where rd is a dynamic radius of the wheel (distance from the
axis to the line of contact between tire and soil, where
thrust force is generated).
When 4WD tractor works with front-mounted loader,
deformations of its front and rear tires do not correspond
to the specified proportions. As a result, we have different
theoretical wheel speeds. When theoretical speeds are different,
the actual front and rear wheel speeds may be equal,
but one pair of driving wheels may slip, and the other –
skid. We can record the following equation for inter-relation
between speeds: