In November 2022 I finished converting an existing bike frame to a frontloader cargo bike. To the best of my knowledge, this was the first bike frame (or sub-frame, I’ll call it that from now on) in the world built using forged carbon lugs.
The new sub-frame connects to the existing downtube and front dropout. The front wheel is pushed forward by 1,200mm and replaced with a 24″ wheel. A pair of aluminium RHS rubes (50x25mm at 3mm wall thickness) form the backbone of the sub-frame. The existing forks are connected to a new headset on the sub-frame, whereby the steering steering is transmitted to the new front wheel using a cable system (2 x 1.6mm cables per side).
All of the lugs were custom built from forged carbon fibre using 3D printed moulds. This project represented a long process of trial and error in developing a method to design and build lugs for bike construction. From this I learnt a lot about how to design parts to be easily built and de-moulded, how to print and prepare moulds to improve their ‘survivability’ and the part’s surface finish (before finishing), and how to design geometry to best suit the material properties.
What’s more, this project gave me the opportunity to play with geometry affecting a frontloader cargo bike, such as wheelbase, fork trail and wheel flop, load distribution etc., which I’m sure will be valuable when it comes time to design a new frontloader model!
