Unusual Sidewall Wear on Spare Tire

[grill-n-go]

Got my first tire failure on the way home from the Labor Day weekend. Changeing a tire on I-95 in the mid-afternoon Florida sun - What fun!!

Attached is a picture of what my spare tire looked like after riding around under our TM for three years. If you look carefully you'll notice that there are wear marks at four points on the tire sidewall. I wonder if this wear will render a tire useless and if we should put something between the tire support and the tire to keep it from wearing like that. I might add that it got home (250 miles) but no longer its safe to use it.