Two of my bikes have biopace chainrings and when spinning the crank on the repair stand I can observe only a slight bit of possible rear derailler motion if any. If you look down while pedaling the chainrings are obviously "out of round" but there isn't nearly as obvious a motion in the chain tensioner function of the rear derailler. My limited intellect has trouble with the effect of chainwheel shape plus the number of teeth. However, if I think about an extreme case such as an almost bar shaped chainwheel, the effect seems more obvious. Such a chainwheel would result in pronounced "power pulses" to the rear wheel. The effective diameter of the chainwheel would change drastically as it spun as would the number of teeth engaged with the chain. However, I suspect the two effects would cancel out to a great extent as far as chain slack is concerned. Does anyone else think this is the case? Does anyone care at this point?