Earlier this year I had the chance to meet Michi and Pascal from Brotlos Design. They both have an engineering background and work for Swiss engineering companies, and when they find time, they meet in their workshop and create wooden furniture and lamps.
As they both got more and more into mountain biking, they decided to stray away from woodworking and build their own bike. They were fascinated by the Kavenz Youtube video series
and the design of the bikes, so they got in touch with Giacomo from Kavenz. Under the condition that they don't make the frames commercially available, they got permission from Kavenz to build their own steel frame with 3D printed parts, which is based on the Kavenz suspension design.
While Michi and Pascal designed the 3D printed parts (made by Ecoparts), the frame was brazed by Stefan from Scarcycles. It comes in at around 3.7 kg (without shock) and the tubing is Reynolds 853.
The dropouts as well as the bearing seats for the chainstays and the seatstays are made using additive manufacturing; the material is high performance tool steel 1.2709 (maraging steel). The AM Rocker is made from Ti-6Al-4V titanium alloy.
In order to keep the costs low, they went for a secondhand SRAM Eagle drivetrain and Fox suspension. When we took the photos, they were running a Fox DPX2, but in the meanwhile they replaced it with a RockShox Super Deluxe Ultimate (love the name) coil, which has improved the performance a lot according to Michi and Pascal.
To get some light wheels and lots of grip at the same time, Michi and Pasci went for Pirope A.30 wheels with "heavy but awesome" Michelin Wild Enduro tires. The Shimano XT four-pot brakes are basically maintenance free and just work.
A Renthal Fatbar 35 is clamped by an Apex 35 stem, the grips and saddle come from Ergon. The handlebar has a rise of 40mm, as the steerer of their secondhand fork was a bit on the short side.
The bike was designed with a certain trail in mind. It's rooty and very fast, and their trail bikes were just not capable enough. The goal of the whole project was to get a nicely performing bike with sturdy parts. They intentionally didn't use any carbon parts. Because they bought a lot of used parts, the whole bike wasn't too expensive in terms of money - however Michi and Pascal acknowledge that they've invested a ton of time into this project.
When your handlebar diameter is nearly the same as the top tube diameter, you know you're riding a steel frame.
BikeYoke dropper post and the brazed-on Scar Cycles head badge.
How do they like the bike? 11 out of 10. They say that the bike performs perfectly on the trail that they had in mind when designing the bike. The steel frame has some flex which took some time to get used to, but it provides a lot of grip in turns and off-camber sections. Nevertheless, they think they'd have even more fun on a shorter bike and in case they ever build a second frame, they'd do some little things differently.
Michi and Pascal designed two versions of the rocker. The one you see in the photos was designed using generative design and weighs 150 g. The second
one was also additively manufactured and optimized to the max, so that they could achieve a weight of 130 g. When designing the generative design version, estimating the loads was difficult, so this version turned out a bit heavier. Further, they did some design-assisted FEM analysis. Again, it was difficult for them to make suitable load assumptions.
All 3D printed steel parts are hollow and have a wall thickness of about 1mm. The bearing seats in the dropouts are printed directly, without any rework.
The rear end got some extra reinforcements compared to the original aluminum Kavenz.
Pirope A.30 wheels keep the weight low.
Michelin Wild Enduro front and rear tires.
"Heavy but awesome" Michelin tires.
Michi and Pascal are grateful for the support they got from ECOPARTS
, who not only gave them modeling tips but also provided test material for soldering. They would also like to thank Stefan from Scar Cycles
for his support and brazing the frame. They built a very good relationship and exchange ideas on a regular basis.