Hi!
It sounds as if the tire in question has a wire bead ("rigid" construction), and has been folded over on itself. Yes, it can be used as a touring spare. I've done so myself, and tires rolled this way store nicely atop a rack-top load, or affixed to the side of a pannier. In the "olden days" (pre-Kevlar beads) this was a common way to carry a spare tire. Ian Hibell surely used this method, as shown in many of his photos -- there was no other way! Some people would actually weave the spare through the space around the hub and between the spokes; this was pictured in a Sierra Club (US-based hiking, outdoors club) publication from the early '70s; Barbara and Larry Savage (See:
http://www.amazon.com/Miles-Nowhere-Round-Bicycle-Adventure/dp/0898861098 for a good read!) did this too, but I wouldn't recommend that for a number of reasons (imagine if the thing flipped out and caught a fork blade. Doesn't help wheel balance or rotating weight, either). You'll be fine with it atop the load. Just be careful to secure the looped tire so it won't <pop> open (a couple toe straps will do nicely) and you'll be fine.
Yes, if the tire has been twisted this way for awhile, it will be distorted when first opened. I would suggest opening it up to full size and straightening the bead with your fingers and storing it "open" till you need to depart, then re-twist/fold it for the trip*. If you haven't done the twist before, it is easy -- preferred method is to hold the tire at opposite sides with your arms crossed, then pull your arms apart. Like magic, the tire will collapse and the top and bottom fold over each other.
A true folding tire has Kevlar beads that allow several advantages:
- The Kevlar bead is lighter than steel, so the tire's weight is less overall. Rotating mass is reduced, and the wheel feels a bit livelier as a result.
- The Kevlar bead doesn't distort (bend/deform) as much in folding, but the tradeoff is they're sometimes a bit harder to mount.
- The tire truly folds over itself across the length of the tread-- and folds fairly flat and the same width as the tire, rather than overlapped. This allows for easy, compact storage inside your bags, rather than atop the rack or load. You could easily store two -- possibly three! -- folding-bead tires in the space taken by a roll-twisted rigid tire. Placed inside your bags, the true folding tire is protected from weather and abrasion that can cause deterioration over time. For a shorter trip, it doesn't matter.
On the downside, a true folding tire with flexible bead costs more than its rigid, wire-bead counterpart.
For use as a touring spare, there's no practical difference between the two as far as the bicycle is concerned, except for the additional rotating weight attributable to the heavier wire bead and the amount of space taken in storage. Pic below shows one neatly stored outside a front pannier on my old Miyata 1000LT.
Hope this helps!
Best,
Dan.
* As an aside, I store my unused tires in a garbage bag with the air squished out and top tied tightly shut. This then goes top-down into another garbage bag treated the same way. The bagged tires are then stored in a cool, dry place in my garage. Storing tires like this has kept them fresh for a long time. I recently opened a pair for the tandem, and they're fresh as new after 7 years, with no sign of rot, hardening, or ozone-checking. Not a bad way to go if you wish to keep your spare in good shape, ready for the next tour.
