Oct 172011
Headsets on tall bikes generally wear much longer than headsets on small bikes, even though the users of the tall bikes are heavier. This is because any small angular discrepancy of the orientation of one bearing relative to the other is magnified with a short head tube, while a long head tube reduces the effect.
Imagine a stress on the fork deflecting a bearing; with a short head tube, the angular discrepancy between the two bearings is greater than when that same deflection is extrapolated over a large distance between the bearings. In other words, long head tubes keep the bearings closer to parallel under use better than do short head tubes.