4 ms·

It isn't just pressure, total weight matters too. 1000 psi is WAY too high. Keeping ground pressure as low as 10 psi is generally the recommendation for heavy

It isn't just pressure, total weight matters too. 1000 psi is WAY too high. Keeping ground pressure as low as 10 psi is generally the recommendation for heavy equipment, but a person walking might get up as high as 20 psi and doesn't cause compaction on soil with a reasonable organic matter content (5% or more I think?). Here's a good explanation: https://extension.psu.edu/avoiding-soil-compaction https://extension.psu.edu/avoiding-soil-compaction

thatcat 8y ago
Hm, my mistake, thanks for the link. Total weight is related to pressure through the formula: P = F/A. Weight is F.
- deialtrous 8y ago
  Not when you are using pneumatic tires. That gives you the pressure applied to the air in the tire, not to the ground. The tire pressure determines ground pressure.
  - thatcat 8y ago
    Lowering tire pressure widens the base of the tire, changing the contact area(A) and adds some shock absorbing. The fundamental equation still applies to static conditions. Figure 3 on page 279 explains it. https://www.researchgate.net/publication/224830979_Ecoefficient_Timber_Forwarding_on_Lowland_Soft_Soils https://www.researchgate.net/publication/224830979_Ecoeffici... The reason I thought 1000 psi was low is explained on 278, the ground bearing capacity columns minimum value is 20 mpa or 2900 psi. The numbers in your link are dynamic pressures at depths of 14 / 28 inches. The area where the force is applied increases as the stress is distributed in the soil. The 2900 is a surface value.
    - deialtrous 8y ago
      No. Air is a fluid. Like all fluids, it exerts pressure equally in all directions. A pneumatic tire is not simply a shock absorber, nor does it need to deform for its internal pressure to change the ground pressure. It is transferring force to the entire tire that would be transferred to the ground if you used a solid wheel to contact the ground. You are applying X pounds of force to Y volume of air, which is distributing that force across the entire internal surface area of the tire. It is not the contact area of the tire to the ground that has force exerted on it, it is the surface area of the interior of the tire. This is not hypothetical, measure the ground pressure, change the tire pressure and measure again. It is trivial to verify for yourself.
      - thatcat 8y ago
        Thank you very much for the explanation. I'm not really familiar with the empirical methodology or equipment required to measure pressure between two surfaces.

thatcat 8y ago

Hm, my mistake, thanks for the link. Total weight is related to pressure through the formula: P = F/A. Weight is F.

deialtrous 8y ago
Not when you are using pneumatic tires. That gives you the pressure applied to the air in the tire, not to the ground. The tire pressure determines ground pressure.
- thatcat 8y ago
  Lowering tire pressure widens the base of the tire, changing the contact area(A) and adds some shock absorbing. The fundamental equation still applies to static conditions. Figure 3 on page 279 explains it. https://www.researchgate.net/publication/224830979_Ecoefficient_Timber_Forwarding_on_Lowland_Soft_Soils https://www.researchgate.net/publication/224830979_Ecoeffici... The reason I thought 1000 psi was low is explained on 278, the ground bearing capacity columns minimum value is 20 mpa or 2900 psi. The numbers in your link are dynamic pressures at depths of 14 / 28 inches. The area where the force is applied increases as the stress is distributed in the soil. The 2900 is a surface value.
  - deialtrous 8y ago
    No. Air is a fluid. Like all fluids, it exerts pressure equally in all directions. A pneumatic tire is not simply a shock absorber, nor does it need to deform for its internal pressure to change the ground pressure. It is transferring force to the entire tire that would be transferred to the ground if you used a solid wheel to contact the ground. You are applying X pounds of force to Y volume of air, which is distributing that force across the entire internal surface area of the tire. It is not the contact area of the tire to the ground that has force exerted on it, it is the surface area of the interior of the tire. This is not hypothetical, measure the ground pressure, change the tire pressure and measure again. It is trivial to verify for yourself.
    - thatcat 8y ago
      Thank you very much for the explanation. I'm not really familiar with the empirical methodology or equipment required to measure pressure between two surfaces.