Originally Posted by
thegnome
I have both. The CAAD is noticeably lighter (I'm no WW, so I haven't weighed them)... granted there is a groupset difference that likely accounts for a lot of this [SRAM Rival vs. Tiagra]. Frame weight differences are likely noticeable as well, but less-so as the frame of the synapse feels sturdier [thicker tubes, etc...] and likely weighs more as a result but you don't have the swings in weight between nicer components and less nice ones.
My Caad9 is about a pound lighter than my carbon Synapse. Both have rival groups. The Synapse came with heavy wheels and crank which I've upgraded so not sure about weights now (no scale) but the Caad still feels lighter.
Not sure what you mean about the Synapse frame feeling sturdier. I specifically bought the Caad9 over an alloy Synapse because the Synapse felt more flexy. Not as noticeable on the carbon model I eventually bought.