Common Specifications and Parameters of Bicycle Seatposts

Outer Diameter Size (Unit: mm)
27.2: Main size for road and gravel bikes, used on some mountain bikes.

30.9 / 31.6: Commonly used on mountain bikes, balancing stiffness and weight.

34.9: Popular size for modern mountain bikes (especially dropper posts), providing higher strength.

Travel Length (Dropper Post Only): 60mm to 200mm+, commonly 100mm, 125mm, 150mm, etc.

Total Length: Usually 300–400mm, should be chosen based on the frame seat tube length and saddle height requirements.