Below is a copy of Xin Yu's posting:

Here's my theory. I have only played a couple of games so I'm not sure if it works.
Part I, using one food caravan and one commodity caravan
Suppose you have established 3 trade routes, and your city screen looks like:

-----------------------------
Supplies: (Salt)(Dye)(Silver)
Demands: Spice (Coal) Hides

London Salt: +7$
London Dye: +7$
London Silver: +7$
-----------------------------

If you send a food caravan to London, you get to supply Salt again:

-----------------------------
Supplies: Salt(Dye)(Silver)
Demands: Spice (Coal) Hides

London food: -1f
London Dye: +7$
London Silver: +7$
-----------------------------

Then you send a salt caravan to London you get back to

-----------------------------
Supplies: (Salt)(Dye)(Silver)
Demands: Spice (Coal) Hides

London Salt: +7$
London Dye: +7$
London Silver: +7$
-----------------------------

Here's how it works: A new trade route always replaces the first existing trade route if there are 3 routes already existed. For the source city, IF THE OLD FIRST TRADE ROUTE HAD THE SAME COMMODITY AS ONE OF THE SUPPLIES IN PARENTHESIS (example, salt in the above case), then the supply will come back. In the above case, you can keep on sending a food caravan to London then get to build a salt caravan, until the trade route no longer shows Salt as commodity:

-----------------------------
Supplies: (Salt)(Dye)(Silver)
Demands: Spice (Coal) Hides

London Beeds: +7$
London Dye: +7$
London Silver: +7$
-----------------------------

You will not likely to get salt back now so you should try your luck in another city. Remember you will much less likely to get Dye or Silver (the 2nd and 3rd trade routes) back by using the above technique.

Part II, using two commodity caravans

Suppose, before establishing your 2nd trade route, you first send a food caravan to your trade partner city, you will make the food trade route be the 2nd trade route so it will never be replaced (unless you go to another city). After establishing your 2nd commodity route your city screen looks like:

-----------------------------
Supplies: (Salt) Dye (Silver)
Demands: Spice (Coal) Hides

London Salt: +7$
London food: -1f
London Silver: +7$
-----------------------------

If you send a dye caravan to London, you get to supply Salt again:

-----------------------------
Supplies: Salt(Dye)(Silver)
Demands: Spice (Coal) Hides

London Dye: +7$
London food: -1f
London Silver: +7$
-----------------------------

Then you send a salt caravan to London you get back to

-----------------------------
Supplies: (Salt) Dye (Silver)
Demands: Spice (Coal) Hides

London Salt: +7$
London food: -1f
London Silver: +7$
-----------------------------

Compared to the technique in part I, You lose the benefit of one trade route each turn, but you get to produce more commodity caravans. Should be a good deal.

Note: In both games I played Salt and Dye were not demanded by the trade partner city. The technique might fail to work if the commodities were demanded.
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Copied by SG(2) Written by Xin Yu

After you discover trade, have your fingers crossed and look for hides as a supply commodity. If that happens (chance is high actually), you can save the food caravan. Just make sure that you do not send hides to a foreign city first.

-----------------------------
Supplies: Salt Hides (Silver)
Demands: Spice (Coal) Dye

London Silver: +1$
London Hides: +1$
-----------------------------

Silver is most likely to stay longer as a supply commodity so you send that one first. If you want to be safe, do not send out the third commodity yet. You can keep on building Hides caravans -- this one will not run out.

After a while the hides are gone and your screen looks like:

-----------------------------
Supplies: Salt Dye (Silver)
Demands: Spice (Coal) Hides

London Silver: +2$
London Hides: +2$
-----------------------------

Now you send a salt caravan and a dye caravan to London you get silver back:

-----------------------------
Supplies: (Salt)(Dye) Silver
Demands: Spice (Coal) Hides

London Dye: +2$
London Hides: +2$
London Salt: +2$
-----------------------------

From now on it's Dye and Silver dance:

-----------------------------
Supplies: (Salt) Dye (Silver)
Demands: Spice (Coal) Hides

London Silver: +4$
London Hides: +4$
London Salt: +4$
-----------------------------

Because Hides stays as the second trade route, you will not likely to run out of commodity. For example, after a while, when you trade the dye, it just disappears. However you can still do a gold-silver dance:

-----------------------------
Supplies: (Salt) Gold Silver
Demands: Spice (Coal) Hides

London Dye: +6$
London Hides: +6$
London Salt: +6$
-----------------------------

Testing was conducted in an actual game (Deity/Large World/MPGE)

For several years Orleans had produced no new commodities. So a food freight was sent to Paris.

PARIS (37)

Supplies: Salt (Coal) Hides
Demands: Copper (Dye) Uranium
Besancon Dye +16
Besancon Beads +16
Le Boulou Gold +16

ORLEANS (19) Before Food Freight

Supplies: (Salt) (Gold), (Gems)
Demands: Copper, Dye, Coal
Paris Gold +20
Paris Salt +20
Paris Gems +20

ORLEANS After Food Freight:

Supplies: (Salt) Gold, Dye
Demands: Uranium, Gems, Oil
Paris Food -1
Paris Salt +20
Paris Gems +20

OR (after a reload - a different outcome)

Supplies: (Salt) Gold (Gems)
Demands: Copper, Dye, Uranium
Paris Food -1
Paris Salt +20
Paris Gems +20

I will keep experimenting.

Were your tests done early or late in the game?

-----------------

SG(2)

Very clever!

The more I look at trade routes, the less I understand how supplies and demands are "tied up".

I never thought of using a food caravan to free up commodities.

It seems illogical that City A would eventually get "London Beads: +7$" when City A never supplied beads and London never sent City A a bead caravan. However I certainly believe this happened to you. The trade route system is just crazy!

Not a mistake; it was my misinterpretation.

quote: ----------------------------- Supplies: (Salt)(Dye)(Silver) Demands: Spice (Coal) Hides London Beeds: +7$ London Dye: +7$ London Silver: +7$ -----------------------------

Ahh, I see. If you find yourself in the situation shown in the Beads table (which is unrelated to the other tables) then you're screwed. This is because (rule 1) if you have three permanent routes and all are of equal value (and they are in this table) then a new route of equal value will always replace the first route (the one listed first, not necessarily the oldest). You can't send another "real" caravan since all your supplies are "tied up"; you must send a food caravan. Since (rule 2) food routes are always equal in value to the city's current best route a food route would replace one of the existing ones (the first one in this case due to rule 1). But in the Bead example, you sent a bead caravan sometime in the past. Now beads are no longer one of your supplied commodities. Since then you've sent a Salt, Dye, and a Silver caravan - all of which became "tied up" as supplies. When you knock off the bead caravan with a food caravan, you aren't freeing up any of your currently tied up commodities. And I bet two or more food caravans would just replace earlier food routes since the food route would be first on the list. Drat! All you can do is wait for City A's supplies to change on their own.

This is in contrast to your Part III example:

quote: ----------------------------- Supplies: (Salt)(Dye) Silver Demands: Spice (Coal) Hides London Dye: +2$ London Hides: +2$ London Salt: +2$ -----------------------------

Here we're very happy that a commodity that's no longer a supply is on our permanent route list. New routes to London will replace the first route only, always leaving hides in the second slot as a permanent route. As long as hides is a permanent route, at most two of your current supplies can be tied up. There's always a third for building! (Note: All three are (potentially) temporarily tied up while the third is in transit on a caravan. Also Note: Of course, all bets are off if we send caravans to a city other than London).