After the last 2 years I think I've came to the conclusion that it is suspension related. I had my suspension set(preload, compression, rebound, front and rear, no springs) at about 5k miles. My first 3 sets of tires(stock 56's Conti sport attack, bt016) didnt cup. My last 3 sets(Conti road attack, Conti sport attack, Q2) all cupped. I change my fork fluid once every year. So after 42k miles and almost 6 years im finally adding springs and having my rear shock rebuilt. hopefully I dont cup any more tires