MTB seatposts

How to choose an MTB seatpost

A rigid seatpost still makes perfect sense for cross-country riding, a second bike, or simply when you want low weight and no maintenance. Dropper seatposts are covered on a separate page.

Diameter and length

• 27.2 / 30.9 / 31.6 mm cover the vast majority of mountain bikes; 34.9 mm is found on some frames.
• The diameter is engraved on the original seatpost or given in the frame documentation.
• Lengths range from 350 to 400 mm : choose a post long enough for the minimum insertion mark remains inside the frame and is never visible.
• A shim lets you fit a narrower post in a wider seat tube. The reverse is not possible.

Straight or with setback

• Straight (0 mm setback): the saddle sits over the post’s centreline. A forward position suited to cross-country riding and modern frames with steeper seat tube angles.
• With setback (15 to 25 mm): moves the saddle back, lengthens your riding position and eases pressure on your knees on frames with a very slack seat tube angle.
• You can compensate for some setback by adjusting the saddle along its rails, but only by a few millimetres. Beyond that, you need a different post.

Aluminium or carbon

• Aluminium : robust, affordable and unfazed by a slightly overtightened clamp. The default choice.
• Carbon : genuinely absorbs vibrations and saves 80 to 150 g. In return, it requires assembly paste and tightening to the specified torque, and will not tolerate an overtightened clamp.

The saddle clamp

It holds the rails and sets the saddle angle. A two-bolt saddle clamp allows much finer adjustment than a single-bolt one, and you can feel the difference in comfort. Also check that it accepts your saddle’s rail type: oval carbon rails do not fit every clamp.

Proprietary standards

Some posts use a specific mounting system — SDG I-Beam, for example — that only accepts saddles from the same brand. It is a sensible, lightweight choice, but commits you to a particular saddle as well as a post.

To find out more: How to choose an MTB seatpost

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