratches at the end it shouldn't affect the physical strength of the crank. It just makes it look less pretty...

Hope this helps,
Nick Corcoran
How is that possible?legs
Jun 9, 2002 8:36 AM
i am as mystified by the scrapes on the cranks as you are...but regardless, they are there..(?????)
Say what?Kerry
Jun 8, 2002 5:35 PM
As per PODIUMBOUND, how is it that you are scraping your cranks in a race. The only time I've seen cranks scraped (most frequently on tandems) is when you go over a bump with your pedal down, riding in a straight line. And the bump would have to be something like 3.5-4" high to hit the crank IF it were all the way down. Ignoring the likelihood of what you suggest, any CF part will be weakened once you start digging into the fibers. Surface scratches MAY become stress risers for cracks in the epoxy matrix if they are deep enough. Most CF stuff has a clear coat on it, and scratches to that have virtually no effect.
re: carbon cranks meet the apex of the turn...Landsharkrider
Jun 8, 2002 7:32 PM
I bought a pair of FSA carbon cranks for my mtb a few months ago. Last weekend, I did my first race of the year and it was on a course with plenty of logs to go over.

I kept knocking them on the logs as I went over since I was trying to haul ass. Every time I did it I cringed. After the race, I checked them out and they held up pretty well so far. Only a couple of scratched.

From my understanding, they are just carbon wrapped over aluminum anyway. I guess I'll find out soon if I'm wrong.
Structural instabilityPODIUMBOUNDdotCA
Jun 8, 2002 10:49 PM
From my very limited understanding of this I think the clearcoat protects the fibers. And if the crank didn't have an aluminum pedal insert I'd be worried. But does it not distribute the load over a greater area so the area that is scratched would not be stressed more than 1 or 2% more than normal? If you think about it an aluminum crank is just as succeptible to failure with the same type of scratches if they go deep enough. Hmmm...

I hope only I'm right on this one whether its not even close to my area of expertise or not!

Nick Corcoran
Structural instabilityCarbon fiber fanatik
Jun 9, 2002 4:43 AM
On higher quality carbon fiber goodies, the outer layer of the shell is generally used for appearance purposes. The structural layers of carbon don't look or work anything like the "final" outer layer. Simple scratches will not affect the overall performance of the piece. Take for example Kestrel. I have a kestrel cs-x mountain bike. The frame is warrantied for life. That would not be possible if the integrity of the frame could be compromised by the obvious stones etc, kicked up by the front tire, smacking against the down tube.
Carbon Fiber IMHO is the ultimate material. True, it has it's downsides like any other material, but overall, it is by far the most engineered and manipulative man made material. Technology and usage are taking huge steps foward and will continue to do so. Not to mention the fact that carbon has a natural beauty that no other material has.
But then again, beauty is a personal thing and I also "skip a beat" when I see the craftsmanship of a fine fully, lugged steel bike.

Just my opinion.