Gates
I have heard this tip but but have yet to try it myself. Apparently it works a treat, assuming you have a set of tyre levers to begin with.
The most difficult part of removing a tyre is breaking the bead (the seal that is formed once the tyre has been inflated a while).
Tip I have heard is to lay the wheel down on some soft ground and use the side stand from the GS or other heavy bike as your bead breaker. Carefully position the base of the side stand on the inner edge of the tyre by the rim and then let the bike lean over. the weight of the GS will easily break the bead.
From then on, its just careful use of the tyre irons. Also helps if the tyre is warm. A cold tyre will be a bitch to pry off.
Ferg