Definitions

soft ground

Ground pressure

Ground pressure is the pressure exerted on the ground by the tires or tracks of a motorized vehicle, and is one measure of its potential mobility, especially over soft ground. Ground pressure can be measured in (for example) pounds per square inch (PSI) or kilopascals (kPa). Ground pressure can be calculated with the formula (loaded weight divided by ground contact area) The ground pressure of motorized vehicles is often compared to the ground pressure of a human foot, which can be 9 - 12 PSI while walking or as much as 1,920 PSI for a person in spike heels.

Increasing the size of the contact area on the ground (the footprint) in relation to the weight decreases the ground pressure. Ground pressure of 2 PSI or less is recommended for fragile ecosystems like marshes. Decreasing the ground pressure increases the flotation, allowing easier passage of the body over soft terrain. This is often observed in activities like snowshoeing.

Example Ground Pressures

All example are approximate, and will vary based on conditions

Human on Snowshoes: 0.5 psi

Rubber-tracked ATV: 0.75 psi

Diedrich D-50 - T2 Drilling rig: 3.8 psi

Human Male (1.8 metre tall, medium build): 8 psi

M1 Abrams tank: 15 psi

1993 Toyota 4Runner / Hilux Surf: 25 psi

Adult horse (1250 lb): 25 psi

Passenger car: 30 psi

Wheeled ATV: 35 psi

Mountain bicycle: 40 psi

Racing bicycle: 90 psi

Note pressures for Man and Horse are for standing still. A walking human will exert double it's standing pressure. A galloping horse will exert up to 500 psi

Related Reading

  • Theory of Ground Vehicles

References

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