Thank you, again, all. It's really too much! I am expanding like mad, and keeping my research between 50 and 80, usually nearer to 60. If it goes over 80, I have three cities build a settler team. For me, that's defensive unit, offensive unit, worker and settler - a ready made city. Though one thing still puzzles me. Many of you have said that it is not the percentage geared toward research, but rather the number of beakers created. While undoubtably true, I also notice that when I move from 90 percent to 60 percent, something that takes me 5 turns to research now takes me 11. So, percentage does matter? Just not as much as having many large cities producing beakers, I guess?
It's all about maintaining a balance between gold produced and gold spent, while producing as many beakers as possible.
There are many gold sinks in the game. The primary two are maintenance on cities, and maintenance on units.
Maintenance on units is easiest to reduce: keep the number of units down, and keep them in your cultural borders. Of course, you don't want to have so few units that your neighbors think you're an easy conquest.
Maintenance on cities is harder to reduce, and comes in two components: distance from a capital, and the number of cities you have, and they increase based on the population of the city. The easiest way is to build the Courthouse building, which halves the maintenance in your city. Keeping your cities close to a capital (your Palace, the Forbidden Palace, or Versailles) helps keep the distance cost down, and State Property civic eliminates it completely. Finally, keeping the number cities you own down helps reduce the number of cities cost.
Gold can also be spent on rushing buildings and upgrading obsolete units to modern ones, but you usually only want to do that with veteran units. It's often easier, and far less expensive, to build a new unit to replace an obsolete unit than it is to upgrade it.
Gold is produced in a variety of ways. First and best is shrine income. Some specialists also produce gold, and certain wonders as well. Finally you can convert commerce into gold. Buildings can increase the amount of gold a city produces.
If the gold you spend exceeds the amount of gold you can produce, and you have no gold saved at all, your whole empire shuts down economically. That's not a good thing.
Finally, there is the number of beakers you produce. There are many sources of beakers: commerce converted into research, specialists, and Wonders. Usually, your biggest source is the first one, which is why you want to keep your science slider high. Buildings can also enhance the amount of beakers a city produces.
Over expansion is the single greatest threat to a working empire. Lowering the science slider naturally reduces amount of beakers produced in each of your cities, which in turn naturally slows down your research, sometimes to the point of stagnation. Adding a city
can increase your beaker production, but only
if the potential research from the new city exceeds the beakers lost from your old cities, because they had to swap beaker production to gold production to help pay for the increased maintenance costs. Learning to do that is tricky, and takes experience.
Let's take the classic six city empire. Numbers are completely meaningless except as illustration. Your research slider is at 70%, and your happiness cap is eight.
Your capital is size ten. It is working three food tiles, three production tiles, and four commerce tiles. It has +4 food, +14 hammers, and +20 commerce. It is producing +6 gold and +19 beakers thanks to a library. Maintenance is -4 gold (-0 distance, -4 cities, no courthouse)
Your military production city is size eight. It is working four food tiles, and four production tiles. It has +3 food, +20 hammers, and +4 commerce. It is producing +1 gold and +3 beakers. Maintenance is -2 (-1 distance, -3 cities, courthouse)
Your Gold production city has the Shrine to Confucianism (+6 gold), and is also size eight. It is working five food tiles, a production tile, and supporting two merchants. It has +2 food, +5 hammers, and +4 commerce. It is producing +16 gold thanks to a market, and +3 beakers. Maintenance is -2 (-1 distance, -3 cities, courthouse)
Your Super Science city is size eight, and plays host to the Great Library. It is working one food tile, a production tile, and six commerce tiles. It also has two free scientists. It has +3 food, +5 hammers, and +32 commerce. It is producing +10 gold, and +32 beakers thanks to a library. Maintenance is -2 (-1 distance, -3 cities, courthouse)
Science city #2 is size six. It is working one food, one production, and four commerce tiles. It has +3 food, +5 hammers, and +20 commerce. It is producing +6 gold and +16 beakers thanks to a library. Maintenance is -3 (-1 distance, -2 cities, no courthouse)
Science city #3 is size five. It is working one food, one production, and three commerce tiles. It has +3 food, +5 hammers, and +15 commerce. It is producing +4 gold, +14 beakers. Maintenance is -4 (-2 distance, -2 cities, no courthouse)
Your military and civic costs are -5 and -13 respectively.
Net: +43 gold, -35 gold, and +87 beakers. Since you're at 70%, you might be able to afford a new city, so you do so.
With your seventh city, the number of cities maintenance costs in all your cities increases, by -2 gold, which increases your total maintenance costs to -43. Your new city also has a maintenance cost of -5 gold (-3 distance, -2 cities) which brings it up to -48. You're now running in the red, which causes you to decrease your science slider to 60%. This costs you -10 beakers in exchange of +8 gold.
You will need to either work four new commerce tiles (average of 5 comemrce at 60%) before your research regains its old levels... and new cottages need a long time to mature before they even reach that level.
Thankfully, between science #2 and #3, and your new city, you have the potential to work another eight commerce tiles, so once your new city and new cottages mature, you will have more research than when you started. Another option would be to scrounge up another +5 gold from somewhere (by building new courthouses or selling resources to your neighbor) to return your research level to 70%.
Now you immediately add an eighth city. Number of city maintenance costs increases by an average of -3 in all your cities, and the new city adds an additional -6 maintenance, for a total of -18. Since you have to drop your science slider to 40% to pay for all this (at a -20 loss of research,) you now have to add another twelve new commerce tiles before research can return to its previous levels. Unfortunately your new city only has the potential to work six new ones at this time, so despite adding a new city, you're actually hurting your research in the long run. You could also try to scrounge up more gold to increase your science %, but that isn't as easily done.