Traction Efficiency vs. Pressure Gradient Correlation Database (12 Soil Types)

Traction efficiency—the ratio of usable tractive force to applied wheel load—is critically dependent on how pressure is distributed beneath a rolling tire, particularly its vertical gradient (rate of change of normal stress with depth). Steep gradients (high dP/dz) often indicate localized stress concentration near the surface, leading to excessive sinkage and reduced efficiency; shallow gradients suggest deeper stress penetration and better load support—especially in cohesive or high-density soils. This database synthesizes field and laboratory measurements (e.g., pressure-sensitive films, embedded transducers, controlled-traffic tractor tests) across 12 representative soil types—from loose sand and loamy sand to clay loam and heavy clay—each characterized by USDA texture class, moisture content range (θ = 0.10–0.35 m³/m³), and corresponding Mohr–Coulomb parameters. Each soil entry includes regression-derived correlation curves (log–log or power-law fits) linking normalized traction efficiency (η_trac) to dimensionless pressure gradient (dP/dz normalized by soil strength parameter, e.g., c + σ₀ tanφ). The Excel structure supports parametric sensitivity analysis: users input tire radius, width, inflation pressure, and slip ratio to interpolate or extrapolate η_trac using soil-specific lookup tables and piecewise interpolation functions. Applications span precision agriculture (optimizing tire selection to minimize compaction while maximizing draft efficiency), autonomous off-road navigation (real-time traction prediction for path planning), and ISO-standardized testing protocols for agricultural tires (e.g., ISO 5263-2).