How many of you who ride your YZ-F's MX and off-road have switched to an 18" tire? What's the primary issue with the 19" off-road? Flats? I'm not in a racing situation and when I get to rocks, I'm slowing down so I'm thinking the 19" should be fine for the 25% off-road riding I plan to start doing. The other 75% is going to be "easy" MX. Comments appreciated.