Design and stiffness assessment of non-pneumatic bicycle tyres with latticed cores produced by fused filament fabrication

Conventional tyres often suffer from issues such as air pressure maintenance and blowouts. Recently, companies have begun developing non-pneumatic tyres (NPTs) made from rubber-like materials, offering potential benefits such as reduced environmental impact. However, research on this technology remains relatively underexplored. This study investigates the design, and mechanical performance of NPTs produced via fused filament fabrication (FFF) using thermoplastic polyurethane. The NPTs were developed through iterative design stages, combining experimental testing and numerical analysis for evaluation. Two base lattice configurations were employed: a hexagonal honeycomb and a hollow spherical-based structure. Initially, relative density was kept constant while cell size was varied to assess its effect on vertical stiffness and energy absorption. Based on the results, one design from each lattice type was refined, focusing on shear layer geometry and cell wall thickness. Compression tests evaluated vertical stiffness and energy absorption, while numerical simulations also analysed lateral and longitudinal stiffness to simulate cornering and braking scenarios. The numerical simulations are performed using a nine-parameter Mooney-Rivlin hyperelastic material model calibrated from experimental stress-strain data. Results indicated that hexagonal designs exhibited higher vertical and lateral stiffness, while spherical designs demonstrated superior longitudinal stiffness. Design adjustments yielded NPTs with vertical stiffness closely aligning with standard commuter bicycle tyres. Deformation behaviour revealed a combination of bending and elastic buckling in cell walls, with numerical simulations capturing key trends despite underestimating stiffness. This study demonstrates the feasibility of functionally optimized NPTs via FFF, offering a promising alternative for bicycle tyres.