In reality, this idealized situation may be different
both in size and direction. The actual wheel speed is
denoted by v. The longitudinal slip/skid of a wheel is
described as the difference between wheel speed vx and
tractor’s speed v. From this difference we can calculate
slip/skid coefficient d by using the formula below. It is
expressed as the ratio between the decrease in the actual
speed and the theoretical speed; this expression is given
by