After practicing some emergency stops, I find severe shuddering using either front brake or the rear, with little stopping power. I could actually stand on the rear brake and hardly stop, never mind locking up the brakes. The bike has 62k miles, I purchased it in March this year. I've put less than 100 miles on it so far, so I'm getting to know the problems just now. There are lots of suggestions on this site, but need advice on brands and procedures. I did replace the pads over the winter, but they are the typical Chinese parts. I'm guessing rotors, lines, better pads, calipers?