Stiff carbon rims don't necessarily transmit _more_ force to the spokes (the total force is dictated by the impact, not the material), but they may focus the force on much fewer spokes. With a high hoop strength and minimal deflection away from round, the force is going to be concentrated on the few spokes directly opposite the the impact. Meanwhile, a rim that allows more deflection away from round spreads the force through many spokes, as more spokes not directly across from the impact point see their tension rise in order to maintain the roundness.
However, using thinner spokes that can stretch elastically can also help spread the force to more spokes, as the spokes directly across from the impact will give a little and raise tension in the surround spokes even if the rim maintains perfect roundness.
The plain old longevity of wheels could definitely be a factor, but I think that also points to smart hub flange designs being important. If the flange angles, hole shape, and hole tolerances are well designed, the forces at the bend will be spread through more of the spoke head and bend, limiting stress risers and increasing the fatigue life.
Oct. 5, 2022, 1:05 p.m. - Justin White
Stiff carbon rims don't necessarily transmit _more_ force to the spokes (the total force is dictated by the impact, not the material), but they may focus the force on much fewer spokes. With a high hoop strength and minimal deflection away from round, the force is going to be concentrated on the few spokes directly opposite the the impact. Meanwhile, a rim that allows more deflection away from round spreads the force through many spokes, as more spokes not directly across from the impact point see their tension rise in order to maintain the roundness. However, using thinner spokes that can stretch elastically can also help spread the force to more spokes, as the spokes directly across from the impact will give a little and raise tension in the surround spokes even if the rim maintains perfect roundness. The plain old longevity of wheels could definitely be a factor, but I think that also points to smart hub flange designs being important. If the flange angles, hole shape, and hole tolerances are well designed, the forces at the bend will be spread through more of the spoke head and bend, limiting stress risers and increasing the fatigue life.