Could someone aid my understanding of the factors involved here? The question that has been rolling (pun intended) around my mind is in regards to a trend in mountain biking. The new thing in MTBing is the 29" wheel. Standard wheel diameter is 26". Advocates of the 29er say there is less rolling resistance with the greater diameter wheel which enables them to more easily maintain speeds on trails with varying terrain (rocks, roots, logs, etc..). The thing is, as I understand it, a larger diameter wheel is heavier as are the bike components and bike frame (so as to accommodate a larger diameter wheel). This heavier wheel should create more resistance, requiring more power to accelerate it. The "lever" of the wheel is also longer on the 29" wheel which would make greater friction. So is the perceived benefit of the 29"wheel derived from the reduced angular momentum of a larger diameter wheel? Thanks for any replies.