Turnon Components Bunker Seatpost

We first started coming across Turnon Components at trade shows a couple of years ago, intrigued by their use of a submerged dropper post as part of their exhibit. The point of the display was to showcase their “water and dust proof” dropper post, aptly named the Bunker. What sets this post apart from others is the lack of any kind of venting holes at the bottom of the post, which essentially creates a second air chamber inside the post as the air compressed by lowering the post has nowhere to go. To see what all this translates to in real life, we’ve been testing the Bunker for a few months now and we’re here today to provide our report.

Turnon Bunker Highlights

• Fully sealed, dual air chamber design (water proof and dust proof)
• US patent granted in October 2024 on the internal mechanism and design
• Self-bleeding hydraulics
• User serviceable
• 400-hour recommended service interval
• Internal cable routing compatible only
• Diameters: 30.9 and 31.6mm
• Stock travel options: 125, 160, 190mm
• Travel adjustable in 5mm increments
• Weight: 552 grams (31.6mm/190mm, verified)
• Lever weight (with cable): 112 grams (verified)
• Three-year warranty
• MSRP (post only): $252.00 - $289.00 USD (depending on travel option)
• MSRP (lever): $55.00 USD ($39.00 USD when purchased together with the dropper)

Initial Impressions

The Bunker turns up in a fairly simple package, looking for all intents and purposes just like any other dropper post. Turnon included some service parts and a travel adjustment kit with our sample, these are all available to purchase directly via their website or through their network of dealers around the world. All the parts that make up the dropper are available as spares, which always bodes well for the longevity of your investment.

The Bunker is available in 3 different lengths and the two main seat post diameters (Turnon can supply a shim if your bike features a 34.9 mm seat tube). The travel can be adjusted down in 5 mm increments, by a savvy home mechanic or a shop (it requires a tear down and rebuild of the internals). As for the dimensions, the Bunker is a little bit longer than its main competitors, something to take into account if you’re looking to really maximize the amount of travel you can fit into your frame. Here’s a table comparing it to some of its main rivals, you can see that in terms of stack height (“Collar-To-Rail”) it’s doing well, while the overall insertion length is significantly longer than a OneUp V3 for example. On the flipside, it will give you a lot of max extension, which might help if you have very long legs but don’t want too much drop.

The internals are what make the Bunker special. The airtight lower leg design creates an extra air spring, which Turnon uses to help overcome the stiction present in the top seal (which is purposely very tight, in keeping with the water and dust proof design brief). The hydraulics are of the self-bleeding kind, which basically means that any air bubbles that might form on the oil side of the piston are purged the next time that the post is compressed. The pressure in the main air chamber needs to be quite high, because it is actually what holds the rider’s weight up. The post will even allow a small amount of sag movement under heavy compression, which can be exacerbated by running lower pressure.

Turnon has just been granted a US patent for this design, which presumably means that it is different from other droppers in a significant enough way as to warrant the protection of the innovation. From the patent abstract: “While increasing a height of a saddle mounted above the hydraulic inner tube, pressure of high-pressure gas in the second gas chamber not only improves speed and fluency of the hydraulic inner tube being lifted, but also optimizes concentricity and side force resistance of both the hydraulic inner tube and the outer tube.” Interesting wording, as always in patents…

Turnon also supplies a remote lever, as an optional purchase. The lever is highly adjustable and can be moved around in several different directions as well as rotated, and it can also be mounted to SRAM's MatchMaker (using the original bolt). You can get the lever with either a black or silver finish.

On The Trail

Installing the Bunker was straightforward, with nothing out of the ordinary to report. The cable pull needed to operate the actuator is quite short at 6 mm, which means that the remote lever can make do with a fairly small main pivot barrel. It was easy to find a really good position for the lever, we particularly appreciate the ability to adjust the rotation of the lever around the main pivot as we find that a bit of “positive angle” towards the thumb at the start of the stroke makes for a very solid feeling of engagement as you press it.

