T-Mar

Let me clarify that, according to Brandt, the root cause is not "lack of lubricant" but "lubricant failure". When the bicycle is ridden in a straight line, the ball bearings experience microscopic vibrations called fretting, which results in dispersal of the lubrication film and metal to metal contact between the balls and race. The balls weld to the race and any subsequent rotation of the headset tears the softer material from the race and replenishes the lubrication film on the ball bearings.