Impact damage is a carbon fiber bicycle frame's worst enemy. That being said, there's quite a few products available on the market designed to protect carbon fiber and minimize any damage should the inevitable impact occur.
Carbon, unlike various metals, does not have a known stress limit or provide clear signs of impending failure. Carbon can and if damaged, will, fail without notice. The best way to protect yourself, because having your frame, forks, or rims fail while you are riding is potentially deadly, is to regularly check your bike for impact damage and to use some sort of impact protection in the areas most prone to damage.
The biggest cause of frame damage on carbon road bikes is ironically from the down bars swinging around and hitting the upper frame tube. From there both carbon mountain bikes and road bikes are at risk from damage caused by the tires spitting little rocks and road/trail debris into the seat stays, chain stays, down tubes and forks.
There are a few types of protection products on the market. The first is applied like a sticker and consists of a self-healing polymer skin, much like the type used to protect cell phone screens.
The other is a spray-on product that also is self-healing. I used an automotive product by Armor All - designed to protect automotive parts from impact damage and scratches. Applied through an aerosol spray can (like the type used for spray paints), this product is called "CUSTOM SHIELD".
Custom Shield is designed to spray onto plastic, metal, and rubber parts. It is 100% safe for finished carbon fiber - if your bike has a paint scheme in either matte or gloss finish, it'll be fine to use.
It applies wet but quickly dries to form a "skin" layer over the item being protected. To remove it, simply find an edge and roll the product back away from the edge and then peel it off.
It is supposed to last for up to three (3) months.
It costs $15.99/can - one can will provide 2 - 3 full coats over an entire bike frame.
*** I purchased the can used for this product test from Pep Boys Automotive Parts - it was on sale and I paid $7.99 US.
It works. Since applying the Custom Shield protective skin my bike has taken several hits from rocks and ONE hit from an unknown object - I assume it was a rock or a bolt or nut of some sort.
In each instance where my frame was struck, the skin was marred or damaged in some noticeable way. This has provided me a clear "map" of where my frame needs the most protection.
It is easy to apply, but I'd recommend using a respirator/breather, nitrile gloves, and a well-ventilated area when applying. You will also want to ensure you do NOT touch the frame until the application is completely dry. Image 2 of this card is of me holding the product up, preparing to apply it. Note I wore eye protection, a respirator, and gloves.
It's practically invisible, although it has a distinct texture and will make your bike appear "glossy" if it is a matte finish. Images 3 and 4 of this card show the product after it has dried. There is a glossy "orange peel" texture to it.
It is water proof and dirt does not stick to it. Oils and grease however will, but will wipe off easily with a wet sponge - see cons for "being careful while cleaning".
It is affordable - but depending on how often you ride, the 3 months stated by Armor All for its life expectancy may be a stretch, especially if you are a mountain biker or trail rider.
Requires a fair amount of prep to properly coat the frame. This means it takes a dedicated cyclist to want to remove most of their bike's hardware to get the frame "naked" for application.
When cleaning, you must be very careful not to dig in too hard or you will easily tear the skin. Image 6 of this card shows what happens if you rub too hard to remove an oil or grease stain. This is what this product looks like if you tear it.
Once the skin is torn, it will start to peel and the tear will only become larger. At this point the only option is to reapply. *** Because this skin is self-healing - to a point - once it is in it's liquid form applying a new layer to heal a damaged one is easy to do.
It is a protective layer but does not disperse impact energy as some of the layered "peel and apply" skins are. Likewise, the peel and apply skins require you cut them to shape and they are quite thick. This applies easily, in wet form, and is relatively thin.
It has proven to tear easily with a strong impact or with forceful rubbing (to clean grease off of it). Image 5 of this card is a mark left from the impact of some unknown item... I heard the frame get hit but didn't see what had done it. I assume it was a rock. The frame WAS protected, but the skin tore.
Images 7-9 are places where the product is simply wearing off on it's own. The chain stay areas make a lot of sense to me for they are constantly hit with small dirt and sand particles from the chain.
BOTTOM LINE :
For light use or application in areas of your bike where you expect there to be less risk of impact, this product is ideal.
For heavy use and situations where you expect regular impacts with rocks, etc... I'd recommend one of the peel and stick solutions.
I'll be testing the peel and stick product called "Shelter" by Effetto Marioposa next.
I hope this was helpful! Have a great ride!