Ok, I give up. This is the first bike I've seen that has huge holes, about half-inch diameter at the rear triangle ends.
I would like to mount a rack, but these holes were made for something else. I asked the mechanic on duty at the local bike shop, he says they are for the disc brake setup.
I looked at other GT brand bikes and noticed the ones that have disc brakes are using the two smaller holes shown, so the guy had no explanation afterwards.
So, can anyone edumacate me on the purpose of having big-arse holes at these locations instead of the normal smaller holes?