I dont know for sure but I would say there is virtually no dampening effect and the carbon is for show only. The load is still supported by the alum core. A full carbon post may not absorb road buzz as much as you think.
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2010 Kestrel RT900SL, 800k carbon, chorus/record, speedplay, zonda
2000 litespeed Unicoi Ti, XTR,XT, Campy crank, time atac, carbon forks