My experience is that the pads matter. Pads which need temperature won't heat up as much on a light car. It also matters how much of a braker you are. Mintex pads came with the ventilated disc kit for my Roadster, and gave me exactly this problem. On the rollers, balance was all over the place. On the road, it was evident for the first few seconds of application, then enough heat came in for them to work, but for my light use of brakes it didn't work. I went to Greenstuff, which were fitted whan I bought my Roadster on standard pads and no further issues. I realise that some hate Greenstuff. I also know that most find Mintex fine. For me Mintex did not work.