  Recently, it has been shown that a correlation exists between the rate of
shear and the spiral arm pitch angle in disk galaxies. The rate of shear
depends upon the shape of the rotation curve, which is dependent upon the mass
distribution in spiral galaxies. Here, we present an imporoved correlation
between shear rate and spiral arm pitch angle, by increasing the sample size.
We also use an adiabatic infall code to show that the rate of shear is most
strongly correlated with the central mass concentration, c_m. The spin
parameter, $\lambda$, and the fraction of baryons that cool, F, cause scatter
in this correlation. Limiting this scatter, such that it is equal to that in
the correlation between shear rate and pitch angle, and using a value of F=0.1
to 0.2, the spin parameter must be in the range 0.03<lambda<0.09 for spiral
galaxies. We also derive an equation which links spiral arm pitch angle
directly to c_m.
