Adjustable Seatposts – Three Way Test – crankbrothers kronolog, FOX D.O.S.S., RockShox Reverb

The not-so-minor details


crankbrothers kronolog, FOX D.O.S.S., RockShox Reverb


Within review


493g - $429.00


535g - $399.95


620g - $399.95


Within review


Within review

Some people would argue that the adjustable seatpost is one of the greatest recent advancements in mountain biking.  Whilst not being a new technology, it has only been in the past few years that the larger manufactures have started producing them in ernest.  Much to the joy of those who used to frequently dismount and adjust, the adjustable seatpost makes the transition from riding uphill to bombing downhills much easier.

Flow took three of the more popular posts from crankbrothers, FOX, and RockShox, and tested them for 6 months. Read on to see what we thought of each.

FOX D.O.S.S. (l), crankbrothers kronolog (c), RockShox Reverb (r)

crankbrothers kronolog

Inside that little box is where it all happens with the kronolog, a unique mechanism holds the seatpost in position.

The crankbrothers joplin post was the first widely adopted adjustable post, but like many pioneering products it certainly had its issues on the reliability front. Enter the kronolog, a completely new take on the dropper post from crankbrothers.

The most obvious difference between this post and the others in our three-way test is that the cable is routed to the body of the seat post, rather than the seat post head. This looks far cleaner, and means you don’t have a big loop of cable dangling between your legs when the post is dropped. Neat-o.

Also neat is the remote lever. Ours is tucked neatly under the bar where you’d normally find a front shifter, easy to activate and with plenty of adjustability to get the position just right. The action is nice and light.

The kronolog is infinitely adjustable and it relies on a mechanical system to lock the post at whatever height you set it. The front and rear surfaces of the sliding portion of the post are covered with hundreds of little ridges; when you release the lever little ‘jaws’ inside the post lock into these ridges to prevent the post from moving.

Setup is critical – there needs to be at least 3mm of free play in the lever throw before it begins pulling the cable. If there is too much tension on the gear cable, the little jaws may not engage properly and this can lead to the post slipping, which in turn will wear out the knurling on the post, exacerbating the problem.

We carefully obeyed these instructions from the outset and this has prevented any serious problems. Still, we have found that the post does slip slightly, tending to drop about 5mm from full extension when you sit on it. So far (after about six months of use) the problem hasn’t become noticeably worse, but the wear to the knurled surface of the clamping surfaces is clear and it doesn’t look too good for long term durability. Dirt can get past the seal easily, so the mechanism needs to be cleaned and lubed after wet rides. Fortunately this is easy to do, as is replacing the cable.

Out of the box, the kronolog has 125mm of travel, but for our frame that was too much. Luckily the post is supplied with a chip that drops the travel by 25mm, making the post more compatible for shorter riders or bikes with long seat tubes. Installing this chip to lower the travel was a ten-minute job and didn’t require any fancy tools beyond a pin spanner.

We do have a gripe about the seat clamp… it is very hard to make small adjustments to the seat position – we need to really whack the seat to get it to move.

All up, we feel like the kronolog has some ground to make up on the competition. The design concept is great, but the durability and execution aren’t 100% yet.

Weight: 493g
Size Tested: 30.9
RRP: $429
Contact: JetBlack Products (

The internal section of the seatpost is constantly being lubricated, but the seal isn’t tight enough to stop the greasy section of the post from attracting dirt and debris. It didn’t take long for messy buildup to occur.
The two steel claws retract from the flat surface of the inner section to allow the air spring, or your body weight to make the adjustments.
Small adjustments to the seat position were tricky with this clamp, not our favourite.
Careful setup of cable tension is vital.


Climb, Trail or descend. The D.O.S.S. offers three positions of adjustment and very fast operation.

Was the product department at FOX drinking when they named their first adjustable seatpost? We’re used to more robotic part names from FOX, like TALAS RLC, or Float RP23. But FOX’s first seatpost is named D.O.S.S., which is actually an acronym for Drops On Steep Shit. It made us laugh, anyhow.

We’ll be honest in saying we hoped for more groundbreaking features when we heard that FOX were releasing a dropper post to take on the likes of Crank Bros and Rockshox. The D.O.S.S didn’t set the world on fire with new technology – it wasn’t particularly light and the cable actuation was nothing new – but word quickly spread that the D.O.S.S. was a serious contender for the most desired post, with the durability and ease of operation impressing the skeptics.

The D.O.S.S. is actuated via a remote and cable, which enters the post from the side of the seat clamp. You can simply rotate the post to suit your bike’s cable routing. The remote lever is also ambidextrous (unlike the Reverb) and has adjustable reach to allow users to customise where is sits on the handlebar.

