The DELTA SONIC XL allows for a rear seat position and is 0.8" longer than the standard DELTA SONIC

Working closely with Cervélo and their wind tunnel testing results, XLAB developed an aerodynamic single rear system specific to Ritchey clamp seat posts with a 10 mm horizontal rear hole.

The DELTA SONIC XL fits snug into the seat post providing a sturdy non-sway bottle mount, for fast and safe access to your bottle. The DELTA SONIC XL rod can slide along the seat post for the best customized fit for you. XLAB recommends a 1" insertion minimum into the seatpost.