  (Shortened version): The mass loss rates, expansion velocities and
dust-to-gas density ratios from millimetric observations of 119 carbon-rich
giants are compared, as functions of stellar parameters, to the predictions of
recent hydrodynamical models. Distances and luminosities previously estimated
from HIPPARCOS data, masses from pulsations and C/O abundance ratios from
spectroscopy, and effective temperatures from a new homogeneous scale, are
used. Predicted and observed mass loss rates agree fairly well, as functions of
effective temperature.(shortened). Four stars with detached shells, i.e.
episodic strong mass loss, and five cool infrared carbon-rich stars with
optically-thick dust shells, have mass loss rates much larger than predicted
values.(shortened). Recent drift models can contribute to minimize the
discrepancy since they include more dust. Simple approximate formulae are
proposed.
