The best dropper post has the longest stroke you can run on your particular frame: The low seat tube height of Transition's size large Sentinel allowed PB's Mike Kazimer to enjoy the benefits of a 170-millimeter RockShox Reverb. Not all of us will be that lucky.
Ask your local mountain bike dealer what length dropper seatposts are available and the answer will most likely be, “125, 150, or 170 millimeters.” With dropper posts, more is always better. If you crave steep, technical descending, you’ll probably want to get as low over the bike as possible. If you’ve purchased a trail bike with rider-forward geometry, you may have noticed that effective seat tube angles that are near or exceed 75 degrees require a longer-stroke post to achieve an optimum pedaling height, while still dropping low enough to be comfortably stowed for the downs. Trouble is, depending on your body or your bike, you may not have the option to choose a longer dropper.
What goes up, must come down. The lower section of dropper seatposts must be able to contain the telescoping length of the post, as well as the actuation and sealing bits. So, like the proverbial iceberg, there is always more dropper post lurking below the sliding bits than above – and most of that lower section has to be stowed inside the frame. Some frame designs have S-shaped seat tubes or suspension-pivot ingress that restricts how deep the post can be inserted or, if your frame has a tall seat tube, a long-travel post may still place the saddle above your pedaling height at full insertion with the seal-head slammed against the clamp. You may want that 150-millimeter dropper, but be forced to settle on the 125-millimeter option for reasons beyond your control.
It’s an equation that favors tall riders, for sure, but short people aren’t the only ones who are affected. Medium and large-sized frames are typically spec’ed with 150-millimeter posts (Some large and extra-large sizes come with 170-millimeter models), which often results in a situation where the rider is only five or ten millimeters above his or her comfortable saddle height with the seatpost slammed as low as it can go in the frame. The obvious solution is to downsize to the next smaller post. If it’s a new purchase, most bike dealers will do that for you. If it’s a used bike, it will cost you a lot of money – which begs the question: “Instead of being forced to downsize 20 to 50 millimeters to a shorter-stroke post, wouldn’t it be great if you could simply adjust the stroke of your existing post in small increments and get the maximum drop?”
User adjustable dropper posts seem like a good idea to me, but I don’t manufacture droppers, nor do I design the frames they are intended to fit, so I did some research and asked a handful of component makers who do to weigh in on the subject. To my knowledge, only three dropper post makers offer user-friendly adjustments in some form. 9poin8’s Fall Line dropper is internally adjustable with spacers. Eightpins and BMC have integrated posts (built inside the seat tube) that can be adjusted either for stroke or maximum extension. Integrated posts are included in this discussion because the concept could offer customers both adjustability and longer travel. Here's what I discovered:
9point8 Fall Line
About the Future: Jack Pittens, 9point8 Co-Founder
The 9point8’s Fall Line post
is designed to be internally adjustable by adding plastic top-out spacers, which are available in 4, 8, and 25-millimeter lengths. The process entails disassembling the seatpost, but the mechanical internals are simple to work on and there is no messy hydraulic fluid to deal with when you crack it open. They offer a detailed instruction video
to simplify the process, but if you don’t want to fuss with that, 9point8 offers its droppers with strokes from 75 up to 200 millimeters in 25-millimeter increments. An easy-to-read chart lists both the fixed and telescopic lengths of the Fall Line range, so you can order the longest possible stroke for your particular frame.
What are your thoughts about future dropper seatposts being built into the frame?
As with most changes, there will be pros and cons with a frame-integrated dropper post. We believe that there should be an interface standard across as many brand of droppers and frames as possible, and that they should be backward compatible, so that conventional droppers or fixed seat posts can also be used so the consumers have the choice to configure their bikes as they prefer. We generally feel that the benefits of integrating a dropper will be incremental and not revolutionary. For example, if the goal is to have a dropper with a stiffer stanchion tube, the larger diameter desired to achieve this could be accomplished by going to a larger seat tube size (say, 34.9mm) and does not require an integrated post to do this. If the ultimate goal is weight savings, then yes, there are incremental benefits to integrating the dropper.
Is there a need to standardize some basic seat tube diameters and minimum insertion lengths?
One thing everyone would benefit from is published maximum insertion depth for the dropper in the frame for each specific size! This would be so easy to do. It’s just another dimension on the frame geometry drawing. This would complement dropper manufacturers that similarly publish dimension and fit information on their droppers, and it would help the consumer more readily determine what length and stroke can fit their bike. Though not standardization, it would benefit the aftermarket consumer immensely.
