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I have carbon cranks (SRAM S-2200) on a new bike. The side is quite protected but the bottom part, where the pedals are fitted, is not. Hitting rocks on the bumpy road is sometimes inevitable.

How vulnerable it is? What kind of damage should be considered as critical? What about single scratches when getting cummulated?

Should I care to guard it somehow? How?

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2 Answers 2

Assuming that you'll never land from a jump with your pedal down on a rock, then there is not problem.

On the other hand a little protection doesn't hurt. Maybe you can get those end plugs from CrankSkins. My race face sixc cranks had similar ends on. After riding hard for 1.5 years there aren't any serious dents and dints on them, but again, more protection does not hurt.

A more sensitive area though is that one bellow your feet (when riding a trail with your feet level). These are not protected by default (in my sixc at least) so I've taped a slice of inner tube using a strong double sided 3M tape at the correct places (keeping in mind that I always ride right foot forward).

Scratches are not a problem I think. What can be problematic is hitting rocks with the cranks. I don't have experience cracking one though.

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So you consider scratches caused by pedaling towards high rocks (not landing from jump) safe? I was suprised how easy it is to cause a visible scratch (comparing to alloy) even on the first ride. –  myneur Sep 18 '13 at 11:22
    
Sorry, you are right. I generally don't pedal a lot upwards on trails so I have not experience on that. When I do though I tend to only hit the pedals. So, in your case those special end plugs will definitely be useful. –  cherouvim Sep 18 '13 at 11:31
    
I looked at those and wonder why anyone would put condoms on the end of their cranks. From a design and style perspective they are pretty grim..... At least scratches give street cred..... They won't protect from structural damage .... –  mattnz Sep 18 '13 at 21:39
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Carbon fiber is a tougher material than you may think. For a carbon crankarm it's going to be thick throughout the arm and likely solid at the end as well as being reinforced by the aluminum pedal spindle insert. It will show scratches, but so will an aluminum crankset. It's nothing to worry about. If the manufacturer was concerned they wouldn't manufacture them for mountain biking.

Another fact you may not know is that many carbon mtb cranks aren't all carbon. Many are carbon wrapped aluminum. This is typically done for aesthetic purposes, not structural. A perfect example is the XX crankset. If you could view a cutaway of this crank you'd see that the core is aluminum with a thin veneer of carbon over top.

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