Yamaha have released details of the 2009 YZ250F and the YZ450F

 

2009 Yamaha YZ250F and YZ450F

 Yamaha have released details of the refinements for the 2009 model YZ250F and YZ450F. Focusing on "tight curve performance", the 2009 model YZs feature a number of changes to the suspension components. Four position adjustable bars and a new seat design round things off. A Special Edition white YZ450F version will be available, complete with contrasting black rims.

New lightweight swingarm

To help create more linear cornering performance through improved concentration of machine mass, a new-design rear swingarm is adopted on the 2009 YZ250F and  YZ450F. The cross-section of the new swingarm is asymmetrical in its upper and lower portions and it achieved greater rigidity in the lateral direction compared to the existing unit. Also the cast parts of the pivot end have been redesigned for lighter weight. As a result, 350 g has been removed from the swingarm compared to the existing model. This combines with optimised suspension settings to bring cornering performance to a new level.

Since the 2002 models, the aluminium arms of the YZ series models have used parts manufactured with the hydro-forming method. This is a method that was chosen to provide greater “forgiveness” in the longitudinal direction and stiffer rigidity in the lateral direction and in torsional force resistance. In this method, hydraulic pressure is applied to the inner surface of the tubular aluminium stock to shape it to the optimum form. It is a method that takes advantage of the inherent metallurgic structure of the aluminium to maximise strength while achieving a smooth, highly precise part shape at the same time.

For production motorcycle parts, this method was first used for the 2002 YZ models and has since then its use has continued on the YZ450F/250F/250/125, and it is now used again for the 2009 models. To accommodate this new rear arm, the bracket that holds the rear brake caliper and the seal guard are also newly designed.

New-design rear hub and large diameter (25 mm) rear axle

In order to improve cornering performance by reducing un-sprung weight, a new-design rear hub that is 180g lighter than the existing unit is adopted. At the same time, a new large-type 25 mm  axle has also been adopted to achieve a more rigid feeling. This new rear hub is manufactured by a special high-vacuum die casting method. In this high-vacuum die casting method a vacuum is created in the interior of the die in order to draw the molten aluminium in under optimum conditions that reduce the occurrence of oxidised elements in the metallurgic structure, which increases the strength of the aluminium parts that are cast.

This added strength makes it possible to design a thinner walled hub. For this new hub, the hub bearing spec has also been changed. The outer diameter of the bearing has been reduced and the number of bearings increased from two to three to decrease weight while maintaining the same level of reliability. Plus this new rear hub contributes to more efficient use of space around the rear axle. The diameter of the rear axle has been increased from the 22 mm  to 25 mm to contribute to improved rigidity balance.. Also, in order to optimise the balance of the wheel and the newly designed rear hub, the angles of the spokes with regard to the hub have been changed to achieve a suitable amount of “forgiveness” in the wheel which aids traction.

New front suspension settings

For 2009, the settings of the front suspension have been changed with the aim of improving feel. In particular, the specification of the valve that creates the force has been optimised to provide a sure damping effect and a smooth, constant feel when entering a curve at high speeds.

New rear suspension settings

As with the front suspension, the settings of the rear suspension have been changed with the aim of improving operation by optimising the change rate of the link lever ratio and the valve that creates the cushioning force. This provides a sure damping effect when braking and a smooth feeling when entering a curve at high speeds. These changes in the front and rear suspensions combine with the effects of the lightened rear assembly to contribute to more linear controllability when cornering.

Adjustable bars (four positions)

Since the ’06 models, an offset axis is adopted for the handlebar bracket on the YZ450F/YZ250F. This made it possible to select between two different (forward and backward) handlebar positions by turning the bracket handle bar holder forward and backward. For the 2009 model, two attachment holes are provided on the handlebar crown (holder). This makes it possible to select between four different handlebar positions by combinations of the bracket handle bar holder side (forward and backward) and the crown side (forward and backward). This increases the forward and backward range of adjustment to enable settings that accommodate a wider range of rider preferences, course layouts and track surfaces.

New seat adopted

The base material of the new seat is a smooth nylon base material and composite vinyl chloride leather-look cover with optimised chemical makeup for just the right balance of hold and ease of sliding. Also the shape of the grain of the seat cover has been changed. The result is a seat that has both the ease of slip when the rider starts to shift his/her weight and the right amount of grip when it’s necessary to hold the machine firmly. The shape of the seat surface has also been changed to reduce build-up of sand or mud in the crevices in the seams and leaves the seat cleaner after riding.

Gold DID chain adopted

For the drive chain a lightweight, compact and highly reliable DID (non-seal) 520DMA2 chain is adopted for 2009. For this model gold type with a high-shine plating finish has been chosen. Besides outstanding durability it also provides a quality look that adds to pride of ownership.

Aluminium front brake hose bracket

An aluminium bracket has been adopted for the front brake hose for further weight reduction.

Adjustable clutch lever adopted

A new clutch lever holder that includes an adjustment mechanism is adopted. With a simple bolt operation the rider can adjust the lever to fit his/her taste. Also, the lever itself can be short-levered for lighter operability.

Special Edition colour available

In order to further heighten the pride of ownership, a white version of the YZ450F has been added as a second colour option. This white provides a sharp and refined image that adds value and includes a pair of trick black rims.

 Euro spec muffler adopted on YZ450F

YZ450F now features full power low decibel muffler (Euro spec type) which together with power bomb pipe produces high levels of power while keeping within MA noise limits

Light clutch operation YZ250F

The construction of the primary driven gear and housing for the clutch in the 2009 YZ250F have been changed to improve operation, with the damper spring being replaced by rubber. Also the judder spring has been eliminated and other specs altered to lighten the feel.

 

2009 YZ250F Specifications

2009 YZ450F Specifications