The effect of runout on the variation in friction and wear failures that occur during the sliding of magnetic recording heads against carbon-coated, thin-film disks was investigated. The shape of disk runout was modified by sandwiching metallic shims between the disk and the hub of a test spindle as well as by varying the torque on the clamping screws. These procedures smoothed the complicated runout curve to a simple sinusoid-like curve, and at the same time increased the peak-to-trough runout. Drag tests were conducted on delubricated disks until failure occurred. The test results have shown that smoothing the runout curve to a simple sinusoidal shape increases the time to failure by a factor of ten, provided that the peak-to-trough runout stays roughly below 65 μm. Smoothing the runout curve does not prolong the time to failure when the peak-to-trough runout is larger than about 70 μm. Elementary dynamical analysis of the head further suggests that small wavelength runouts induce head oscillation and early disk failure.Presented at the 46th Annual Meeting in Montreal, Quebec, Canada April 29–May 2, 1991