how many stem spacers with an aluminum steerer?
Lennard Zinn asked Trek and Trek said:
The number and placement of spacers does have an effect on the fatigue life of an aluminum steerer tube. Running less than 5mm of spacers under the stem can concentrate or "point load" a great deal of stress in one spot on the steerer. Therefore, Bontrager recommends a minimum of 5mm, and a maximum of 40mm of spacers between the stem and the headset to maximize the fatigue life of the steerer.
Scott Daubert
Trek Bicycles
See:
http://www.velonews.com/tech/report/...s/11432.0.html