The amount of force required at the lever is a little bit higher than some other droppers, as is the force required to compress the post itself. It’s not to the point of making it difficult to operate, but you can definitely feel the high pressure in the main air chamber as well as the tight seal. We ended up running a bit more pressure than recommended to give the Bunker a faster return speed, and we also found that a little bit of preload on the cable helps in this regard. After these adjustments, the return speed is about average – similar to a Fox Transfer V3 for example. There is a solid and fairly loud “clunk” at full extension, letting you know that the post is up there and ready for pedaling. You can press the lever while seated, and you can also pick the bike up by the post even with the saddle down, two aspects that are fairly important for a good dropper post experience in our opinion (it’s maybe not kind to the post, but life is sometimes hard for everyone yeah).

Once we found the sweet spot with the aforementioned adjustments, operating the Bunker became intuitive. The modulation is good, and it’s very easy to partially depress the lever to slow down the return speed to help with finding those half-mast cruiser positions. As for the “suspension” action we mentioned earlier, it happens on larger compressions during seated pedaling. There’s a tiny bit of give in the air spring that offers a degree of cushion and comfort in these situations. The post is absolutely not saggy, and there is no vertical play present, it’s literally like compressing an air spring with very high pressure in it. This phenomenon can be slightly accentuated with the post at half-mast, as there may be a bit more air mixed into the oil in this position. We found this extra cushion to be quite comfortable in those high-compression situations (picture pedaling uphill over a square rock with tired legs), and it was never to the point of bothering us (there is absolutely no play or sag during normal seated pedaling).

Things That Could Be Improved

There is a little bit of resistance when you lower the post, both from the hydraulics and the main seal it seems like. The result is a somewhat less slick feeling than a BikeYoke Revive for example, even though the modulation is excellent and the speed of operation is good. Aside from that, the base of the post is a bit longer than some competitors, so take that into account if your frame has limited insertion depth.

Long Term Durability

The Bunker features a design specifically developed to lengthen service intervals and to prevent any external contaminants from wreaking havoc on the internals. We’ve had our sample for 5 months now, with about 3.5 months of actual riding time, and we have not noticed any kind of air leaks or other performance degradation. The post is still working like when we first set it up, which bodes well for longevity. There was a very small amount of side-to-side play present out of the box, and that has not evolved at all at this point. There are spares available for every component of the dropper, and it's fairly easy to service for a competent home mechanic.

What’s The Bottom Line?

Dropper posts have come a long way in the last few years, in particular with regards to durability. It’s one of those components that gets little in the way of love, yet is expected to perform flawlessly ride after ride. With its sealed design and self-resetting hydraulics, the Turnon Bunker is attempting to push longevity to the next level, and based on our testing so far, it seems that it is working. Aside from the durability aspect, the Bunker also offers great ergonomics and a bit of extra “suspension” action during violent compressions, which can add a little comfort to your ride. All in all, the Bunker is one of those products that comes a bit out of left field but makes a lot of sense once you’re out on the trail.

More information at: www.turnoncomponents.com.

About The Reviewer

Johan Hjord - Age: 51 // Years Riding MTB: 19 // Weight: 190-pounds (87-kg) // Height: 6'0" (1.84m)

Johan loves bikes, which strangely doesn’t make him any better at riding them. After many years spent practicing falling off cliffs with his snowboard, he took up mountain biking in 2005. Ever since, he’s mostly been riding bikes with too much suspension travel to cover up his many flaws as a rider. His 200-pound body weight coupled with unique skill for poor line choice and clumsy landings make him an expert on durability - if parts survive Johan, they’re pretty much okay for anybody. Johan rides flat pedals with a riding style that he describes as "none" (when in actuality he rips!). Having found most trail features to be not to his liking, Johan uses much of his spare time building his own. Johan’s other accomplishments include surviving this far and helping keep the Vital Media Machine’s stoke dial firmly on 11.

Photos by Johan Hjord and Nils Hjord