I take the extra tyre so that I have an extra one for my car at hand. You can get it put on the rim at most of the stops on the tracks. When I got the sidewall puncture near Oodnadatta, the spare wheel went on, then at the Pink Roadhouse, the extra tyre went on the rim of the punctured one and became the new spare and the punctured one went in the bin. You actually feel a little vulnerable when you are down to one spare out there. They don't always have one in stock if your size is not common. :) It would be a hassle to try and put it on yourself. You can break the bead with a high lift jack though.

