Tire rating based on soil compaction capacity

•CC numerical index of off-road tires evaluates their compaction effect on standard soil.•CC index takes into account the increase of soil dry density at the depth 20–50 cm.•CC index is applicable to tires with at least 70 kPa mean contact pressure on firm ground.•Related LCC index serves to compare soil friendliness of tires with less than 70 kPa m.c.p.•CC/LCC rating may adjoin all inflation pressure – load data in tire technical catalogs.

Compaction Capacity (CC) rating of tires presents a unique numerical CC index evaluating soil compaction risk of loaded tires. The CC rating presented here is a final product of experimental research and analysis of relations between external load and soil compaction, avoiding the intermediary role of soil stress. The research included laboratory model measurements of soil compaction by rigid round pressure plates in a cylindrical soil container. Equation for the CC index reads: CC = 1000 [(soil dry density/1420) − 1], where the number 1420 indicates the dry density of loam in kg/m3, critical for plant growth. The CC rating takes into account the area of tire−ground contact patch and tire load, which depends on inflation pressure. If the average dry density is 10% higher than the critical dry density, the CC index equals 100. This is considered as a practical limit to ecological tire operation on cultivated crop-producing land. Agricultural tires with mean contact pressures less than 70 kPa have zero CC index. Their qualities are classified by Low Compaction Capacity (LCC) index based on 1290 kg/m3 soil dry density. Both the CC and LCC indices do not distinguish between towed and driven wheels. The tables in this paper show how these simple indices can complement load data published by tire manufacturers.