Chain management: Why so many chains? In designing this bike, chain management and chain noise were two major concerns. The first thing that I did was put the shifting where Shimano intended it to be, in the conventional BB location. The chain weight is what Shimano intended, so the rear derailleur works like it should and give you crisp shifting. This dictated that we make a spider to carry four chain rings so that the spider is driven via the inner most chain ring from the single chain ring on the crank set. By changing those two chain rings, we can over or under drive the spider to change the gearing (see Gearing, below). Then we put an adjustable idler sprocket behind the head tube to raise the chain above the fork and create shorter manageable lengths of chain, rather than one really long chain. This keeps slack chain weight to only what the rear derailleur is designed to handle and minimizes the chain noise. It may look complicated, but it is really quite simple and follows conventional wisdom in industrial design. |