We investigate the correlations among stellar mass (M*), disk scale length (R_d_), and rotation velocity at 2.2 disk scale lengths (V_2.2_) for a sample of 81 disk-dominated galaxies (disk/total>=0.9) selected from the SDSS. We measure V_2.2_ from long-slit H{alpha} rotation curves and infer M* from galaxy i-band luminosities (L_i_) and g-r colors.