I installed some new (mechanical) disc pads a few days back and couldn't really get much stopping power off them, so save messing around I dropped at lbs for them to tune in. A friend picked it up for me today and I've just tried it out and to be honest there is barely any improvement! If I upend the bike and spin the wheel the brake works fine (perhaps a little slow to grip but reasonable). However, when I'm actually on the bike the brake is pretty useless still. I'm no whippet but 85kg is surely not such a ridiculous weight to render the rear brake ineffective is it? Is it s bedding in thing? Or is this just a myth?