Seatposts and clamps
The seatpost sets the saddle height and fore-aft position, the clamp holds it in the frame. Three measurements make the right choice: the seatpost diameter, its setback, and the outside diameter of the seat tube for the clamp.
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KS Southpaw MTB dropper post remote -
KS LEV Ci dropper post -
KS KG Drop 1.0 gravel dropper post remote -
RITCHEY WCS 1-Bolt Zero Offset aluminium seatpost -
RITCHEY Superlogic 1-Bolt FlexLogic carbon seatpost -
RITCHEY WCS 1-Bolt aluminium seatpost -
HOPE SEAT CLAMP QR quick-release seatpost clamp -
HOPE SEAT CLAMP BOLT bolt-on seatpost clamp
Three measurements before you change
It all starts with the bike. The seatpost diameter is set by the frame: it is usually engraved on the current post, and a calliper settles it between 30.9 and 31.6 mm, a 0.7 mm difference invisible to the eye, but a post that is too thin never clamps properly. The clamp, on the other hand, is chosen for the outside diameter of the seat tube, not the seatpost. Then there is length: the post keeps its minimum insertion in the frame, 100 mm at Ritchey, more if the frame manufacturer requires it. A workshop rule before removing it: a strip of tape around the post, flush with the clamp, to find your saddle height again to the millimetre.
Rigid or dropper post
On the road, a rigid post keeps the saddle exactly in place, and the choice comes down to setback and material. Ritchey seatposts come with 20 mm setback, 5 mm or zero offset, in aluminium or carbon, like the Superlogic FlexLogic that flexes to filter the road. On MTB and technical gravel, a dropper post lowers the saddle on the move to drop the centre of gravity on steep sections. The KS LEV Ci is operated from a flat bar or a drop bar, with the matching KS remote.
The clamp, the part people forget
Yet it does all the clamping, and too much costs more than too little: overtightened, it ovalises the body of a dropper post, which starts to stick. Hope seat clamps spread the force through a bolt with a spherical seat, bolt-on to fit once and for all, or quick-release to adjust the saddle without tools.
Frequently asked questions
How do I find my seatpost diameter?
It is usually engraved on the seatpost, near the minimum insertion mark, and listed in the frame's specifications. Otherwise, a calliper on the fitted seatpost settles it, because two common sizes such as 30.9 and 31.6 mm can't be told apart by eye.
Is the seatpost clamp the same diameter as the seatpost?
No. The clamp goes around the frame's seat tube, whose wall adds to the seatpost diameter. Measure the outside diameter of the tube, just below the fitted clamp.
How far can I raise a seatpost?
Up to the minimum insertion mark engraved on the seatpost, and never beyond the frame's own mark if it calls for deeper insertion. With Ritchey, 100 mm always stays in the frame: a 400 mm seatpost has at most 300 mm exposed.