Buying a used tire to carry as a spare?

This is one of those topics that comes up now and again. there are 2 schools of thought to this. Ones that would not be caught dead without a spare and some that use RSA and let them bring and mount you a new spare. Pros and cons to both. I am on the latter side of the fence and feel carrying a spare I may never need is not only a waste of money but a waste of space. When I can call coachnet to bring me a new tire and have them mount it. But that's the direction I chose. I imagine that's the majority since new coaches no longer come with spares or easy places to put them. But if you want to buy an old tire and let it sit in the bin then I imagine you'd want to buy it from a reputable shop and have it checked out. But how long do you keep it before you swap it out? Sitting un-used in a bin or not - it's going to age and lose air. When it comes time to need it you may find that either it may not be up to the task, or that it only gets you far enough to buy a new tire anyway. How long do you tempt fate on your used spare before you replace it? In which case now you've bought 2 tires. Despite RSA taking longer in remote places than others, I've never heard of anyone stranded indefinitely. I mean if you have to call RSA to change your spare, only to probably have to buy a new tire anyway, why not just have RSA bring you a new tire and save yourself the money you spent on the spare? The risk, I assume you are trying to mitigate, is RSA not being able to find your specific tire. Are they that uncommon? I mean you're going to have to find one anyway in pretty short order. Just not sure what the upside is.