In a perfect dream world, we’d love to see all bikes have nice straight uninterrupted seat tubes that extend to the bottom bracket, and do not have water bottle bosses or suspension pivots intruding into the interior, so that the length of dropper uses is not restricted. The reality is that nearly every bike brand has their take on the optimum frame and suspension design and many of these do not play nice with long droppers. Through natural selection, the market will determine how important it is to accommodate longer stroke posts.Fall Line Notes: Positives:
Conventional design fits all popular brands. Available in a large number of stroke options. Can be user-adjusted with a low-cost spacer kit. Mechanical operation simplifies disassembly process for garage mechanics.Negatives:
Conventional configuration requires up to 300 millimeters of precise insertion in the frame. Small-diameter stanchion is flexible.
Eightpins Integrated Dropper
The Eightpins dropper offers what may be the most promising solution for the future. The Eightpins dropper is integrated into the frame, so you can’t have one unless your frame is customized to accept the internal mounting, or you purchase a Liteville – they’re the only manufacturer who offers the option at this time.
The mechanically-actuated Eightpins post
is inverted, meaning that the larger-diameter section of the post is the sliding part that supports the saddle. The smaller-diameter section of the dropper is anchored inside the frame’s seat tube with a simple through-bolt and, up top, a seal-head replaces the traditional seat post clamp. One of the benefits of this arrangement is that only the first 100 millimeters of the seat tube (where the seal-head is inserted) requires a precise fit. As long as there is sufficient clearance for the Eightpins‘ internals, the rest of the seat tube can be shaped any way the designer wants it.
Eightpins addresses the adjustability issue with a 4-millimeter bolt located under the seatpost clamp which reduces the height of the post at full extension. The manufacturer installs the longest stroke post that will fit inside the frame, and once the customer has established his or her maximum saddle height, the upper section of the post is cut to the ideal length that will allow it to retract all the way down to the seal-head. The two adjustments ensure that the customer always gets the maximum stroke: the perfect pedaling height and the lowest possible dropped position. Eightpins offers frame makers four stroke-lengths, ranging from 150, to 225 millimeters, so there should be enough wiggle room between them to ensure that every customer can properly ditch the saddle when the moment arrives.
Interview with Eightpins' Andreas Haimberger
What advantages does the Eight Pins design offer in the realm of adjustability to both the rider and to the bike maker?
As you mentioned before, our system is capable to adjust height and travel separately. Riders benefit from the lowest possible saddle height in dropped position and maximum travel. And the bike maker can sell a bike which can be fully adjusted to the customer without any compromises like the choice of a shorter travel version instead to a longer one to provide more adjustability.
The maximum travel for the system is defined by the seat tube length, the position of the Postpin mounting point, and the needed insertion length of the seat tube in the frame (100 to140mm). This will be optimized for each frame. If a rider needs less seat tube pullout than the available maximum travel in the current frame, travel can be reduced with spacers. Without travel reduction, the seatpost head would bottom out onto the seal.
What modifications would bike makers need to do to switch to integrated dropper posts?
To provide the maximum travel and adjustability, a straight seat tube is needed. In case of Eightpins, the ID of the seat tube has to be 34.9 mm, and the Postpin mounting standard has to be provided. Our setback version gives the bike makers more opportunities to work around bent seat tubes to reach the goal of clearance for the rear wheel.
Would it be possible to standardize integrated post mounting so customers are not wedded to one single supplier or design?
Sure it would be possible. It´s just a question of the willingness of the dropper post manufacturer to agree on one standard.
Eliminating the start-up expense of tooling frames for integrated droppers, are the manufacturing/OEM costs the same for a conventional dropper post?
In the case of Eightpins versus a hydraulic dropper post they are not. Our system works mechanically and the parts are more complicated to machine.
A hydraulic dropper post has mostly round parts which makes production easier. We are working on efficient machining processes to reduce the costs and make the product available to a wider bike spec. We see a hydraulic gas spring as a compromise. This technology works best in an office chair with linear movement. A seatpost is a part which gets bent during riding and in most seatposts the hydraulic gas spring is part of the structure. This is not a good environment for an integrated hydraulic gas spring.
Is the integrated dropper the best solution for future mountain bikes?
After more than 120 years of squeezed seatposts, it´s time to replace the old technology of seat clamps. So many things changed on bikes. Now it´s time for something new in the area of seatposts. We don´t see a way to solve the adjustment and travel problems with the current seatpost design. From our point of view, an integration is the best way to overcome these problems and make mountain bikes better.Eightpin Notes: Positives:
Most promising new concept for future mountain bikes. Stanchion tube can be trimmed, and maximum stroke can be adjusted separately to maximize seatpost drop for every rider. Integrated design allows for a larger diameter, more rigid stanchion tube while reducing weight. Elimination of external seatpost clamp seals frame and reduces sliding friction.Negatives:
Post is dedicated to the frame (The seal-head can be removed from the Liteville and replaced by a standard seatpost and clamp). Frame design is restricted to straight seat tubes, which may not play well with some linkage configurations.
