I have a set of reissue rat bones 90a that I can powerslide on. I have a set of 90a Oval Dragons that I can't powerslide on. Strange! I also have a set of black rat bones 2 that are 97a and a white set. The black ones seem harder and slide better than the white ones. Strange! Anyone else notice this? This is not meant as a complaint, I love all bones and powell wheels. They are the best.