Just replaced tyres at kwikfit today. Didn't have time to shop around as I discovered the Infinitys the car came with were splitting and the tread was becoming detached from the rest of the tyre! Anyway asked Kwikkfit to fit 205 45 R16 87W and they fitted correct tyre to the front (Michelin PS3) but they put 205 45 R16 83W pirrelli p zero on the back. I pointed this out and sled if okay and they said yes. On the way home the back seemed to be steering itself. Is the load rating critical or should Pirellis feel s**t compared to dangerous Infinitys? Help please- should I insist they change them?