FOX D.O.S.S. Telescoping Seat Post
FOX hasn't hid the fact that they have been working on their first telescoping seat post, even going so far as to both show it at trade shows and put it under their sponsored riders at select events. But they have refrained from letting the media put any time on one - until now. The new post, christened D.O.S.S. for 'Drop On Steep Shit', features either four or five inches of travel (100mm or 125mm
) that is controlled mechanically, while a relatively low pressure air spring is employed to raise the post back up. Like many telescoping posts, the D.O.S.S. incorporates a 'Trail' position that sits 40mm down from full extension, often the ideal setting for rolling or technical terrain that still requires some pedal strokes to be thrown down. While that middle setting can come in handy, most who have used a post that offers such an option will admit that it can be tricky to find in the heat of the moment, which is why FOX have designed an interesting remote that employs two levers: pushing the larger lever will allow you to stroke through the post's entire travel (including stopping at the 40mm cruiser position
), while pushing the smaller lever will only allow the D.O.S.S. to either drop down 40mm or back up to full height. The three positions are referred to as 'Climb, Trail Descend', or CTD for short, that match up with their new three position CTD suspension that you'll get to read about in an upcoming article.
The 620 gram D.O.S.S post is actuated via a standard shift cable, with the housing anchor point at the post's head. Interestingly, the actuation arm is positioned at the side of the post instead of the more common location at the rear. This setup is not only less likely to be contaminated by spray thrown up from the rear tire, but also makes for smoother cable routing.
FOX D.O.S.S. details:
• FOX's first telescoping seat post
• Mechanical internals
• Air sprung (10 - 25psi to adjust return speed
• Three postions: full height, 40mm drop, fully dropped (climb, trail, descend
• 4'' or 5'' drop options (100mm or 125mm
• 30.9mm or 31.6mm sizes
• 620 grams
• Available in May, 2012
• MSRP $439 USD
| Our steed for the first day was Yeti's 150mm travel SB-66. The turquoise rig was fully kitted out with 2013 FOX suspension, of course.|
We spent two days riding both the new D.O.S.S. seat post and suspension offerings from FOX, with our first day in the saddle of Yeti's SB-66. The 150mm travel machine was fully decked out with 2013 goodies, including FOX's new Factory level, CTD equipped 34 Float fork and Float CTD Boost Valve rear shock. The CTD acronym stands for 'Climb, Trail, Descend
', which is the new three position damper that allows riders to choose from different levels of compression damping that best suit the terrain. There is plenty to cover on that front, but today we're going to introduce you to FOX's much anticipated D.O.S.S. telescoping seat post.
| The D.O.S.S.'s remote makes use of two levers, one to stroke through its entire travel and one that accesses the 40mm drop 'Trail' position.|
Dual Lever Remote
Pushing the large silver lever (above left
) allows you to stroke through the post's entire travel, including stopping at the 40mm drop postion that is ideal for fast, rolling terrain where you want a bit of extra clearance, but still need to pedal. Giving the inner black lever a push (above right
) will only allow the seat post to drop 40mm, a design that makes searching for the middle postion a thing of the past. Hitting it again will raise it back up to its maximum height. The dual levers are certainly more complicated than a single trigger, but it will be interesting to see if the added complication and size translate to more usability on the trail.
The design allows the same remote to be mounted on either side of the bar, top or bottom, without having to swap out clamps, and it is also features three different fore and aft positions. The remote lever isn't nearly as trim as what some of the competition offers, but its ability to be mounted every which way on the handlebar should allow most riders to find an ergonomic setup they can get along with.
| FOX built a testing jig that is designed to put the dual lever remote through hell by way of actuators that press the levers roughly every other second. Word from FOX is that they see the cable fail before either of the actual levers.|
| The post uses a one piece forged head and upper tube, as well as side mounted cable actuation.|
Side Mounted Cable actuation
FOX went ahead with the side mounted cable actuation arm that we spotted on the earlier prototype D.O.S.S posts, a location that should be less prone to contamination from spray thrown up from the rear tire. Accessing the cable anchor bolt looks to be infinitely easier than most other layouts, and the post is also reversible, letting the rider mount the cable on either the left or right side of the post depending on what best suits their bike.
Ball Bearing Internals
The D.O.S.S's internals are like nothing currently used within a telescoping post. Eight stainless steel ball bearings are employed, rolling on three different length grooves - one for each of the three height options - that have been machined into the inner wall of the main tube. The eight ball bearings are captured at the bottom of the inner tube (or stanchion), with them being pushed outward by the locking cam (the flanged piece at the far left in the photo above). In the locked positioned, the largest diameter of the cam pushes all of the balls out and locks them into the groove.
