How to choose a dropper post

Distilling key considerations when choosing this critical component

Components How To

Longer travel dropper posts are preferred, but one needs to ensure saddle height is maintained.

Dropper posts are one of the greatest components for mountain biking, as a rider is able to get the best of both worlds of the high saddle pedaling position and a low descending position. But there are a lot of considerations when choosing the right dropper for you and your bike.

Basic Considerations

Make sure you buy the correct diameter post for your bike. Posts that are 30.9mm or 31.6mm are the most common, but 34.9mm and 27.2mm are also possible. In a pinch, seat tube spacers made by Problem Solvers work quite well.

Another key issue is internal or external cable routing. Older bikes generally use external while newer ones implement internal routing. Internal is better since there is no cable movement that can interfere with the rear suspension. Also, it gives a cleaner look and is never in the way. However, installation and maintenance are typically more involved.


Stack is always higher with longer drop posts. Some brands have higher stack than others.

To Get Maximum Drop

This is where it gets tricky, as the issue of stack and insert length are both critical in determining what dropper will fit in your bike for your height.

Stack is the measurement from the top of the seat post collar to the saddle rails. Then subtract about 50mm for the dropper post collar and the saddle clamp. This measurement is the maximum length of dropper you can run. Stack can vary from one bike to another given the same amount of drop.

Saddle Height

When the post is fully extended, the rider should be at the perfect pedaling saddle height.

Insert length is the length of post that will fit in your frame’s seat tube until it is obstructed. Find out how much seat post can be inserted into your frame. And then find out how much insert length a specific model dropper post requires.

Generally, RockShox and KS Lev require the shortest insert lengths, while Fox and Crankbrothers are on the higher end of the spectrum.

What dropper post do you run and what height drop?

About the author: Francis Cebedo

The founder of mtbr and roadbikereview, Francis Cebedo believes that every cyclist has a lot to teach and a lot to learn. "Our websites are communal hubs for sharing cycling experiences, trading adventure stories, and passing along product information and opinions." Francis' favorite bike is the last bike he rode, whether it's a dirt jumper, singlespeed, trail bike, lugged commuter or ultralight carbon road steed. Indeed, Francis loves cycling in all its forms and is happiest when infecting others with that same passion. Francis also believes that IPA will save America.

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  • uncyclist says:

    I need a 27.2 for a 29er hardtail and looks like only about a 100mm drop? I’m not too fussed about internal or external routing.

    • JRT says:

      The various Gravity dropper posts are not the newest or lightest, but those use coil springs and mechanical detent latches rather than the pneumatic air pressure which relies on seals that wear and are subject to contamination and damage. I think the Gravity’s coil spring based design is much more reliable and I would rather have that reliability. Opinions vary.

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