My commuter bike eats chainrings. I have a 9 speed so a single chainring up front and nine in the back. It means that the chain angle is moving dramatically. It's not because my commute is hilly- its not- but urban commuting in Boston/New York means frequent times when I slow to walking speed and drop into the lowest gears to do so. Takes me a little under a year to wear one down to tiny pointed teeth.