Yamaha announced the 2005 YZ line today at the Yamaha dealer show in Las Vegas, and the big news is that the YZ125 and YZ250 two-stroke MXers get all-new aluminum frames for ’05. Yamaha’s take on the aluminum frame appears quite different from the design developed by Honda on its CR lineup – as you can see in the picture above. A combination of casting, forging, and extrusion was used to create a frame that Yamaha claims is a full 4.5 Lbs. lighter than the steel units found on the ’04 models.
The entire YZ lineup (YZ125, YZ250, YZ250F, YZ450F) gets new swingarms (claimed 1.1 Lbs. lighter), a redesigned rear linkage, Renthal aluminum bars, and Honda-style brake line routing for ’05. The YZ250 sticks with a revised version of the ’04 motor, while the YZ125 gets an all-new, 4-pound lighter motor inside its new aluminum frame. All these changes add up to a claimed dry weight (AMA weight method-all fluids, except fuel) of 217 Lbs. for the YZ250 and 196 Lbs. for the YZ125.
The four-stroke YZs stick to last year’s proven steel chassis, with both the YZ450F and YZ250F receiving revised settings and components for the forks and rear shock. Both the 250 and 450 also get new cylinder heads with redesigned intake ports and revised combustion chamber design, matched with reshaped pistons. Much effort was made to smooth the power delivery of the 450 in the low-end and mid-range. The YZ450F also receives revisions to the clutch and shifting mechanism for the new model year.