Vehicle mass directly determines viability on compressible substrates. Bearing pressure — mass divided by contact footprint area — limits traverse on soft surfaces where substrate compression creates impassable conditions or platform immobilization.
Substrate-Bearing Relationship
| Vehicle Mass Class |
Typical Mass Range |
Bearing Pressure (kg/cm²) |
Optimal Substrates |
Marginal Substrates |
Prohibited Substrates |
| Ultra-light |
<500 kg |
0.08–0.12 |
Peaty, wet sand, silt, fine silt |
Clay (wet), decomposed rock |
None (within normal environments) |
| Light |
500–1,000 kg |
0.12–0.25 |
Sand, gravel, sand/silt mix, hard-packed clay |
Peaty substrate, clay (wet) |
Saturated silt, deep peat |
| Medium |
1,000–1,800 kg |
0.25–0.45 |
Gravel, hard-packed clay, sand with stone |
Sand, silt, clay (damp) |
Saturated clay, peaty substrate, deep sand |
| Heavy |
1,800–3,000 kg |
0.45–0.75 |
Stone, bedrock, gravel (well-compacted) |
Hard clay, sand/gravel composite |
Saturated soils, peat, fine sand, deformable substrates |
| Very Heavy |
>3,000 kg |
>0.75 |
Bedrock, engineered surfaces |
Stone, gravel (must be large-grain) |
Most natural substrates; primary/secondary routes only |
Implications for Route Selection
Light platforms (<1,000 kg) access tertiary routes and soft substrates where heavier platforms immobilize. Ultra-light platforms (<500 kg) traverse saturated peaty terrain and deep silt impassable to standard platforms. Conversely, heavy platforms restrict themselves to prepared routes and engineered substrates. Route 6 (Boulder Field) and Route 3 canyon sections provide case studies: platforms <800 kg achieve full clearance efficiency; platforms >2,000 kg require alternate corridors or staged operations.
See Surface Classification Reference for substrate descriptions and bearing-capacity tables by region.