Rim wear. It depends on each rider's individual conditions (weight, terrain, stop lights, road grim, etc.) and you may not have had a problem with it. But my bike is only a year old and I'm starting to wonder if my front rim will last another 6 months. I can't be replacing a new front wheel every year and a half. So I'm thinking a front disc brake would be a good solution for me. But I'm going to pass on the rear disc.