I have actually measured SP deflection on a number of bikes, and it can be quite significant, and there is pretty clearly a log relationship between SP length and deflection amount (visualize a seatpost curving evenly along it's length, and you can see why.) That said, generalizing that CF posts (more accurately, composite posts) deflect more or less than other materials is just silly - this flexibility is much more a function of design parameters than materials used.
Having said all that, where a composite does differ from ferrous seatpost materials is in it's damping characteristics. Vibrations propogate through materials at differing rates (wavelengths,) and combining dissimilar materials in a transmission medium can serve to disrupt (or dissipate) the energy transmitted in these waves (how/if this happens is again subject to design, and yes, you can use composites to increase the ability of a structure to efficiently transport energy.. ) The resonant properties of metallic frame/bike parts are generally immutable, but with composites a good designer can tailor these properties to their liking.
As a gross generalization, composite structures in bikes, which combine many different layers (and often materials) in their composition, AND are very dissimilar from the metal tubes of the bike, CAN be quite efficient at damping high frequency energy transmission - which results in less "road chatter" reaching the rider.
As an aside, by introducing carbon and other high stiffness/weight elements to a bike frame, one can also work to adjust the resonant frequency of the structure such that it is outside of the normal conditions encountered by the bike ("speed wobble" is quite often/mostly the effect of road vibrations equaling the resonant frequency of the bicycle, causing the entire unit to resonate/oscillate "sympathetically" at that frequency.)
MH
- building musical instruments since the early eighties...
Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
Coaching and bike fit - http://source-e.net/ Cyclocross blog - https://crosssports.net/ BJJ instruction - https://ballardbjj.com/
Having said all that, where a composite does differ from ferrous seatpost materials is in it's damping characteristics. Vibrations propogate through materials at differing rates (wavelengths,) and combining dissimilar materials in a transmission medium can serve to disrupt (or dissipate) the energy transmitted in these waves (how/if this happens is again subject to design, and yes, you can use composites to increase the ability of a structure to efficiently transport energy.. ) The resonant properties of metallic frame/bike parts are generally immutable, but with composites a good designer can tailor these properties to their liking.
As a gross generalization, composite structures in bikes, which combine many different layers (and often materials) in their composition, AND are very dissimilar from the metal tubes of the bike, CAN be quite efficient at damping high frequency energy transmission - which results in less "road chatter" reaching the rider.
As an aside, by introducing carbon and other high stiffness/weight elements to a bike frame, one can also work to adjust the resonant frequency of the structure such that it is outside of the normal conditions encountered by the bike ("speed wobble" is quite often/mostly the effect of road vibrations equaling the resonant frequency of the bicycle, causing the entire unit to resonate/oscillate "sympathetically" at that frequency.)
MH
- building musical instruments since the early eighties...
Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
Coaching and bike fit - http://source-e.net/ Cyclocross blog - https://crosssports.net/ BJJ instruction - https://ballardbjj.com/