The first principle is to produce a wider tire to increase the contact
area between the tire and surface. The larger contact area
distributes the load over a relatively broad area, reducing the ground
pressure as compared to conventional tires. (Think an 800 pounds man
using pogo sticks as feet versus sheets of plywood).
The second principle is to have a low air pressure tire allowing the
tires to form over and around obstacles, rather than moving them out
of the tire's way. In soft soil, the ratio between the pressure of
the tire and the pressure the soil can support determines the amount
of soil disturbance. (Think rolling an under-inflated balloon over an
irregular surface versus a bowling ball)
The third is to have a shallow tread pattern with a dense pattern of
lugs. The denser the pattern and shallower the tread, the more
surface area and less ground disturbance in the soil. This comes at a
price however, the less aggressive the pattern, the less traction you
get, especially in non-ideal conditions.
You may notice on many carts that they use different tires for the
front than the back. Most carts are driven by the rear wheels, using
the front tires to only to steer. Since these tires mostly need
vertical traction and little horizontal traction, they are often using
a very passive pattern that is ribbed vertically with very narrow
horizontal gaps. This style provides the least amount of ground
disturbance, but is not suitable for the rear tires of the cart. Most
rear tires use a saw tooth tread design rather than open lugs, giving
it ample traction while still keeping the most amount of contact area.
In the end, the tires still do damage the soil, but the goal is to
minimize the impact by using tires that are designed around the above
principles. |
