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the Complete Guide to Dropper Posts
Dropper seatposts, or dropper posts as they are generally called, were barely around 10 years ago.
Nowdays they’re not merely a desirable accessory but a vital component for serious mountain biking.
Dropper posts also allow modified frame design—a steeper seat tube angle is possible since the saddle can be “dropped” out of the way when necessary but also be right there for support when necessary.
The only legitimate argument against having one is the weight penalty, if you could call it that.
Most mountain bike, gravel bike and cyclocross enthusiasts will tell you, though, a dropper post’s benefits far outweigh the disadvantages.
If you have not tried one out.
After the experience, you’ll not look back.
Dropper Post History
The idea has been around from the early days of mountain biking. The Breeze and Angel Hite Rite was the first attempt to make seat height adjustment on the trail easier.
Nothing worse than coming to a steep decent, then having to Stop.
Get off your bike.
Adjust the saddle down.
Descend. Ascent ahead. Stop … again. Adjust … again . . . phew , tires you out just thinking about it .
What a hassle!
Ok, this gizmo, the Hite Rite, is not a dropper post as such.
The function’s the same though, allowing quicker and more nimble saddle height adjustment.
The key was the spring clamped to the seatpost and anchored at the top of the seat tube binder-bolt mount.
A cable lever opened the binder-bolt via a quick release cable. Take your weight off, seat and post rises.
Plant your butt firmly down to lower saddle height. Lock the position.
That spring though: not the most elegant solution and you’re likely to damage it—and yourself—when you stack. The Hite Rite slowly faded away.
The modern dropper post comes into view with Wayne Sicz and his CNC machine c.2002.
Originally inspired by the Hite Rite, he put his new idea to Rock Shox. They wanted nothing less than suspension revolution and said “Nahhh…pass”.
Learn more about this unique, early stage in dropper post evolution, in Mountain Bike Actions’s article on the subject.
Whilst not exactly a suspension “revolution” in Sicz’s view, you could still make the case that it was.
Suspension keeps your wheels in contact with the ground in critical situations. Your dropper post enables you to stay close to your bike in those same circumstances.
How Does a Dropper Post Work?
Think of an office chair, computer chair, a chair with a simple piston and lever at any rate.
Lift the lever, push down a bit, down goes the chair. Or push the lever, make as if to rise out of the chair, up comes the chair as you rise.
Dropper post mechanics relies on pressurized gas or air. You change position, or lock down an existing position, through changing or stabilizing the pressure.
Practically speaking, a flick of the remote handlebar-mounted lever gives you the position you want.
This capability opens up your riding performance possibilities no end.
Using a dropper post, you’ll find you can rapidly adapt to rapidly changing terrain. The faster you can adapt, the faster you can traverse that terrain.
Imagine blasting down the descent. Then, in a jiffy, you’re attacking the next ascent having effectively altered your bikes geometry on the fly!
Spending more time in both a comfortable and efficient pedaling position over the duration of a ride means a massive advance in performance possibilities.
Mechanical, Hydraulic or Electronic?
In other words, from the most simple to the more complex. Differences hinge on how the remote lever exerts control on the dropper post unit.
Mechanical models are cheaper, easier to setup and easier to maintain.
Simply keeping things clean is a great habit to get into with each variation by the way. You get to to know the equipment as well—staying close and intimate reduces expense and maximzes safety.
If you’ve ever had experience with hydraulic disk brakes, then you’ll know what you’ll be in for with hydraulic dropper posts, aside from the extra expense at purchase.
The lever acts as a piston pushing fluid through the hose thus activating the dropper mechanism.
A clear advantage is the absence of a cable to wear out. The hose can also be shaped to most any angle, providing improved installation options.
The downside is that you’ll be replacing the fluid at the end of every season.
Electronic systems are neatly self-contained and function smoothly. But you’ll pay a premium for that.
Dropper Post Lever
You’ll either have a remote lever (most common) on the handlebars or the seatpost (most common in the early days).
They are most commonly thumb-operated in the same way as a gear shift lever.
If you get hold of a dropper post without a remote lever, there are plenty of aftermarket options available.
Running a single chainring? 1x gearing allows an ergonomic below-handlebar location for your dropper remote.
The Dropper Post Riding Experience
Getting through technical obstacles and especially downhill sections is where you’ll come to worship this addition to your bike.
Fully extend the seat for climbing. The saddle is right there for support at the touch of a lever.
Fully retract for downhill. A low center of gravity and being able to position your weight right back means a much more efficient—and safer!—descent.
The ability to get your saddle out of the way or have it available for support at the touch of a lever has become central to the MTB experience these days.
How Do I Choose the Right Dropper Post for My Bike?
Start with your bike’s seat tube. What is the ID or Internal Diameter?
You’ll find its either 30.9mm or 31.6mm.
27.2mm and 34.9mm ID seat tubes are also around though.
With gravel bikes catching on in a big way, expect to see more 27.2mm dropper post offerings.
