Cord showing near bead What could be causing this? Tires are about 200 miles old. Used almost exclusively on smooth, cleaned asphalt. Sometimes gravel. 

Also - is the tire still safe?
I suspect that your brakes are misaligned &amp; are rubbing on the tire.
The brake pad should be centered on the rim braking surface, look closely &amp; you will likely see that the pad contacts the tire when the lever is pulled.

Not only does the pad touching the tire wear out the sidewall, but it also generates heat which damages the tire &amp; inner tube which could cause a catastrophic blowout.

I would fix the brakes &amp; then immediately replace the the tire(s).