The effects of coulomb collisions on solar wind ion velocity distributions are investigated by using Helios data obtained between 0.3 and 1 AU. The mean free path of ions moving at thermal speed (in the solar wind frame) varies by three orders of magnitude in dependence on the plasma parameters. The number of collisions (roughly defined as collision frequency times the solar wind expansion time) can easily exceed one in low-speed wind near the heliospheric current sheet. In these regions, almost Maxwellian distributions are observed. In solar wind with intermediate speeds (ranging from 400--600 km/s) one usually finds distributions with a nearly isotropic core which again can be understood by the action of coulomb collisions. On the other hand, the major part of high-speed solar wind ion distributions can by good reason, be called collisionless on local scales.