Duragrouch

Carbon fiber can be real tough under just fatigue loading. I would still think that having the layup be thicker at the spoke holes would be most efficient, and that they could add strips or patches in those areas during layup, but maybe just better to make the whole rim thicker at the root.

I personally would not go carbon rims unless for disc brakes, and ultimate failure loading stronger than aluminum (quite possible), but also looking at the failure mode in a severe crash versus aluminum; One LBS recommends against carbon anything unless a bonafide racer, due to fragility, difficulty to repair, easier to damage from bad installation, and failure mode of sharp edges. But in fatigue life, it tends to be much superior to aluminum; Boeing didn't go more expensive with composites on the 787 airframe for nothing, it's a more efficient, and should be, more durable design, especially in fatigue cycles.

The other thing I don't like about any composites is inability to recycle, instead of going into the landfill. I think the carbon itself could be recycled, the hard part is the resin holding it all together, both separating and recycling that. If the world starts making massive numbers of wind turbines (as I think they should), if the blades are composite, this is a big issue in the long term; I don't know if they are composite or aluminum or steel.

terrymorse 

Carbon fiber composite is easier to repair than steel, and much easier to repair than aluminum.

Duragrouch

As someone who has repaired fiberglass layups with a bare minimum of materials, I would kinda agree. However, some bikes shops will treat a bike with a damaged carbon frame as persona non grata (to work on *anything*) unless repaired by recognized experts in carbon repair, and based on other threads, I think there are only a small handful. Calfee is one.

Steel, on the other hand, can find competent repair in most cities, and was the gold standard for overseas expeditions, as there are competent steel welders and brazers even in the third world.

Aluminum welding is becoming increasingly common, and the bike industry has mostly shifted from 6061-T6 which required post-weld heat-treating, to 7005 which does not. However with really thin-wall aluminum tubes on race bikes (I can elastically dent them by pushing on the top tube with my thumb), welding may be tricky.

A minor dent in a steel or aluminum frame tube is usually non-critical. Some bends can be straightened. Serious ultimate failures are usually of a non-catastrophic failure mode. Carbon fiber doesn't dent or deform plasticly, and is usually minimum thickness on bike frames, so the same impact often results in a soft spot or cracking. Might not be critical, but will be considered as such by many bike shops. Serious failures are often catastrophic, completely coming apart. I wish that were not true, because I would like to lighten my bike with it, it's becoming affordable.

EDIT: Sorry I got into the weeds on frame materials, when this is about wheels. But I think a repair to a carbon wheel may be even more tricky and critical, than a carbon fiber frame. Then again, serious damage, even a small fatigue crack on an aluminum rim means the rim is a dead parrot. So perhaps a carbon rim will be more durable.