I only have one bike and one wheel, so i don't have an extra wheel with cassette to switch out. I just bought new, cheap, hearty tire to wear down on my trainer. when i'm ready to ride outside again i'll put the other tire back on.

I always keep an eye out on performancebike to see if their deal of the day is a tire.

But the trainers do ruin the tires FAST. so just keep an eye out of the one you have on.