This shot of the 2010 Yamaha YZ450F is getting a lot of attention and rightly so. We can't remember having seen any reversed cylinder machines sold to the public since the 1990 Yamaha TZ250A privateer road-racer. Beyond the reversed single-cylinder, the new YZ450F looks to be an entirely new bike, with a slew of refinements including front and rear suspension, rear frame, new seat and we're guessing a completely revised chassis as well. While we think the Yamaha looks pretty cool and will be fast in the dirt, we're holding out for a supermoto version.
The logic behind the reversed cylinder is better weight distribution by pushing the crank down and forward in the chassis for improved handling as well as a cooler intake and a direct line of flow from intake through the cylinder to the exhaust port. This was also the criteria for the reversed-cylinder TZ250, which, if memory serves right, was known to be rather delicate, cracking motor mounts and causing water pump failures, chassis harmonics and vibration issues. Hopefully Yamaha has fixed all those gremlins this time.