Yamaha revealed the 2008 YZ450F and YZ250F
These four-stroke motocross machines feature significant changes over last year’s models. Described below are the major changes for each model. The one change that stood out for us was the huge bump in compression for the YZ250F (from 12.5:1 to 13.5:1). In addition to the traditional Yamaha Blue, each bike will be available in a white/red color combination for 2008.
Yamaha 2008 YZ450F- Revised intake port shapes, and revised intake and exhaust cam profiles increase combustion efficiency for improved torque and throttle response in the low- to mid-rpm range.
– Micron-level adjustment of piston external diameter minimizes piston-to-cylinder clearance for reduced vibration and mechanical noise.
– Adjustment of gear backlash between clutch primary gears and balancer gears achieves further mechanical noise reduction.
– A new, larger-diameter titanium exhaust header with revised taper characteristics enhances exhaust efficiency.
– First “punched cone” muffler ever on a production bike allows 35 percent length reduction and 270-gram weight reduction while meeting AMA noise regulations.
– Matte black crankcase covers: light, strong and cool-looking.
– Steering head pipe and steering stem are 5mm shorter; lower forged triple steering clamp is lighter—for enhanced handling feel. Swingarm pivot stiffness is revised to complement front-end changes and further lighten and improve steering/handling.
– Changes to the shape of the outer fork tubes and revised internals result in improved damping and a smoother ride.
– Optimized linkage ratio provides a smoother ride and enhanced rear wheel traction.
– New, YZ250F-style, front-brake caliper (-220 grams) and a lighter disc remove unsprung weight and provide excellent stopping power. A new axle and collar remove additional weight.
– A 120/80-19 rear Dunlop D756 knobby replaces the 110/90-19 for even more traction. A D742FA replaces the D739FAL front tire.
– Wider footpegs provide excellent boot traction and rider comfort.
Yamaha 2008 YZ250F
- A redesigned piston bumps compression ratio from 12.5:1 to 13.5:1, further exploiting the inherent efficiency of the five-valve combustion chamber. Carburetion and ignition revisions complement the increased compression.
– Adjustment of gear backlash between clutch primary gears and balancer gears reduces mechanical noise.
– Changes to the clutch boss and primary driven gear improve clutch oiling for excellent durability.
– Matte black crankcase covers: light and cool-looking.
– Changes to the shape of the outer fork tubes and lower triple clamp, and revised fork internals, result in excellent handling, great damping and a smooth ride.
– Optimized linkage ratio provides a smoother ride and enhanced rear wheel traction.
– 55mm stainless steel footpegs replace 45mm ones for great grip and comfort, and a new brake pedal eases operation.
– Grippy new Bridgestone knobbies front and rear.
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