I plan on taking a spare folding tire on my tour in the spring. If I destroy a tire along the way somewhere, the used tire will go in the rear and the new tire in the front, at which point I'll pick up another spare when the opportunity arises. Or if my rear wears out then I'll rotate the front tire to the rear and put the spare on the front. In whatever situation, I'd rather have the new, better tire on the front. In my experience, a front tire is more likely to slide out, and if a tire is going to slide out, I'd much rather it were the rear. Therefore, I keep the better tire in front.