Design and Engineering: The G-Bike
The G-Bike frame was designed around a number of features and requirements. It was designed to utilize a single pivot and zero chain growth design, be strong enough to endure extreme riding forces, maintain a medium leverage ratio through the length of its travel, have a linearly increasing shock rate, and have a shock that is easy to remove/replace during tuning and maintenance. The single high pivot design was chosen for its ability to maintain high speed stability, reduce chatter, and stay consistent over a variety of terrain, which makes it a very useful all around design. Additionally, this single pivot between the triangles is the perfect location to centralize the mass of the Alfine hub. A big thanks to Zerode, Cane Creek, and Race Face for their assitance on meeting industry standards across the project.
All Photographs and Drawings by Alex Pfiffner
As-designed Solidworks model
Test Ride by Alex Pfiffner
As-built assemblies
One of the essential processes of this design was to replace the typical external drivetrain with an internal, integrated gearbox (the Shimano Alfine 8). In order to counteract the limitations of a typical single chain design, the G-Bike was designed as a two-chain system. The gearbox is coupled to the drive train with a custom sprocket (design courtesy of Zerode Bikes) and the existing Alfine sprocket. The gearbox is located at the pivot directly under the rider to keep the center of mass as low as possible, thus increasing the stability of the bike during use. The integration is possible by first placing the hub, then designing the suspension linkage around the extra wide frame.
One of the biggest overall challenges was to properly design a linkage system within the ambitious project objectives. It not only needs to meet these objectives, but also be customizable and expandable for different suspension ratios and shock rates in future iterations of the prototype. This would allow the bike to satisfy many riding styles on many terrains, and switch between the linkage set-ups by choice, which is often desired by performance athletes. Due to industry standards and size constraints, the linkage system was placed higher on the bike, leaving room for the gearbox and shock below. This unique layout is just as applicable to non-gearbox downhill frames as well.
