I need to replace the seatpost collar on my 2005 Trek 5000 and can't figure out what size the replacement should be. Does it go by inlet diameter (27.7mm) or Outlet diameter?
The collar is sized by the outside diameter of the seat tube. Typically, there are three sizes available; 28.6 mm (1-1/8"), 31.8 mm (1-1/4") and 34.9 mm (1-3/8"). The 34.9 mm is sometimes listed as 35 mm.