GUIDELINES FOR SNOWMOBILE TRAIL
           GROOMER OPERATOR TRAINING


A Resource Guide for Trail Grooming Managers and Equipment Operators:


Chapter 2 - Grooming Equipment
      .
Important Characteristics of Grooming Tractors:

There are several characteristics that are important to understanding the capabilities and the proper operation of grooming tractors. These characteristics include:

Ground Pressure:
A vehicle that is designed to work in snow must stay on or near the surface rather than sink in and plow through the snow. This is accomplished by spreading the weight of the vehicle out over the tracks, much as a snowshoer’s weight is distributed by the snowshoes.

The technical measure of the vehicle’s ability to distribute weight is called ground pressure. Ground pressure is calculated by dividing the overall weight of the vehicle by the total area of the track which remains in constant contact with the snow and is most often expressed in pounds per square inch (psi) or kilogram-force per square centimeter (ksc).

Typical ground pressures for moderate-light to heavy grooming tractors range from 0.8 psi (0.056 ksc) to 1.2 psi (0.084 ksc). It is very important that tractor ground pressure not exceed these limits.

If ground pressure is too high, the vehicle will sink into snow rather than stay on top. If ground pressure is too low, the unit may not have sufficient traction to pull a drag up hills or through deep, heavy snow.

Overall Weight:
Within reasonable limits, the overall weight of the tractor can be compensated for by matching it with the appropriate track area. However, overall weight is a factor in terms of existing bridge loading limits and crossing frozen bodies of water.

Because grooming vehicles are typically very heavy, it is recommended that they never be operated on frozen bodies of water without special planning, testing, and training since doing so could lead to equipment damage, serious personal injury, or death.

Engine Horsepower and Torque:
Regardless of whether a diesel or gasoline engine is installed in a particular tractor, the key measurements of its capability are its horsepower and torque. Always use the same measurements when comparing horsepower, since there are gross, net, and power-take- off (PTO) measurements.

Gross brake horsepower is a good basic unit for comparing the relative power of engines.
Engine torque is an overlooked rating that is very important for all grooming tractors. Torque relates to the ability of the tractor to get a heavy drag moving.

The high static loads of modern multi-blade drags require a high degree of engine torque to get a drag moving from a dead stop.

Center of Gravity:
A vehicle’s center of gravity is a point around which its weight is evenly balanced. Figure 2.1 is an example of the center of gravity for a typical 2-track grooming tractor.

                  
Figure 2.1 Center of gravity for a typical 2-track grooming tractor

A vehicle’s center of gravity is significant any time it must operate on a non-level surface such as when climbing or descending steep grades or when side hilling. In terms of stability, the lower to the ground the unit’s center of gravity is the more stable it will be on non-level surfaces. Operators should keep this factor in mind to avoid getting into unsafe situations.

Tractive Effort and Coefficient of Friction:
Tractive effort is defined as the amount of torque that can be applied to a track before the track looses traction and spins without moving the vehicle forward.

The coefficient of friction between the track and the ground or snow is the limiting factor of when the tracks will loose traction. Coefficient of friction is determined by the overall vehicle weight, the amount of track on the ground, the cross-link design of the track, and the weight distribution along the length of track that is in contact with the surface.

The ideal weight distribution on the tracks is having the balance point, from front to rear of the vehicle, at or near the center point of the length of track, as shown in Figure 2.1 above.

When a track breaks traction it is actually shearing the snow through the force that the cross-links are placing on it. Fresh, unpacked snow shears much more readily than hard packed snow.

When a vehicle breaks traction, spins out, and gets stuck, it happens because the force required to shear the snow is less than the force required to pull the load. The load is made up of both the drag and the tractor.




  Next Section - Snowmobiles and ATVs as
                          Grooming Tractors

Support Us By Supporting Our Sponsors.
Please Let Our Sponsors Know You Found Them On AbsoluteSnowmobile