The new and highly anticipated XLab Sonic Wing is here!! Cervlo Specific Alloy Rear Hydration Carrier. You know those mysterious two holes in a Cervlo seatpost? Well, this Carrier will fit in there, a nice tight fit. Is compatible with the Cervlo P2Cs, P3Cs and P4Cs. Consider also the Carbon Sonic for XLAB's carbon version. Don't buy other Cervlo specific rear hydration carriers. Why? For all the reasons you will read about below. Plus, don't forget our business is the Hydration and Storage business and nothing else. Trust the professionals that are dedicated to your Hydration and Storage needs. Our carriers are Wind Tunnel Proven and owned by World Champions. They are proven to be the most aerodynamic and versatile in the market today...period. Can be inverted for a lower position on the saddle, or keep it upright for a low drag higher position. Has 30 different positions available, so that you can have a custom fit position that is both comfortable and aerodynamic. 3 different carrier angles and 5 different bottle angles for each position. Because the carrier fits on the seat post we have not discovered any seats that you cannot use including the long Fizik, SMP, Selle Italia, Selle San Marco, Terry and others.