Originally Posted by
Triguy
I thnk of the Synapse and S1 as very different bikes. One is more of a comfort bike, one is more of an aero/race bike. Thats not the final word on their use, but it's probably a hint to look at the type of riding you'll be doing and what you want out of your bike.
It's worth noting though that the Synapse is probably one of the least plush of the comfort bikes geometry wise, but the carbon vs alum frame are probably going to ride quite a bit differently.
Definitely nix the the Carbon 3 if it's the wrong size, you'll regret it later.
If you're going to race I may lean towards the S1 for the slightly more aggressive position and (I'd assume) more responsive frame. If you're just looking for a great all around fast road bike the Synapse is excellent and what I just bought.
Both nice bikes.