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.
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.
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.
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?