We have measured the in-plane magnetoresistance (MR) of a series of submicron single domain Permalloy wires to study two important magnetization reversal modes, coherent rotation and curling. With the consideration of both micromagnetic configurations, the MR curve can be decomposed in a reversibly bell-shaped curve and an irreversibly V-shaped discontinuity in low field, respectively. The discontinuity jump occurs at a switching field characterizing the curling mode. The angular dependence of the switching field is well described by the theoretical prediction of Aharoni model under the consideration of the whole volume curling. Moreover, we found that the low angle switching field decreases with increasing wire width (decreasing the aspect ratio) as 1/width, consistent with the curling model for a long slender ellipsoid.