FOX's new 620 gram D.O.S.S. (for 'Drop On Steep Shit'
) telescoping seat post features either 100 or 125mm of mechanically controlled travel, as well as a 40mm drop 'Trail' position for rolling or technical terrain that still requires pedalling. The D.O.S.S. is part of FOX's 'CTD ride dynamics system', which refers to three distinct phases of riding: Climb, Trail, and Descend, with the post's three height postions - full height, 40mm drop, and fully dropped - corresponding to the CTD acronym. FOX has designed an interesting dual lever remote, with the smaller paddle only offering access to the 40mm drop 'Trail' position, in an effort to make finding the middle setting easier on the trail. The post uses a standard shift cable to control its mechanical internals. Our 125mm drop test model features a minimum insertion to saddle rail clamp height of 290mm, and measures 190mm from maximum insertion (bottom of the top cap
) to the saddle rail clamp. Both numbers were measured with the post at full height.
The Details Dual Lever Remote
The cable operated D.O.S.S. features mechanical internals and a low pressure air return spring, as well as a novel dual lever remote that simplifies finding the post's middle height position.
FOX D.O.S.S. details:
- Mechanical internals
- Air return spring (10 - 25psi to adjust return speed)
- Three postions: full height, 40mm drop, fully dropped (Climb, Trail, Descend)
- 100mm or 125mm of total drop
- Two-bolt saddle rail clamp
- 30.9mm or 31.6mm sizes
- 620 grams (post, lever, hardware, cable and housing)
- MSRP $439 USD
The D.O.S.S. is the first telescoping post on the market to utilize a dual lever remote setup, with the shorter lever restricted to activating the post's 40mm drop 'Trail' position, and the larger lever letting the user run through the post's entire stroke. Why would FOX go this route? If you've ever spent time on any of the numerous mechanically operated posts that feature a secondary, slightly dropped seat height postion, you know that it can sometimes be tricky to find that middle setting. Struggling to position the saddle correctly while in the heat of the moment is the last thing a rider needs when approaching a tricky section, and the D.O.S.S. looks to remedy this.
The larger, outboard paddle (silver) allows you to use the post's entire travel, including stopping at the 'Trail' position. The remote's smaller, inboard paddle (black) restricts movement to the 40mm drop 'Trail' postion.
Pushing the large silver lever allows you to stroke through the post's entire 125mm of drop, including stopping at the 'Trail' postion that is ideal for fast, rolling terrain where you want a bit of extra clearance, but still need to pedal. The inner black lever will only allow the seat post to drop to the 40mm 'Trail' setting, a system that should make searching for the middle position a thing of the past. 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, and it also employs a hinged clamp for easy removal.
Ball Bearing Internals
A view of the bottom of the remote shows the three fore/aft position options.
The D.O.S.S's internals are like nothing currently used within telescoping posts. Eight stainless steel ball bearings roll 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 bearings are captured at the bottom of the post's stanchion, with them being forced outward by a locking cam. In the locked positioned, the largest diameter of the cam pushes all of the balls out and secures them into the corresponding grooves.
The locking cam is the flanged component on the far left of the rod. Notice the machined, angled pockets that either push the bearings out or allow them to retract.
When pushing the short lever to move the post to the 'Trail' position, the locking cam moves halfway through its travel, with four pockets machined into it allowing four of the bearings to move out of the grooves and drop into the pockets. The four remaining bearings sit in a linear groove that correlates with the 'Climb' and 'Trail' positions, allowing the post to fully lower to the 'Descend' position when the larger lever is pushed. Releasing the lever allows the cam to force all eight of the balls to move out and lock into the groove. Pushing the larger lever lets all eight of the ball bearings move inward, letting the post stroke through the entire length of its travel. The D.O.S.S.'s mechanical internals mean that the post should still function if an air seal fails, or you manage to damage the cable or the remote, by manually moving the actuation arm on the side of the post's head.
