Wow, 203 mm rotor on a city bike?  I use a 160 for cross county and rough trails, and never thought I needed more braking power (more skill, maybe:)).  I also wonder if the fork would have held up with a smaller rotor.

So you switched from single speed to the derailleur?  How did the weight change?  I never seriously considered a single speed, but was curious on how much weight it would drop.

Again, I'm no expert in composite failure modes, but nothing I've seen would stop me from riding my Chiner frame.  There is a lot of info out on the web, but it can be tough to sift through and find anything relevant.  It may be describing a completely different process than making bike frames, but this paper has a few pictures of broken test bars- http://www.scielo.br/scielo.php?pid=S1516-14392005000100016&script=sci_arttext  - the loading method has a big influence on what the fracture looks like as well as the layup. Particularly interesting (to me, anyway) was the conclusion-
"In general, the flexural and shear tests showed that the matrix type caused greater influence on the mechanical properties than the carbon fabric arrangement type. The F584/PW and F584/8HS laminates showed the highest flexural strength values than the F155 epoxy ones. This behavior is attributed to the higher toughness of the F584 matrix, which was modified with a thermoplastic"

Which makes sense, since the fiber is so much stronger than the matrix the overall strength depends on how well it holds together.  I guess instead of talking about the carbon fiber the bike companies should talk about their new toughened epoxy resin, but that doesn't impress people like "Ultra Super High Modulus Carbon Fiber".

The big names may be using a more expensive prepreg, but the effect on the frame or on what the rider feels will be negligible IMO.  The designs may be better, but that's a separate argument and can be very subjective.  If they have 68% fiber versus 60% fiber, that could save about 100 g on a 1 kg frame, assuming the design uses the same amount of fiber (for equal strength and stiffness) and that they are able to use the higher fiber % composite for the entire frame.  The actual savings is probably less.  Most of the stuff they put out about carbon fiber is marketing speak.

I work for a company that makes a high performance thermoplastic resin.  Most of our material goes into molded and extruded parts, but we also make composite tapes.  I'm not a composites expert, but I think I am smarter than your average bear on composites and materials in general.  To me, the best measure of quality control is how well the fibers are wetted out.  If the fracture has a lot of 'dry' fibers sticking out or obvious delamination between the layers, that means it was poorly made and failed at a lower stress or strain than it should have.  It's tough to tell from the pictures, but it looks like the material was pretty well made.  If you smashed the seat stays of a name brand frame with a rock I bet you'd see the same thing.

Carbonazza, any chance for some close ups of the fracture surfaces?  Also, where did the rock hit the frame?  At one of the fractures, or in between?


edit- also, if anything is highly innovative in the carbon fiber, it's done by the fiber maker or prepreg maker and is available to all bike makers willing to pay for it. 

 

+1 for the 056/057 with carbon rims!  Got mine from Peter, and still loving it.  I don't think you can go wrong with either, but I went with the 057 because at the time (~May 2014), it would have taken an extra couple of months to get a 256, effectively making me miss most of the summer.

Nice!  I'm thinking of doing the same for my son.  Plus my wife says she wants a bike she can ride on trails.  I may have to build three more Chiners before I get another one...(third would be for my daughter)

Looking forward to the pics!  How do you like that saddle?  I still haven't found one I really like.  Tried one of the web saddles, but it broke on the first ride (I'm ~90 kg).