nuclearfishin

I'm looking at a set of Cup 2 tires and was wondering if anybody knows what the difference is between the codes 305 /30 R19 102Y XL BSW and 305 /30 R19 98Y SL BSW FO? It says they both fit my car and the 102Y vs. 98Y is a difference in the load rating. Does anybody know what the FO means? The tire with the FO at the end is $63 more per tire. Any info appreciated. Thanks!