I have the C5, almost identical to the C3. Rear clearance is about 33mm actual (measured), not the number on your tires. So it's all depending on the wheel rim width (internal). With the wider ENVE 4.5AR, the Schwalbe G-One 30mm expands to a tad more than 32mm and it barely clears. It's one of the biggest complaint I have about the C series form Cervelo. One option would be going to 650c wheels, and it would give you another couple of mm in clearance by the look of it.