ok, i'm pretty new to this so i'm probably wrong...
The R2 tyres may need different pressure settings to the R1 to get them to work well...
you know n F1 this year, when you see them making adjustments to the tyre pressures at the stops, in order to alter handling and wear rates....
my point is if you are using the R1 pressure sets on R2s, this could be your problem...i dont know how to fix it though...