Does anyone remember those dark days of riding in a pre-dropper world? Being forced to choose between stopping to lower your saddle or dealing with a high post limiting the fun factor on the descents? Sad times, to be sure. But in all seriousness, dropper posts are one of the most revolutionary products to come along in mountain biking in the past few years. Many talking heads in the mountain bike world–myself included–would rank the dropper post as the single best upgrade you can make to your mountain bike.
But first, a bit of history. Way back in the early 1980s, Joe Breeze–one of our sport’s godfathers–developed what is arguably the precursor to the modern dropper post: the Hite-Rite Seat Locating Spring. Catchy name, I know. Basically, it was a spring that attached to the seat post collar on one end and to the post itself at the other. To operate it, one would reach down, flip open the quick release, weight the saddle to lower it, and close the quick release. The saddle was now out of your way and you were free to shred. When it was time to go back up, flip open the quick release and the spring would push the post back up to the proper height.
Next came the Gravity Dropper, in the early 2000s. With their distinctive rubber dust boot, they were hard to miss. The mechanical post has a fairly simple design with the “Classic” model only having two positions–all the way up or all the way down. Gravity Droppers are still available, and actually have a bit of a cult following because of their reputation for ease of maintenance.
The Maverick Speedball, while short-lived, refined the dropper further. Instead of the fixed positions of the Gravity Dropper, the Speedball was infinitely adjustable due to its hydraulic internals. Keen observers will notice that the Speedball looks remarkably similar to Crankbrothers Joplin, and for good reason. When Maverick dissolved, they sold the Speedball design to CB, which rebranded it as the Joplin.
As we wrapped up the first decade of the 2000s, dropper posts were becoming a common sight and were even being spec’d as original equipment on certain trail bikes. With their popularity booming, more and more manufacturers got into the fray including KS (Kind Shock), RockShox, and Fox.
That more or less brings us to today, where the majority of trail bikes–midrange and above–are coming spec’d with a dropper post from the manufacturer. However, since many of us have older bikes–and droppers are such a great upgrade–we’ve put together this buyer’s guide to help you with your decision-making process.
There are a couple of choices to make in regards to sizing. First off is choosing the correct diameter for your frame. While there are numerous possibilities for seat post diameters, thankfully the industry has settled on just a few. Far and away, the two most common are going to be the 30.9mm and 31.6mm sizes. Other less commonly available sizes are 27.2mm and 34.9mm. Many hard tails–old and new–use the smaller 27.2mm size, so it’s good to see several manufacturers now offering posts to fit those frames.
I should note that most companies recommend against–or outright forbid–using a shim on a dropper post. With a shim, you may have to tighten your seat post collar beyond the dropper’s torque spec, causing poor performance or possibly even damage to the internals. I, for one, think shims are a bad idea anywhere on a bike.
The other size considerations you have to make are somewhat interrelated. One is the travel of the post, and the other is the overall length of the post. Typically, droppers are available in one of three travel increments: 100mm, 125mm, and 150mm. As the length of travel increases, the overall length of the post has to grow as well. This is why you need to be very careful when selecting a dropper. For instance, most small frames will not be able to accommodate a 150mm travel dropper. Unless you happen to have ridiculously long legs for your height, the post will be too high when it’s fully extended. On the other hand, tall riders will need to pay more attention to the overall length of the post. Just like a standard post, droppers will have a minimum insertion line. If your post is sticking too far out, it’s possible to crack the frame’s seat tube. It’s no joke: I’ve seen it happen firsthand.
In order to offer the most drop possible for a given frame size, bike companies are designing frames with shorter and shorter seat tubes. Even so, there will be travel limitations for certain bikes. If this all sounds confusing, consult your local bike shop.
After determining what size post you need, you have to chose the proper cable/hose routing for your needs. Thankfully, this is quite simple since there are only two options: external, or internal (often referred to as “Stealth” routing). Functionally, droppers should operate identically no matter what their routing.
External routing runs the cable/hose from the remote on your handlebar to the post on the outside of your frame. Typically, it runs either on the side of, or underneath, the frame’s top tube. External routing makes it easy to mount the post–a good thing if you’re using your dropper on multiple bikes. Most–but not all–external posts have their release mechanism at the post’s head. When the saddle is dropped, the excess cable/hose can rub your rear tire when your suspension is compressed, or rub your calf, which is annoying. Aesthetically, external routing doesn’t look as clean as internal.
Internal routing has the cable/hose run–wait for it–on the inside of the frame. Most new bikes have a provision for an internally-routed dropper. Although, for maximum compatibility, it’s not uncommon to see a frame that can run both types of droppers. Depending on the design of the bike, the cable/hose may enter at the head tube and disappear into the frame. On other bikes–like my Kona Process–it first runs externally along the down tube before entering the frame through a hole in the seat tube. Internally-routed posts look cleaner and get rid of that extra loop of housing. The major drawbacks with internally-routed posts are the higher cost, the need for a compatible frame, and increased installation difficulty–you won’t be able to switch an internally-routed post to another bike easily..
Hydraulic, Mechanical, or Electronic?
Most posts use some sort of hydraulic mechanism to make the post go up and down. How that mechanism gets actuated can be done in one of three ways. The most common method is mechanically. A braided steel cable, like you’d find inside your shifter, runs from the remote to the post. The second option is a fully hydraulic post. Instead of a cable and housing, hydraulic fluid runs through a hose from the remote to the post–very similar to your bike’s brakes. The last option, electronic, is the newcomer on the scene. So far, Magura is the only company to offer an electronically-actuated post. Their system is entirely wireless, using an ANT+ signal to tell the post to get out of the way.
Generally speaking, cable systems are easier to set up initially than hydraulic, since you don’t have to bleed the line. For longevity, hydraulically-actuated droppers can have longer service intervals since it’s a closed system. Cables can get contaminated by dirt and moisture, degrading performance.
The vast majority of posts are going to offer infinite adjustment. That means you can stop the post at any point along its travel. Many riders prefer this type of post because of the ability to fine tune their saddle height depending on the situation. A few posts come with preset positions. Fox chose to go with three for their now-defunct DOSS post, and Specialized has posts with either three or ten preset positions.
Alright, now that we’ve covered the evolution of the dropper and how to choose one, let’s go over some specific models that are available today: click to page two for specific options.