It's been a while, but I'm a bit stumped and figured I'd put a post out for some assistance / advice...

For the last 2 years I have been the happy owner of my Focus ST-2. I've owned her from new, and have had 2.5 years of trouble free motoring. At the last Ford service they pointed out that the two rear tyres were getting low on tread, normally I'd have replaced with the standard sport Continentals, however against my better judgement I went for a lower quality set on the advice of a friend.

Since moving over to the new rear tyres the general ride / handling feels awful. Initially I thought there was an issue with the ESP system as it seemed to be going off on nearly every corner - I took her back to Fords who said there were no issues with the system and that it was acting as designed. When I questioned about the ride, they said that it seemed fine to them :S

My question is as follows, could a cheaper set of tyres on the rear REALLY make this much difference? I only really use the car for general commuting, and dont really drive the car hard so would have assumed any standard tyre would be sufficient. Right now I am considering taking the car back to the tyre fitters and asking them to remove the recently fitted tyres, but I wanted to understand if there was anything else I should be checking first.

Any help here would be great.

Thanks,
Swanny