BMC Trailsync Integrated Dropper
BMC is newest to the adjustable dropper game, with a frame-integrated design that they debuted on their 2018 Speedfox.
Instead of adjusting the “Trailsync” dropper post’s stroke, BMC designed a slip-over saddle clamp that offers 25 millimeters of vertical adjustment. The upper part of the mechanically operated BMC dropper is a simple tube that can be cut shorter with a hacksaw if 25 millimeters of adjustment is not enough to achieve your correct ride height. Should you sell your BMC to a taller rider, the internals are bone-simple to access, and reportedly, full-length replacement tubes will be readily available. Presently, the BMC post is limited to 100 millimeters (insiders say that longer stroke versions will soon follow), and the Trailsync system will only appear on BMC products That said, the Trailsync post is worth a closer look in this context.
BMC’s Trailsync post is mechanically actuated by a spring-loaded pin that locks into preset holes in the telescoping tubes (Gravity Dropper comes to mind here). The simplicity and field-proven success of its mechanism ensures a measure of reliability, and because there is literally nothing but air inside the sliding tube below the saddle, it can be trimmed to suit the customer’s pedaling height without reducing the stroke of the dropper mechanism.
Unlike the Eightpins concept, which was intended from the start to cross-over to any number of frame
designs, the Trailsync's external, spring-loaded indexing pin apparatus might prove to be problematic for some frame configurations. That said, Trailsync appears to be a viable alternative to fixed-length droppers with a user-friendly adjustment system.
Trailsync Notes: Positives:
The simplicity of BMC's built-in dropper is apparent here. The gold device (left) is the pin that indexes in holes drilled in the dropper stanchion.
Promising, lightweight design alternative is linked to the shock's remote pedaling switch. Upper saddle height can be adjusted separately by trimming stanchion tube, or via the sliding seat clamp attachment without affecting the dropper's stroke. Super-simple pin-type dropper mechanism should last a lifetime. Integrated design seals seat tube and provides a large-diameter, more rigid stanchion tube. Negatives:
You can only get one if you buy a BMC, and if BMC abandons the concept and the post fails, your frame will be worth scrap prices.
Fox Racing Shox: Three Questions for Mark Jordan
How important is user-adjustable travel to Fox and your customers?
It is something we are aware of, but I don’t think it’s a problem for most riders.
Some bike makers are saying that, in the future, dropper seatposts will be built into the frame. What are your thoughts on this?
It’s a great idea and will probably happen one day. But it will most likely require the use of a specific brand/model seatpost because all of the most popular posts are very different.
Frames vary wildly as to how far the seat post can be inserted into the seat tube. Is there a need to standardize some basic seat tube diameters and minimum insertion lengths?
With most bike brands using 30.9mm or 31.6mm and offering as much insertion as their frame design can handle, it’s probably as standardized as it can be. One step further might be to settle on one seatpost diameter and look at what it will take to go to a bigger drop. But an XC bike has different requirements than an AM bike, so it may get complicated when considering what is lighter vs. biggest seatpost drop possible.
RockShox: Duncan Riffle talks Reverb
Is a user-adjustable Reverb on RockShox's radar screen?
Everything is on our radar. Are we working on that? I can't answer that question. It would be great if customers could micro-adjust their dropper travel, but I think we have that covered with all of the options that we offer now. We have a multitude of insertion lengths for our Reverbs that ideally, should cover most riders and frame designs. If a rider is caught between sizes, we should have enough insertion options so he or she will only be sacrificing ten or fifteen millimeters, not twenty or more.
What are your thoughts on supplying bike makers with an integrated dropper system?
As a brand, we are always looking into improving our technology. If that is something our customers are looking into, then we're looking into that as well. One thing we have learned over time, however, is that we won't bring in a new technology until it is proven by us and up to SRAM and RockShox standards.
With the popularity of convoluted seat tubes on the rise, maximum insertion depths are all over the map. How does RockShox deal with this?
We would be extremely happy if there were a set insertion depth for certain frame sizes, but that may never happen. You probably know as much as I do that part of the frame building design process is the art of it. Every designer has a different idea of how their creation should look. After you work out all the elements that keep it from breaking, the next step is making it not look like an alien contraption. You wouldn't want to restrict that because of some minimum insertion standard. Pinkbike's Take: