[MaSnaka]

Just a couple suggestings, that clean spot under your fender...spray it with some flat black spray paint. See if it gets rubbed off again. Also when the suspension moves the tire clearances are going to change as a result of body roll. 275/60/15 doesn't sound too oversized. Something I noticed with those same tires was that with 28 lbs pressure you will be slipping and sliding. Much better to keep the pressure low like you have it.
I hope this helps. Good luck.

John