I've made a small change to Jenease's chain line. The idler under my seat now is free to move a little to the right, or to the left, depending on whether I shift up or down. In short, a sliding idler. This had the great advantage that the relatively narrow ten speed chain runs better on the idler. Less noise, less friction, more efficient. Being optimistic, this could result in a speed increase of 1%. That's just me guessing, but it is well known that chains run less efficient when you deflect them sideways. This evening I did a short test ride, and it felt and sounded better.
The idler comes from Gingko, a German company. I've added a short piece of chaintube to the upper chain to guide the tube with with the return chain. Only thing left to do is change the chain keeper I've made. It's a little to close the chain now, and the edges aren't nicely round.