Bicycle Seatposts, Clamps, Bolts & Shims — Getting the Right Fit

The seatpost is one of the most overlooked components on a bike, yet it plays a crucial role in comfort, fit, and riding position. Getting the right seatpost — and the right clamp to hold it — is straightforward once you know what to look for.

Seatpost Diameter — Measure First

Seatpost diameter must match your frame's seat tube inner diameter exactly. Common sizes include 27.2mm (road bikes), 30.9mm and 31.6mm (mountain bikes), and 34.9mm (some older frames). Even a 0.2mm mismatch will cause slipping or damage. If your frame is between sizes, a shim can bridge the gap.

Seatpost Length and Setback

Length matters — you need enough post inserted into the frame (at least the minimum insertion mark) while still achieving your correct saddle height. Setback refers to how far the saddle rail clamp is offset behind the post centreline. Inline posts have zero setback; offset posts move the saddle further back for a more stretched riding position.

Materials

• Aluminium — affordable, durable, and widely available
• Carbon fibre — lighter and better at absorbing road vibration, but requires careful torquing to avoid crushing
• Titanium — excellent vibration damping and corrosion resistance, premium price

Dropper Seatposts

Dropper posts allow you to lower and raise your saddle on the fly via a handlebar-mounted lever — invaluable for mountain biking. Key specs are travel (how far the post drops, typically 100–200mm), actuation type (cable or hydraulic), and compatibility with your frame's internal or external routing.

Seatpost Clamps and Shims

The seatpost clamp wraps around the top of the seat tube and clamps the post in place. Clamp diameter must match your frame's seat tube outer diameter. If your seatpost is smaller than the frame's seat tube, a shim fills the gap — useful when fitting a 27.2mm post into a 31.6mm frame.

Browse our seatposts, clamps, bolts and shims for a full range of sizing options.