we sold some tretreads for a while and I found the quality varied quite a lot - really depended on what the original carcass was . if it was a michelin , pirelli , metzeler dunlop or bridgestone then the chances were it would be OK , if the original carcass was a cheap nasty one then the resulting retread would be rubbish as well. So it pays to look through the tires and try to identify the ones made on good carcasses
Also I found that some of the retreads would have the tread put on crooked and then the tire would wobble around and give the same sensation as being flat.
I don't think anyone is selling them here in NZ anymore