  We present an improved method for predicting the Sunyaev-Zeldovich (SZ)
effect in galaxy clusters from spatially-resolved, spectroscopic X-ray data.
Using the deprojected electron density and temperature profiles measured within
a fraction of the virial radius, and assuming a Navarro, Frenk & White (1995)
mass model, we show how the pressure profile of the X-ray gas can be
extrapolated to large radii, allowing the Comptonization parameter profile for
the cluster to be predicted precisely. We apply our method to Chandra
observations of three X-ray luminous, dynamically relaxed clusters with
published SZ data: RX J1347.5-1145, Abell 1835 and Abell 478. Combining the
predicted and observed SZ signals, we determine improved estimates for the
Hubble constant from each cluster and obtain a weighted mean of
H_0=69\pm8km/s/Mpc for a cosmology with Omega_m=0.3 and Omega_Lambda=0.7. This
result is in good agreement with independent findings from the Hubble Key
Project and the combination of cosmic microwave background and galaxy cluster
data.
