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Bike component fitment: bottom bracket, headset, seatpost, axle

30.6 mm seatpost (30.6 mm) vs 31.6 mm seatpost (31.6 mm): specs compared

Updated 05 September 2026.

3
specs differ

30.6 mm seatpost (30.6 mm) and 31.6 mm seatpost (31.6 mm) differ on 3 specs: diameter, designation, typical frames.

Spec30.6 mm seatpost (30.6 mm)31.6 mm seatpost (31.6 mm)
Diameter30.6 mm31.6 mm
Designation30.6 mm31.6 mm
Typical framessome older oversized aluminium road and MTB framesmany mountain bikes and gravel frames, older oversized road frames, and the other common dropper-post diameter

Questions and answers

How do 30.6 mm seatpost (30.6 mm) and 31.6 mm seatpost (31.6 mm) compare?

30.6 mm seatpost (30.6 mm) and 31.6 mm seatpost (31.6 mm) differ on 3 specs: diameter, designation, typical frames.

Compared here

30.6 mm seatpost (30.6 mm)31.6 mm seatpost (31.6 mm)