Originally Posted by luker
You won't stretch it that much. what stretching does, mostly, is give you a little clearance so that you don't make a huge mess on the sidewall when you put the glued tire on. storing good tubulars on a rim is also a good idea, as folded tires will eventually crack at the sharpest point of the fold. I don't have any good tubulars, so I don't worry about it too much...
Per instructions the glue is left on the tire and rim about 20 minutes after the initial application to dry to a tack then the tire is mounted so there is no mess on the side wall of the rim.
Perhaps storing a sharply folded tire is not a good idea; but stretching during storage seems like a worse idea. It is not wise to ride on a overly stretched loosely fitted tubular tire.
A spare spoked wheel may be useful to check repaired tubular tires as the tire should not be inflated without the support of a spoked wheel.
None of my folded spare tires have cracked while stored in the seat pack.
Perhaps your tires were affected by something else; such as direct sunlight or open air and changing temperatures.
I store my new unused tires loosely across two pegs in the basement. It's cool and dry in the basement and no direct sunlight shines on the stored tires. This method has worked for years without any problems.