I replaced Air filter today. It was not as bad as I thought it would be. I just had to be careful about removing fairing pieces. At 4888miles, the original air filter was pretty dirty. I have been using my ZX for commute, back road fun and a couple of times to Yosemite but never off-road. I was surprised to see the old filter. My car's filter was very clean after 7500miles. I guess the difference came from how the air is sucked. In the case of ZX, air is sucked from the front side and cars inhale through a small pipe. At least, I don't have to worry about it for the next 5k miles