One issue is stiffness. 30.9/31.6mm flex much less. But if gravel or cyclocross is your thing, flex is a minor issue.
Another issue is lack of accommodation for internal cable routing. Again not necessarily a big deal since your particular biking discipline is the key consideration.
All you have to do now is select a dropper post with the corresponding OD or Outer Diameter to your seat tube’s ID.
Next for consideration is the dropper post’s
-fit to your bike frame geometry
–fit to your physique
Measure how far down you can insert your existing seat post into your seat tube without obstruction.
Does it insert almost to the “hilt”? Or does a bend in the seat tube prevent it going all the way down?
For many mountain bikes, the seat tube curves at and/or is obstructed by the suspension mounting bracket.
Measure the maximum insertion length. Record it.
In common with seat posts, dropper posts have a manufacturer-recommended minimum insertion length.
This ensures the post’s stability in the frame, vitally important considering the forces applied in full flight on the trail or downhill.
You want neither a broken post nor ruptured seat tube precipitating a major crash event, shall we say.
How Much Travel Do I Need in a Dropper Post?
Most dropper posts have infinite adjustment—the post can be stopped and locked in at any point along the travel.
Some posts are available in fixed detents from a simple up and down to as many as 10 selections.
The benefit is in the improved riding experience that can come once you get used to which particular settings work in which riding situations.
The length of travel is the distance between when it’s fully lowered and fully extended.
Here’s a commonly applied rule for choosing a dropper post in terms of travel.
1 Move your seatpost to the highest position possible—your climbing setting.
2 Measure the distance from the top of seatpost collar to the seat rail (stack height) then subtract 50mm
(Your seat’s rails are what the seatpost clamp fastens onto to hold your seat firmly in position.)
Your measurement here is the maximum travel length for the dropper post that you can comfortably install.
Dropper posts are commonly available in 80mm, 100mm, 125mm, and 150mm versions.
Be aware that a dropper post’s overall length increases as the length of travel increases.
You want to avoid a post that’s too long, a mistake more often made than buying one that’s too short.
If you are a taller rider, you’ll probably be looking at a 150mm.
A shorter rider’s bike will have a smaller frame. Together with the height limitation, 125mm is the maximum post for consideration.
Say your stack height is 170mm. Subtract 50 from 170 =150. Therefore the maximum travel is 150mm allowing you to consider the whole range of dropper post lengths.
At maximum extension, you should be at your perfect climbing height.
Dropper Post Installation and Setup
Get your local bike shop to do it, unless you are really into DIY.
Placing a seatpost into a seatube is easy enough. However your dropper post needs to be properly connected to the remote lever via a cable in most cases.
The main consideration is whether you have internal or external cable routing.
Internal, or stealth cable routing, is most common, following the trend to internally rout all cables on mid- to high-end bikes, mountain bike or road.
The cable connects to the remote lever at the shaft of the post.
Internal cable routing is the best way to go. It’s a much nicer look. Or rather the absence of cables is the nicer look.
The cable is also protected from damage, dirt and debris. The action becomes stiffer over time as dirt enters and accumulates.
If you’re installing a dropper post to an older mountain bike, external cable routing allows you to get up and running quickly. A few zip ties and you’re good to go. Following a rear brake hose works well.
And should the cable sustain damage, repair is easy. Ongoing maintenance is also easy.
For internal cable routing getting the cable routed internally is the tricky bit.
You could use a magnetic pickup tool. Learning how to manipulate it and get the cable threaded and linked up would involve a bit of trial and error.
Threading a string, sucking it out with a vacuum, then drawing the cable through is another suggestion.
Many bike assemblers thread lengths of 2mm tubing through bike frame tubes to carry brake and derailleur cables to their destinations.
This type of tubing is stiff so it can be straightened or shaped into the right curve.
There is a learning process with these methods. Again, better to have your local bike technician install the post for accurate and smooth operation out on the trail.
Is it OK to Drill a Hole in the Lower Seat Tube?
No. Never do this!
The potential for a hole to interfere with your bike frame’s integrity is too high. For safety’s sake there are other ways.
You need a frame that has been designed for internal cable routing, particularly for dropper posts.
Dropper Post Maintenance
Your dropper post is subject to an intense workout across the mountain biking season.
The constant forces applied to the lever-cable/hose-post system means you need to be vigilant to ensure your post keeps working exactly as it’s designed to.
The main unit uses gas or hydraulic fluid, or a combination. Having a skilled professional service it is best.
Watch for the following:
- sagging under your weight (not being able to support you as when it was new)
- leaking seals
- more play than normal
- slow, lagging extension
- unusual noises (the sounds of un-silence)
A normal service involves (among other things and where necessary)
- replacing seals
- bleeding off and replenishing hydraulic fluids
- pressurization of gas or fluids
Avoid incorrect cable tension or poor hydraulic bleed. This can lead to poor travel extension and thus overtightening the seatpost binder bolt.
Also avoid grabbing and lifting your bike by the saddle with the dropper at the lowest position. You may find air will get sucked into the unit that will probably necessitate professional attention.