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.