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 act to keep the post's stanchion from rotating, with each one being forced outward by both the keyway cam and four ball bearings. The cam forces the bearings outward when the post is locked into position, pushing the steel keys out into four grooves 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. The layout 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. This, combined with the post actually rolling through its travel on the ball bearings, mean that it should move very freely when activated.
The keyway cam is actually an entirely different unit from the locking cam, and has been designed to have no free play. The system has also been designed to be self-adjusting, with the locking cam pushing the keys out further as either the grooves or the keys themselves wear over time. Installation and Setup
Setting up the D.O.S.S. post is a piece of cake. The two-bolt saddle clamp is easy to work with, and the remote's hinged clamp means that you don't have to remove any controls to install it. The remote can be configured to fit either above or below the bar, as well as on the left or right side, simply by loosening a single bolt. There is also a three position fore/aft adjustment that allows you to tune its position to best fit your hand. We initially began with the remote on the top of the bar, on the left side, but swapping the position is so easy we ended up changing it while on the trail. Because we're using SRAM's Grip Shift, we are able to run it underneath the left side, a setup that won't play nice with trigger shifters.
The actuation arm is positioned at the side of the post instead of the more common location at the rear, and can also be swapped from right to left simply by flipping the seat rail clamps by 180 degrees. 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.
Our D.O.S.S. arrived with 25psi in the air return spring, which is the maximum recommended amount. It rebounds quite fast at this pressure, with a very audible top-out noise to let you know that it's at full extension. We dropped the pressure down to about 15psi, which enough to still have the D.O.S.S. rebound quickly, but in a more controlled manner. The top-out 'clunk' was still present, which we far prefer over completely silent action.
The post's side-mounted actuation not only makes for smoother cable routing, but also means that you don't have to tilt, or even remove, the saddle to access the clamping bolt. This small detail was greatly appreciated given that clamping the cable requires moving the saddle on nearly every other cable operated dropper post we've used. Adjusting cable tension on the D.O.S.S. is easy via the remote's barrel adjuster, with two full turns making a big difference in the post's action. Too little cable tension and we found that the post had trouble lowering past the 'Trail' postion, hanging up slightly before lowering further. Turning the barrel adjuster counterclockwise a few turns, adding cable tension, eliminated this. Too much tension resulted in the post knocking up and down slightly, or even moving on its own if tension is excessive. Interestingly, the D.O.S.S. has a small amount of vertical play to it even with the cable undone, something that we were never able to remove from the system. Performance
The funky looking D.O.S.S. remote had many riders asking us what was going on, but we have to admit that the dual lever design has major merits on the trail. Pushing on the smaller, inboard lever left no question as to if the post would find the 'Trail' position - it will simply only drop to that height. Contrast this to other designs that have left us searching for their middle settings, even after many miles of getting used to them, and we can see why FOX went this route. The remote also proved to be quite resilient despite its vulnerable looking position when mounted above the handlebar - it shrugged off quite a few crashes, as well as us flipping the bike over to perform trail-side repairs. We have to eat some humble pie here because we originally took issue with the remote's design, but the dual lever setup makes complete sense in use. Having said that, its ergonomics are a bit strange, with the paddles sitting at a bit of an odd angle for us. We never really found a position that we were completely happy with, despite the three fore/aft positions to pick from.
Required lever effort is about on par with anything else on the market, although we'd say that the long paddles should help over come the friction of a contaminated cable. The effort does increase for either lever if the seat has your full body weight on it when when you push them, but it isn't enough to be a deal breaker in our books.
