This master thesis was completed at the TU Delft in collaboration with Pezy Group for the company O4 Wheelchairs, with the goal of optimising the production and assembly of their wheelchairs, by standardising the wheelchair design.  In the field of fully customisable wheelchairs (ultra-personalised products), the conflicting interest of the need for customisability and standardisation to optimise production is prevalent. By standardisation of the wheelchair assembly, without compromising the needed customisability, the production time of O4 wheelchairs can be improved benefiting both the company and its stakeholders. To achieve the goal of a shorter production time, the production at O4 Wheelchairs was analysed, and multiple opportunities were formulated. These opportunities were further elaborated by turning them into design questions, and their potential was assessed with brainstorming sessions and low-fidelity prototyping. From these opportunities, one direction for a concept was chosen to be fully developed in this project. In contrast, the others were formulated into a roadmap of specific steps for O4 to take to improve their production. The chosen concept was further developed by prototyping and testing, ranging from cardboard and 3D printed models to fully laser-cut aluminium parts. This led to a design proposal for a new fender assembly. This new fender assembly integrates the brake into the assembly and ensures exact fixation without the need for measuring. It is usable in all wheelchair configurations and with the three sold wheel sizes.Testing the new fender assembly with assembly workers at O4 Wheelchairs resulted in an estimated time of 16 minutes, compared to the 37 minutes it takes to assemble the old fender assembly. The improvement of 44% in time, a cost decrease of roughly €30 and the design being less error-sensitive due to the straightforward way of fixation, all add to the value brought to O4, with the design proposal.This project provides multiple starting points for O4 Wheelchairs to further improve their production and product line. The design proposal also promises a substantial improvement to their current fender assembly.