In the flurry of beautiful and interesting bikes that popped up at the Philly Bike Expo, we caught sight of this steel high pivot machine and had to know more. At his workshop in the small town of Pine, Colorado, Zach Geller cooked up this 160mm 29er to be his personal trail bike. The build is certainly eye-catching, and the undertaking is no small feat, so I sat down with Zach to get the story on the development of this bike, and on Acoustic Cycles in general.
How long have you been building?
I started building in 2019, and have transitioned to building full time as of this year. Taking a weeklong framebuilding course with Brew Bikes in Boone, NC kickstarted the new venture.
Why custom over stock, especially in the high-performance mountain bike space?
I had always worked in bike shops, and was consistently on the yearly cycle of buying and flipping the newest bikes on the market, but over time just got sick of keeping up with the updates. I wanted to make something that would fit me and my uses, while also lasting a long time. I've been riding one of my first hardtail frames for four years now, and it still works just as well as day one. The beauty of a custom frame is the small geo tweaks you can make, as opposed to being locked into stock sizing.
As someone always iterating on geometry and design, does it feel like mtb geo has reached a point of balance?
I’d like to say we’ve hit a plateau, but someone always comes out with something you want to try. Within the past couple years, we’ve come to numbers that work pretty well for descending and climbing. Reach is a strong preference for people, so that’s why I stuck with front end being customizable.
The numbers are pretty bang-on for a modern enduro bike.
Why go high pivot for your first full suspension? How did the design and build process go?
It might sound cliche, but I ride up for the downs, so I wanted to make the best descending trail bike I could. I've always ridden 4-bar bikes, and preferred that to the single pivot alternative, so it was worth the extra complication for me.
I design in Fusion360, BikeCAD, and Linkage, and was able to get a pretty firm idea of how the suspension would perform based on that data. I actually pulled a lot of info from the Pinkbike Behind the Numbers
articles, which helped me optimize relative to other bikes out there.
Idler placement was a tricky one to determine, so I built a test jig that allows me to slightly change the location and size (currently 17t) of the idler to optimize things. It's been snowing since I returned from the Philly Bike Expo, so I haven't had a real chance to ride the bike yet.
One last note on the build process - I ended up 3D printing a plastic model of the entire rear end of the bike, in order to test fitment and clearances before I pulled the trigger on a metal assembly. This was a huge help in dialing in the design without having to iterate too much.
High performance purple.
How would you describe your flavor of frame building?
From a 10,000’ view, the majority of builders are road-oriented, where Acoustic is very focused on mountain bikes. I care a lot about form and function working together, so that every bend is intentional and the lines flow well. In the end the bikes have to ride well too, I want these things to last.
Do you have any primary influences when it comes to bike design and fabrication?
Community-wide, there's just so much information and help. Chris at 44bikes is on his fourth iteration of his full suspension design, so he's been a great resource. Adam Prosise machined the rockers for the bike and was a good sounding board for the manufacturing and suspension performance. Sean Handerhan made the dropouts, clevis, and main pivot. The clevis required 5th axis machine, so he was key to getting this thing made. Walt Wehner of Waltworks has a trove of information on his blog, which always proves helpful.
Do you think there are lessons larger manufacturers could learn from solo fabricators like yourself?
Smaller builders can pivot much quicker and try things sooner. Prototyping is quick and immediate, which is great for testing out ideas and fit. We're seeing more desire for geometry tweaks and customization in mountain bikes, but ultimately it can't match what you can get with a custom builder.
The supply chain is much more immediate, which is just nice from an availability standpoint.
Are there any bikes out there you’d love to ride? New or old, what intrigues you?
Evan Turpen's Contra
bike, and the Forbidden Druid
. I want to talk to Evan about his design process, and what all changed between prototype and final product. The Forbidden design seems to take a different approach to the high pivot design, and I really like how transparent they are with information on their website.
Are there plans to scale this design, maybe even offer a stock frame?
My current pipe dream is to have a stock of rear end assemblies ready to go, and be able to weld up custom front triangles for each customer. I'm currently in talks with a metal 3D printing shop about getting pivots and dropouts made, in order to shave weight and to help make fabrication easier and quicker.
Not that it matters, but how much does it weigh?
Current build weight is about 40 pounds, maybe closer to 41 now as I just installed a coil conversion on the fork.
Contact Zach and see more at the Acoustic Cycles website
All photos by Alexandra Demopoulos.