There is a large "normal" range depending to the type of riding you do. If you're in the twisties, or the mountains, your rear tire wear is normal. Your front tire seems to be wearing faster than normal. At about 15000 miles I'll be replacing both tires, the rear for the 3rd time (fourth set), the front for the 1st time. (I started getting the cupping effect on the front tire at about 12k miles).