Can someone tell me the difference between the Cannondale CAAD 8 and Synapse if both have the same components?

CAAD8 is stiffer (and used to be racier with a shorter head tube than they use now), and Synapse dampens vibrations better.

That's basically it.

Thx BarracksSi. The head tube is 0.5 cm shorter on the current Caad8 compared to Synapse. There seem to be more people here talking about CAAD. More racers here?

I think more people talk about CAAD because it's a catchy trademark and Cannondale's aluminum race frames have proven to be really good bang-for-the-buck. In the past, the CAAD series were indeed pro-level race bikes. You just won't easily find a better aluminum frame in terms of efficiency and handling.

The Synapse, IMO, is still plenty of bike for almost everyone reading Bikeforums. Picture it alongside other manufacturers' Roubaix-type bikes, intended for making rougher pavement less annoying (Cannondale's sponsored teams use, or used, it for the Paris-Roubaix race, for example). It's not gonna have rocketship-like acceleration, but it'll be a little nicer on longer distances.

I had a previous-generation CAAD8 and chose it over an alloy Synapse because I wanted a faster, harder-riding road bike so I could pretend I was good. Looking back now, I think I would've been just as happy with the Synapse.

I would get a Caad 10

If you're just starting the sport, go with the synapse. It's the fast sports coupe, while the CAAD is sports car. If you're going to ride a freshly paved track, get a CAAD. If you ride frequently for enjoyment on a real road, get the Synapse.