The D.O.S.S. is incredible smooth throughout its travel, moving up and down with what feels like zero resistance, and making other posts feel sticky and slow in comparison. This is down to its ball bearing internals - the stanchion actually rolls up and down - and the post's low return spring air pressure of between 10 and 25psi. The action is remarkably effortless, and has remained so throughout our time on it. The air spring feels very linear as well, with us never having trouble fully lowering the saddle during those split second moments when the front tire is rolling over the edge of a precipice. When the paddle is pushed to raise the saddle back up, it happens rather quickly. The D.O.S.S.'s undamped rebound stroke is very similar in speed to Specialized's Command Post, with it returning to full height with zero hesitation. We view this as a plus, with it coming back up quickly and consistently when needed. This is especially helpful when navigating tight climbs and descents, as the return speed and very audible top-out noise left us with no doubt that the saddle was at full height once again. Finding the 40mm drop 'Trail' position on the post's upstroke could be tricky, so we usually resorted to bringing the post to full height and then pushing the 'Trail' lever to lower it part way back down.
The comparisons between the D.O.S.S.'s set three positions and an infinitely adjustable post are inevitable, and there will no doubt be many riders who are happy with the post's fully dropped and 40mm drop 'Trail' positions, but we couldn't help but find ourselves wishing for more range from time to time. It could be that our technical local terrain made the 40mm drop middle setting feel a touch tall (45 - 50mm seems like it would be ideal, but that's just us
), or that we missed being able to drop the saddle only by 10 or 20mm for a steep, technical climb that had us spooked about high-siding off the edge of the trail, but we still prefer the ability to set our saddle height exactly
where we want it.
The ambidextrous remote can also be mounted above or below the bar, with us far preferring the latter option. Keep in mind that trigger shifters would keep you from mounting it below the bar, though.
When FOX debuted the D.O.S.S., many riders showed their surprise that it didn't feature a stationary actuation point on the lower tube. While we admit that we also questioned the positioning on the seat post's head (after all, why not eliminate one of the biggest hassles concerning dropper posts?
), we were amazed to find that the location on the side of the post's head made a huge difference when it came to cable management. Yes, there is still a loop of surplus cable when the D.O.S.S. is lowered but it seemed to be far easier to deal with, staying off to the side of the bike instead of looping straight out the back to buzz on the rear tire. We also commend FOX for employing a two-bolt saddle rail clamp that is immune to tilting, regardless of how hard you come down on the back of the saddle. Sure, a single-bolt, clamshell design might be a touch lighter, but a two-bolt setup is really the only way to go.
The D.O.S.S. lets riders choose from a fully extended 'Climb' position, a 40mm drop 'Trail' position, and a fully dropped 'Descend' height.
The D.O.S.S. proved to function very well on the trail, but the FOX dropper has a few quirks that we'd like to see addressed before we'd call it ideal. Our chief gripe concerns the small amount of vertical free play in the post at each of the three positions. While the play really only boils down to one, maybe two, millimeters, the knocking noise emanating from the movement turned out to be very annoying. It never got worse from new, but we found it to be disconcerting when we were concentrating on the trail ahead of us.
Our only other issue centers on the rather sizeable remote unit that, while fitting nicely between the other controls on the bar, is about as far from integrated as possible. When mounted atop the bar, it sits much higher than any of the other controls, not to mention that flipping your bike over to repair a flat will see it resting directly on the ground. It is much more incognito when mounted under the bar, though, which is where we preferred to attach it. Besides the questionable aesthetics, the remotes ergonomics are a touch off. The levers felt to be at a bit of an odd angle for our hands, with us consistently wishing for some type of rotation adjustment on the remote head that would keep us from having to reach so far with our average sized thumbs. Pinkbike's take:
|Where does the D.O.S.S. sit in the dropper post hierarchy? Does it dethrone the Reverb for top honours? There is no doubting that the FOX post is a top quality unit - just look at its Swiss watch-like internals - but the post's odd rattle and slightly-off remote ergos detract from its great action. Having said that, the novel dual lever setup scores it major points, though, with it eliminating having to hunt for that middle seat height, and its incredibly smooth travel does make all other dropper posts feel as if they've left underwater for a few weeks. If FOX can remedy the two points of discord mentioned above, we'd have to say that there would be a new boss in town. - Mike levy|