Ideally, it should be possible to produce caravans for help building wonders without any waste. So I am wondering how this is best done. Say a city has an output of 22 shields. If I let it build the first round, I have to rush buy something so that 22 shields are left, i.e. I have to rush buy something with 28 shields for the caravan which requires 50 shields. Of course this is not possible, so I rush buy something with 30 shields, and live with the waste of 2 shields. I could also let the city build for two turns, ending up at 44 shields. If I rush buy the last 6 shields, they are wasted. So I have to let it run for one more turn, ending up at 66 shields of which the 16 are lost. So in this case, the optimal rush buy is buying the 8 extra shields after the first round to get 30 shields. Follow me this far? I guess there is not much point in rush buying a caravan from scratch, i.e. all 50 shields, even incrementally. It would be too expensive, of course depending on the hurry that you are in.
I often find myself in the situation that I have to remember building a wonder as soon as I realize that I need it. Letting a city start to build it is a good idea, for I might have many things to think about at the time, say in the middle of an unplanned war with the greedy greeks. Later the wonder can be built to completion by adding cash or caravans. Here, the Wonder Trick is wonderful, because I might start to build the wonder ahead of time, so that a significant amount of shields have accumulated at the time when the tech becomes available. I sometimes start building a soon to be obsolete wonder, because I expect that there will be a wonder that I'll want later on, and then most of it will be built already. You may say that I have a Wonder City in my plan.
As an example, in my last game I desperately wanted J. S. Bach at a time when I was forced to select researching Warrior Code. But the French got ahead of me because I didn't research Feudalism yet. I wanted J.S. Bach, because Railroad had been discovered, so my HG was not doing me much good. I had started building a wonder in a city that another city was already building near completion. I started doing that in a third city too. The French refused to give me Theology. I obtained Warrior Code from a pet Civ and completed reserching Railroad instead. Now being able to switch from the obsolete wonder to Darwin, I then obtained Feudalism and rushed Darwin with some cash. I got two new techs and finally got to Theology. Having the cash and caravans ready, I managed to build J. S. Bach in time to beat the French. I needed the two free techs, because I wasn't sure if I would be offered the choice of Theology next, not having kept track of the 0,1,2-rotation. If I had not gotten J.S. Bach, I would have to raise luxuries or build coloseums in most cities. When I later added Adam Smith to my list of wonders, having only cities with one gold improvements, I managed to have zero luxuries and zero costs. That meant that I could crack up research into 100% and pay nothing, which I thought was neat at the time.
