How Big Must a Wheelbarrow Wheel Be? A Bekker Sinkage Bound for a 100 kg Load on Sand and Soft Clay

A wheelbarrow that is easy to push on a hard yard can become nearly unusable on sand or soft clay, and the difference is set mostly by the wheel. This paper uses a Bekker-type pressure–sinkage and compaction-resistance model to compute the push force for a 100 kg payload (115 kg gross, 846.1 N carried by the wheel) across wheel diameters of 0.25–0.60 m and widths of 0.05 m and 0.10 m, on dry sand and on soft (saturated) clay with stated soil parameters. Against a stated sustained human push limit of 150 N, the minimum diameter is 0.40 m for a wide wheel on soft clay and 0.57 m for a narrow wheel on soft clay. On dry sand no diameter in the studied range is sufficient: the wide wheel still requires 201.8 N at 0.60 m, and the model must be extrapolated to 0.94 m (wide) and 1.31 m (narrow) to reach 150 N — diameters no practical wheelbarrow can carry. The verdict on the common small wheel of about 0.30 m is direct: at 0.30 m the required push is 394.3 N on sand with a narrow wheel, 318.1 N on sand with a wide wheel, 243.4 N on soft clay with a narrow wheel, and 185.4 N on soft clay with a wide wheel — between 1.24 and 2.63 times the sustained limit in every case. The practical wheel sized by this study is 0.60 m in diameter and 0.10 m wide: it works on soft clay, with margin, and it still does not make a fully loaded barrow pushable on loose dry sand, where the load, not the wheel, must change.