30.9 mm seatpost (30.9 mm)
Which frames use a 30.9 mm seatpost, and how it differs from the sizes either side of it.
Published dimensions
| Diameter | 30.9 mm |
|---|---|
| Designation | 30.9 mm |
| Typical frames | many mountain bikes and full-suspension frames, and one of the two common dropper-post diameters |
Used on: many mountain bikes and full-suspension frames, and one of the two common dropper-post diameters.
30.9 mm is one of the two dominant dropper-post diameters (with 31.6 mm). A stouter seat tube resists the twisting loads a dropper puts on the frame. A 30.9 mm dropper needs a 30.9 mm tube; a 31.6 mm frame needs a shim to run it.
Frames and related seatpost sizes
Seatpost on a Giant Trance MTB30.9 mmSeatpost on a Giant Anthem MTB30.9 mmSeatpost on a Pivot Trail 42930.9 mm27.2 mm seatpost27.2 mm30.6 mm seatpost30.6 mmBSA bottom bracket shellthe frame's other threaded interface
SOURCES: BikeGremlin, Seatpost diameter sizes (standards) · BikeRadar, Bike seatposts explained: diameters, materials, lengths