When pushing the short lever to move the post to the ''Trail'' position, the cam moves half way in its travel, with the four pockets machined into it allowing four of the ball bearings to come out of the grooves and drop into the pockets. The four remaining bearings sit in a linear groove that correspond with the 'Climb' and 'Trail' position, allowing the post to lower to the 'Descend' position when the lever is pushed. Releasing the lever allows the cam to force all eight of the balls to expand out and lock into groove.
Pushing the larger lever allows all eight of the ball bearings to move inward, letting the post stroke through the entire length of its travel. The post is also still functional if an air seal fails, or you manage to snap a cable, by manually moving the actuation arm.
| A look inside the D.O.S.S. reveals a complicated system of cams, keyways, and ball bearings.|
Self Adjusting Steel Keys
The exploded view above gives you a look into the inner workings of the D.O.S.S. seat post, with the one piece forged upper tube at the top (unfinished and cut in two
), and a cutaway of a fully assembled D.O.S.S. post at the bottom. Four stainless steel keys are forced outward by the keyway cam and four ball bearings, keeping the post's stanchion from rotating. When the post is locked into position the cam forces the bearings outward, pushing the steel keys into four grooves that have been machined into the inner wall of the tube. Pushing the remote lever to move the post up or down also shifts the keyway cam, allowing the keys to relax inwards and the post to go through its travel. This design means that there is very little friction from the keys when the post is going up or down, simply because the keys have retracted when the lever is depressed.
The keyway cam is a different unit from the locking cam, and has been designed to have no free play. The cam will push the keys out slightly further as they or the grooves wear, meaning the the system should be self adjusting.On The Trail
Our D.O.S.S. post was one of the first to come off of the production line (as opposed to being assembled as a prototype
), so we were eager to find out how it functioned in the real world. That real world, unfortunately, consisted of just two days worth of saddle time - not enough for us to comment on the post's reliability, but sufficient time to report back on its general function. Pushing the lever allows the post to cycle up or down, as you'd expect it to, but it was the D.O.S.S.'s smoothness that surprised us. There felt to be next to no resistance throughout the stroke, due in large part to the steel keys retracting as the lever is pressed. The low air pressure, set only between 10psi and 25psi to adjust return speed, also let the saddle lower quickly under our body weight. Unlike some other air sprung designs, the D.O.S.S. doesn't slow its descent as you near the end of the stroke - the force required to lower it feels the same at the end of its travel as it does at the top. It clearly will require more force due to the air chamber shrinking in size as the post lowers, but the low starting pressure makes the change unnoticeable.
Return speed was quick enough that we never found ourselves wanting it to be faster, but it wasn't so fast as to make us worry about causing bodily harm to vital organs. We also appreciated the post's audible 'klunk' when it raises back to either the 'Trail' or 'Climb' position, letting us know that it was exactly where it needs to be. While that may sound trivial, we've often found ourselves second guessing the saddle's position when using a silent telescoping seat post. This isn't going to be an issue with the D.O.S.S.
So, just how handy did we find the remote's second lever? Very much, as it turns out. Hitting the smaller, black lever does just as FOX claims - the post can only drop down 40mm to the 'Trail' postion, or return back up to full height. There was no searching, no having to weight the saddle longer than we wanted to in order to lock it down into the middle setting; just hit the black lever and it quickly lowers to the desired height. Is it worth the added complication? The jury is still out on that point given that we'll need much more time on it before making that call, but we also have to wonder if the D.O.S.S. makes more sense than an infinitely adjustable post.
| The D.O.S.S.'s remote isn't like anything currently used to operate a telescoping post.|
The D.O.S.S. cycled smoothly through its travel, and we can see a lot of riders being fans of the remote's dual lever that allows you to easily find the 40mm drop setting, but the large presence of said remote is gigantic compared to trimmer offerings from the competition. We also didn't find it terribly ergonomic, although we didn't get to spend as much time setting it up as we would have liked. An under-the-bar setup looks promising to us, although this will only work for riders who don't run a front derailleur, and we didn't get a chance to run such a setup during out short test session. There was also a small but noticeable rattle to the post, although it wasn't the usual side-to-side play that is common (but not noticeable when riding
) on many dropper posts. Instead, it was actually a small vertical rattle that could be easily heard when the saddle was jiggled by hand. No, we couldn't feel or hear it while riding, and we realize that there must be a small amount of free play present in order for the post to cycle up and down freely, but its worth noting regardless. The D.O.S.S. is a very interesting seat post option, one that is different enough from the competition that it just might offer an advantage. On the other hand we can see the post's dual lever remote making or breaking the post in many rider's eyes, especially those who are used to an infinitely adjustable post. Reliability will be key to the D.O.S.S.'s success given that the general consensus is that most telescoping posts fail in that regard. Stay tuned for a longterm review where we'll address this concern.ridefox.com