Originally Posted by
TrojanHorse
Go find a cannondale shop and test ride a synapse in carbon and AL and you'll have your answer.
Alternately, Specialized Secteur vs Roubaix.
Same geometry for both, shaped seat stays / chain stays for both, different frame material.
Fixed it for you. I have an aluminum Secteur and a carbon Roubaix. They ride similarly, but the carbon bike definitely soaks up more vibration.