Sole Cost per Kilometre: A Cost-per-Distance Ranking of Sole Materials a Low-Income Wearer Can Obtain

For a wearer who walks several kilometres every day, the price of a pair of soles is the wrong number to compare: what matters is the cost per kilometre walked before the sole wears out. This paper ranks six sole materials that a low-income wearer can actually obtain — cut tyre rubber, vegetable-tanned soling leather, hardwood, woven coir or rope, recycled plastic (HDPE) sheet, and layered cloth-and-resin — by modelling wear as a linear loss of thickness from stated starting thicknesses to stated wear-out thicknesses at stated wear rates, with stated local prices per pair. Cut tyre rubber is the cheapest sole per distance by a wide margin: it lasts 11,666.7 km and costs 0.1029 US dollars per 1,000 km, about one seventeenth of the cost per 1,000 km of leather (1,666.7 km life, 1.80 dollars per 1,000 km). Hardwood is second at 0.16 dollars per 1,000 km over a 5,000.0 km life. The cheapest purchase, layered cloth-and-resin at 0.30 dollars a pair, is a false economy beyond a short horizon: its cumulative cost first exceeds the cumulative cost of a tyre-rubber pair at 6,401 km, and covering 10,000 km in cloth-and-resin soles costs 2.10 dollars in seven pairs against 1.20 dollars for a single pair of tyre rubber. The ranking is unchanged when all wear rates are raised by 50 percent. The practical rule the model supports is simple: judged per kilometre rather than per pair, durable scavenged rubber beats every cheaper-to-buy alternative once the wearer walks more than a few thousand kilometres a year.