I have just changed to Pirelli P7s and cold mornings seem to make the wheel balance out of wack. I've never experienced this before and the retailer is (apparently) finding out from Pirelli if the cold is causing the tyre to reshape and potentially causing a "flat spot" until they warm up. Has anyone else come across this before? The wheels are balanced properly as they seem to be fine when it's warm, I'm just not sure if there's something else in the car that could cause a shake which appears identical to a poorly balanced wheel.

My car has 225/45 R17s on it. Any clues? I can see a few others have these tyres so I assume it shouldn't really be the tyres unless these particular ones are faulty.