MTB dropper seatposts

How to choose an MTB dropper seatpost

It makes the biggest difference to descending, and it is the one piece of kit you miss immediately when you go back to riding without it. Three measurements determine the right choice, and the second causes the most ordering mistakes.

The diameter

• 30.9 and 31.6 mm are the most common, 34.9 mm is found on some recent frames, 27.2 mm is for narrow frames and gravel bikes.
• You can find the diameter on the original seatpost or in the frame documentation.
• A shim lets you fit a narrower post in a wider seat tube. The reverse is not possible.

Travel and overall length: the real pitfall

• Common travel ranges from 100 to 240 mm.
• It is not the travel that limits your choice, but the available insertion depth inside your seat tube.
• Measure the unobstructed depth before the bend in the down tube or the hose routing.
• A reliable method: measure from the top of the seatpost clamp to the centre of the saddle rails, then compare that distance with the measurements overall length and minimum insertion in the product specifications.
• A post that is too long will not drop low enough; one that is too short will not rise to your pedalling height.

Internal routing, external routing or wireless

• Internal : the cable or hose runs inside the frame. Neat and protected, but the frame must have an opening for it.
• External : fits any frame, including older ones, though the cable remains visible along the seat tube.
• Wireless (RockShox Reverb AXS): no cable, no housing, just a battery to recharge.

Mechanical or hydraulic

Cable-operated mechanical posts dominate the market: they are simple, repairable and unaffected by the cold. Hydraulic posts rise more smoothly and lock more firmly at any height, but need occasional bleeding. For everyday riding, a good mechanical post is the most sensible choice.

Supplied with or without a remote

Some models include a handlebar remote, while others do not — check before ordering. If one is included, make sure there is room for it on a handlebar already occupied by the brake levers, shifter and possibly a suspension lockout.

To find out more: How to choose a dropper seatpost

See also: Dropper seatpost remotes · MTB seatpost clamps · MTB saddles