A closed form for the velocity difference between impurity ions and the main ions in neoclassical theory has been obtained in terms of the pressure and temperature differences. This difference has important diagnostic implications since typically the impurity velocities are measured and the main ion rotation inferred from this. Although the individual velocities cannot be analytically evaluated to the required order in inverse aspect ratio, the difference in a two ion species plasma can be calculated using an approach similar to the one used for bootstrap current. The formula has also been simplified to the case of trace impurity ions, which then is applicable to any number of trace impurities. The resulting difference between two different trace impurity ions in an otherwise pure plasma can be checked against experiments.