  It is well-entrenched folklore that torsion gravity theories predict
observationally negligible torsion in the solar system, since torsion (if it
exists) couples only to the intrinsic spin of elementary particles, not to
rotational angular momentum. We argue that this assumption has a logical
loophole which can and should be tested experimentally. In the spirit of
action=reaction, if a rotating mass like a planet can generate torsion, then a
gyroscope should also feel torsion. Using symmetry arguments, we show that to
lowest order, the torsion field around a uniformly rotating spherical mass is
determined by seven dimensionless parameters. These parameters effectively
generalize the PPN formalism and provide a concrete framework for further
testing GR. We construct a parametrized Lagrangian that includes both standard
torsion-free GR and Hayashi- Shirafuji maximal torsion gravity as special
cases. We demonstrate that classic solar system tests rule out the latter and
constrain two observable parameters. We show that Gravity Probe B (GPB) is an
ideal experiment for further constraining torsion theories, and work out the
most general torsion-induced precession of its gyroscope in terms of our
torsion parameters
