Originally Posted by
Sam N
Does this replace the existing collar or go on in addition to it?
Giant's site says the seatpost is 30.9mm, but that product seems to only be available in 29.8mm, 31.8mm, and 34.9mm.
It replaces the existing collar. Seatpost collars are spec'd by the outside diameter of the seat tube that they clamp around, not the seatpost size. Remove your current collar and measure the diameter of the seat tube. To convert from inches to millimeter, multiply the number by 25.4.