  Rapidly rotating neutron stars can be unstable to the
gravitational-wave-driven CFS mechanism if they have a neutral point in the
spectrum of nonaxisymmetric f-modes. We investigate the frequencies of these
modes in two sequences of uniformly rotating polytropes using nonlinear
simulations in full general relativity, determine the approximate locations of
the neutral points, and derive limits on the observable frequency band
available to the instability in these sequences. We find that general
relativity enhances the detectability of a CFS-unstable neutron star
substantially, both by widening the instability window and enlarging the band
into the optimal range for interferometric detectors like LIGO, VIRGO, and
GEO-600.
