None of their teardrop shaped mounts are big enough to fit the Cervelo S-series seat post. I don't mind the serrated teeth, they haven't slipped on my in probably 20k miles. I can't seem to find your Synapse mount. This is how I had the Dinotte mounted on my S2 but the race number mount eventually broke from fatigue (luckily I heard the light fall and recovered it mostly unscathed.)