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Gamux Sego Gearbox DH Prototype Switches to Belt-Drive

gamux sego belt drive gearbox downhill bike prototype fort william 2023 bds
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Last week, Gamux Factory Racing made the trip from Switzerland to Scotland, to race Round 2 of the British Downhill Series in Fort William. They were in good company; the Santa Cruz Syndicate, Madison Saracen Factory Racing, Commencal Muc-Off, Nukeproof Factory Racing, and Canyon Collective FMD all rocked up on Aonach Mòr to get some invaluable time on the track that will crown the 2023 Downhill World Champions.

Gamux Factory Racing Team riders, Lino Lehmann and Mike Huter, came equipped with an updated prototype from the Swiss manufacturer, a prototype that stood out in the crowd not just because of the belt-driven Pinion gearbox it was sporting. Thanks to its construction, the CNC-machined frame has a rather unique aesthetic about it, particularly at the swingarm.

The stealth frame, unusual choice of drivetrain and beautifully machined links and idler pulley had us rocking up at the Gamux Factory Racing pits to learn more about the bike from Mechanic and Sporting Director, Romeo Cairoli. Sadly, detailed photos were not yet allowed.

gamux sego gearbox belt drive prototype dh bike raced fort william bds 2023
The prototype Gamux Sego frame is said to weigh 4 kg without the Pinion gearbox

Gamux Sego Belt-Driven Gearbox Downhill Bike

The Gamux prototype in question is named the Sego, an Old Celtic word meaning “to win” or “winning”. With intentions clearly set out, Junior rider Mike Huter did his utmost to achieve that goal, sending it into P2 on Sunday with a time of 4:42.523. That’s a way off Henri Kiefer’s winning time of 4:36.476, but still very admirable in the context of this being Mike’s first race down the infamous pinball-like rock gardens of Fort William.

The Sego piloted by Mike and Lino last weekend is a further development on the bike that was raced by the team last season; it is said to have the same geometry and kinematic, but some big changes in the manufacturing process, and the linkage design, are said to have increased its bike’s overall stiffness considerably.

The bike has undergone something of an overhaul since last season. It is still a linkage-driven single pivot, with a layout not vastly dissimilar to that seen on the Nukeproof Dissent, but the swingarm has a wildly different construction featuring triangulated struts, presumably to deliver high strength and stiffness properties while also helping to keep weight reasonable. The new swingarm design was necessary to accomodate the belt drive.

Incidentally, Specialized’s prototype DH bike also spotted last weekend sees a similar triangulated architecture on its chainstay.

gamux sego belt drive gearbox downhill bike prototype fort william 2023 bds
Gamux glue a secondary alloy tube into the frame’s seat tube. From a technical standpoint, they say it’s not so easy to hollow out the solid seat tube to a depth required for insertion of a seat post, so an extra tube is inserted afterward.

Gamux DH Prototype Kinematic

Gamux remain tight-lipped on key details around the frame’s geometry and construction but Founder, Romeo, and Frame Designer, Pascal Tinner, were happy to answer some of our questions around the kinematic.

Tinner informs us the kinematic is relatively unchanged since last year’s iteration of the Sego. The leverage curve of the its 200mm rear wheel travel sees an overall progression of around 27%. On this prototype, the front shock mount is interchangeable to allow riders to find the right level of progression in the linkage, but this aspect is likely to be fixed on the production frame.

The rear axle tracks a rearward path for about 100mm, before arcing forward again to the full 200mm. At bottom-out, there is no net change in effective rear-center length. Thus, Gamux consider the linkage to be of the mid-high pivot flavor.

On this prototype, Gamux are still experimenting with different idler pulley configurations, but on the bike you see here, anti-squat is said to be around the 100% mark at sag, while anti-rise values are described as “pretty” at sag.

Belt-Driven DH Bikes are now UCI-Approved

Obviously, a major change for this season is the switch from a gearbox with a chain drive, to a gearbox with a belt drive. Wording of the UCI regulations on this topic was updated on the 1st January 2023; downhill mountain bikes can now be either chain-driven or belt-driven. Before this date, the UCI permitted only chain-driven mountain bikes to compete in downhill.

Romeo tells us the Gates belt-driven option was always the brand’s preferred option, ever since they first partnered with gearbox manufacturer, Pinion. The prototype raced at Fort William runs the Pinion C1.6 Gearbox, with 6 gears delivering a 295% gear range. The gearbox can be configured with a grip- or paddle-shifter; Gamux has unsurprisingly opted for the latter on this DH bike.

gamux sego belt drive gearbox downhill bike prototype fort william 2023 bds

At this stage in the bike’s development, Gamux is still able to swap out the swingarm dropouts to allow the riders to choose between a 27.5″ or 29″ rear wheel; for Fort William, both Lino Lehmann and Mike Huter opted for the full 29″ set up.

When can you order one?

We are told the Gamux Sego is due for production at the end of this season. Two sizes are set to be available, one of which will boast a reach of 485mm. That won’t be fixed, however; the Sego will run a 56mm headtube to allow for use of reach-adjust headsets.

In terms of innovations, the Gamux Sego is one of the most interesting downhill bikes under development right now. We;ll be keeping an eye out for any further evolution of the bike this season, and keeping readers updated throughout.


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Nasir Munir
9 months ago

Wow! This is something really new to my knowledge. I wasn’t expecting this type of innovation anytime soon.

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