When Gerard Vroomen and Andy Kessler launched Open Cycles back in 2012, they wanted to push the limits of lightweight and stiffness on mountain bikes. And their original Open 1.0 did a pretty good job of kicking things off. Then they released a special edition AXX1 model and others that brought the complete bike weights lower thanks to a very, very expensive builds.
Now, they’ve gone back to the frame to eek out a bit more performance and shed a few more grams. The new Open One will be made in Germany using a new layup process and unusual frame details. The result is a frame that comes in as light as 796g for a Large…
One of the biggest visual changes is the dropped drive side chainstay. This layout let them improve clearance for the chainrings and tire without having to use an overly tall tube shape. They say it provides all the stiffness they want with minimal material. From there, the chainstays flatten slightly to work with the bowed seatstays to improve vertical compliance.
The seat tube was slimmed down a little, then vertical ribs were added to the sides to prevent lateral flex and reduce the likelihood of buckling. The slimmer size better fits the slightly narrower PFBB30 bottom bracket. Before, they used BBright since it provided an ultra wide and very stiff platform. Thanks to an extended BB shell that creates a thick bridge going back to the chainstays, they maintained stiffness while making a frame that’ll work with many more cranksets.
Out back, they switched to a very slick thru axle. The threaded end doubles as the mount for the rear derailleur hanger, keeping the overall weight the same as with QR but much stiffer.
Part of the reason for moving production to Germany was access to premium pre-preg fibers. They wrapped hi-mod UD fibers from the top and down tubes around the head tube. The woven fibers are a lower mod (but not lower quality) with what they say are very high end resins. These provide the necessary strength while the high mod stuff improves stiffness.
All in all it’s a very good looking frame. Production weights are simply claimed as “under 850 grams”, which pushes the boundaries of light weight for mountain bikes. Some of what you’re seeing here can also be considered a teaser for a (near) future full suspension bike. Droooooool.