I've attached a crude image of the point that confuses me. In the diagram, A is the chainring, B the cogs. C are the derailleur pulleys. I've shown a line (crudely tangential) that shows the effect of pulling the chain tight around the big cogs excluding the derailleur pulleys? Add 1 link to this. That's how I've been reading the thread so far. If that is the case, how does 'tight' + 1 link provide sufficient length for the pulley wheels? Granted, it is not wise to run big-big no more than you want to run small-small, but have I completely lost the plot? I think I have but I can't see it in the current discussion. Please explain.