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Funn UpDown Internal drops in on non-IFP mountain bike dropper seatpost – Updated

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Funn kicks off the morning Sea Otter releases with a unique new UpDown Internal Dropper. They had an IFP-based UpDown dropper post in the lineup since 2016, but when it was time to go internal routing, they also developed a new Twin Tube Cartridge design that avoids the pitfalls of IFPs.

Funn UpDown Internal non-IFP dropper seatpost

We’ve looked at the issues with Internal Floating Pistons before. While they work well when new and are cheap to produce, IFPs tend to suck air into their hydraulics over time, leaving a squishy post that needs a replacement cartridge. We saw BikeYoke overcome the problem with a manual reset, now Funn may have an even easier solution.

Their new Twin Tube Cartridge design actually features a mechanical reset of the dropper post cartridge that happens automatically every time you use it. Drop the post down and it automatically separates oil and air, eliminating the sagging dropper issue while still getting IFP-like smooth action.

Twin Tube Cartridge, non-IFP design and development

The way they describe it:

The cartridge has an outer and inner tube that contains compressed air and hydraulic oil. When the actuator is in a closed position, the seatpost is locked in place. At this point the hydraulic oil contained in the inner chamber supports the rider’s weight.

When the actuator opens and dropper compresses, oil flows from the inner chamber to outer chamber, and compressed air enters the upper part of inner chamber. At full compression, the piston [pushes] both hydraulic oil and unwanted air from the inner tube.

When the cartridge rebounds from full compression, compressed air pushes the piston shaft upwards. Only the [lower] hydraulic oil gets sucked into the inner chamber. This way the cartridge can effectively reallocate both air and oil back to its proper designated locations in the system.

That ability to self-separate oil and air means it should retain full functionality overtime, even as flex around the seals & slider could allow bit of air and oil to move back and forth from their proper locations.

Of course a new cartridge design means a lot of testing is needed. So Funn partnered with the company who produces them (from the auto sector) to both fine tune the dropper’s rebound & compression forces, and to run the post through a tough 30,000 cycles of torture testing. At the end of that, they say it came up with no decline in performance and no saddle sag.

Tech details

The UpDown Internal dropper uses a one-piece forged 7050 aluminum inner tube with a hard anodized coating for long life & smooth actuation, and features a 2-bolt saddle rail clamp.

The new dropper is available in both 30.9 & 31.6mm versions, and in either 125mm or 150mm of travel. A 30.9x125mm post claims a weight of 550g, plus another 50g for the remote.

The UpDown Internal also gets a new 4-way adjustable trigger remote to work on either side of the bar, on top or down below.

The new lever features more leverage for easier operation and can now be infinitely adjustable to get your ideal angle of the paddle just right. It can also be paired with a SRAM Matchmaker clamp while still retaining angle adjustability.

No word yet on pricing or availability. Update: The 125mm travel Funn UpDown dropper retails for $259, and the 150mm version for $279.


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