Always put the newer tires (with more tread) on the back. Understeer is better than oversteer. Most tire dealers won't put the new tires on the front for liability reasons. (I'm assuming the new tires went on the front based on your post.)
Mixing Tires | Using Different Tires | Michelin US
Winter Tech Information - Where to Install New Pairs of Tires?
Tires 101 on Better Tires, Front or Rear? :: Souza's Tire Service
Vic
Mixing Tires | Using Different Tires | Michelin US
Winter Tech Information - Where to Install New Pairs of Tires?
Tires 101 on Better Tires, Front or Rear? :: Souza's Tire Service
Vic