Jon is onto something.
Indeed, a long head-tube implies a heavier rider. However, it would be interesting to compare bikes according to how much weight is on the front wheel. After all, the amount of weight on the front wheel is typically much less (maybe 66%) of the weight on the back wheel (60-40? 66-33?)
After Jon mentioned lubrication, it occured to me to think about the stresses on the headset cups.
If one used only light oil on the headset, then it would all drain to the back of the headset rather quickly, leaving the front unlubricated. And the front is under compression, i imagine, when the rider sits on the bike (the back is being stretched.) So just where the lubrication DOESN'T want to stay, is where the highest compression exists on the headset.
It would be great if one could make a 'ratcheting' headset that would turn continuously to the right. It would also be useful to create a front road brake that allowed the fork to spin 360 degrees (one could do it once before every ride.) It might also be good to consider adjusting the headset or facing the head-tube with a rider's weight on the bike, if that were possible.
- Don Gillies
San Diego, CA, USA