two? Depends on what unsupported tour means to you, but to me, thats overkill and not what Ive done on long trips (1 month, 2 month) One more tire worth more weight and space.
On what sort of trips have you carried two spares?
You got me. I started late and have only done week long unsupported tours. I carry one folding tire, two tubes, a reinforced gasket material boot and a patch kit all of the time. I was giving the OP options, you?