The very large remote lever is a real point of contention, and may turn users off with its bulky appearance. It is way bigger than any of its competitors, but it wasn’t the end of the world for us. Our test bike runs a single chain ring, so we were able to run the lever under the left side of the handlebar, where the front shifter would normally sit. In this configuration the lever was concealed nicely, and out of the way. If you do run a front derailleur, the lever must sit atop the bar where it sticks out like the proverbial dog’s bollocks.

What sets the FOX post apart from the other two on test here is that the three-stage height adjustment. Rather than offering infinite adjustment, there are three preset positions, designed to match the FOX CTD suspension system (Climb, Trail and Descend). There’s full height, a 40mm drop, and all the way down. If you hit the black part of the thumb lever the saddle drops by 40mm and will stop there. If you hit the main silver lever it will drop completely.

This preset system makes for much faster changes in seat height; you know exactly where the saddle will be, rather than having to guess how far you’ve dropped it. We found that 40mm is the perfect drop for rough trails, most descents, and all but the steepest of roll-downs or jumps.

Setup with the FOX post was the simplest of the three on test, and after six months of solid use it feels just like it did on day one with no unacceptable play or unwanted movement. It does make a small knocking sound when you sit on the seat, and this can be noticed when climbing if you lift weight on and off the saddle. It wasn’t a real issue for us though, and we’ve certainly grown to accept that adjustable posts will always have movement in them; just some are slightly better than others.

The twin bolt seat clamp makes for very easy and no fuss saddle fitment and adjustment, and the quality of craftsmanship in the clamp is very neat and reflects FOX’s top-end status.

The FOX is the heaviest on test and the big remote lever is impractical in some ways, but the speedy actuation, smart finish, good aesthetics and very sturdy construction (and the name) make us smile.

Weight: 620g
Size Tested: 30.9
RRP: $399.95
Distribution: Sola Sport (

Close inspection reveals some very nice attention to detail, and clean craftsmanship of the mechanism and clamp.
By spinning the post 180 degrees and flipping the seat clamp parts around too, the cable can be routed to enter on both sides if need be.
Hit the black lever to drop it 40mm, or all the way with the silver. It’s a big lever, no doubt about that.
FOX provide a neat cable guide to help the cable track in a straight plane when fully compressed.

RockShox Reverb

The benchmark in adjustable seatposts. The Reverb uses hydraulics for smooth and infinite adjustability.

RockShox have a couple of variants of their very successful Reverb post available. There’s the standard Reverb (on test here) and the Stealth version, which uses a hose routed internally to activate the post from inside the frame, meaning there are no loops of hose dangling off the seat post head.

While the other posts in this trio of droppers rely on a gear cable, the Reverb is a hydraulic system. This has advantages – there is never a problem with grit or mud fouling the cable, and cable routing doesn’t matter at all – and disadvantages – the system needs to be bled like a hydraulic brake upon installation. This involves a syringe and 2.5wt fork oil, but it’s not beyond most backyard mechanics.

Early versions of this post were as reliable as a 1980s Alfa Romeo, but the last couple of years have seen huge improvements and our post has been flawless.

In all conditions it has remained smooth and leak free, requiring no maintenance whatsoever.

The Reverb’s ergonomics are great, especially if your run SRAM shifters and Avid brakes. Using the Match Maker clamp you can integrate the Reverb lever, brake and shifter into single clamp for supremely clean bars. We also appreciate the traditional dual-bolt micro adjust seat clamp; simple and reliable.

Like the kronolog, the Reverb is infinitely adjustable too, with 125mm of travel on our particular post, though a 150mm-travel version is available too if you really need to get your seat outta the way. Return speed to full height is slower than most posts – you can adjust how fast the post comes back up via a dial on the remote lever, but even on its fastest setting it’s a little bit laggy.

There’s a little bit of play in the post at full extension, both twisting and fore/aft, but you honestly don’t notice this on the bike and it’s greatly reduced when the post is dropped into its travel.

Weight: 535g
Size Tested: 30.9
RRP: $399.95
Distribution:  Monza Imports (

Push the button and away it goes. RockShox offer left and right options, and with a SRAM shifter and Avid brake, all components are able to be integrated very neatly with one single handlebar clamp.
A little bleed port sits up under the seat rails, and the clamp gives fuss-free saddle adjustability.
Return speed of the post is adjustable, but still not as rapid as the FOX or Crankbrothers.
The latest generation of Reverbs are most definitely more reliable and ours has been peachy.

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