From www.motorcycledaily.com As expected, Yamaha will introduce aluminum-framed YZFs next year, in both 250cc and 450cc displacements. As a result, expect Yamaha to have the lightest four-stroke motocross bike in each class. Just a couple of years ago, it was difficult to believe that four-stroke motocross bikes could be as light as the two-strokes they compete against. A 250cc four-stroke as light as a 125cc two-stroke motocrosser? No way, we thought. Not with those overhead cams and valves that the lower displacement two-stroke can do without. Expect Yamaha's 2006 YZ250F to weigh roughly 211 lbs with fluids (empty gas tank). Still a bit heavier than the 125cc two-strokes, but only by a few pounds. Amazing. Likewise, the YZ450F should leapfrog the Honda CRF450R to become the lightest bike in the class next year with its new aluminum frame. Looks like someone is tired of seeing their marketshare being erased by the copycats.