No other machine in the motocross world has a track record as impressive as the Yamaha YZ450F. Winning 14 out of 15 rounds in the 2006 MX1 World Championship, and dominating the early 2007 MX1 GPs, its superiority is in the record books for all to see.  However, while past victories are important, Yamaha is always looking to the future, and despite its outstanding success, the YZ450F has undergone a wide number of important changes for the new season.

With its broad spread of hard-hitting power, the YZ450F has established a reputation for being one of the fastest and yet also one of the easiest bikes to ride in a wide variety of track conditions.

At the same time, its Grand Prix developed chassis is widely regarded as offering a winning combination of outstanding handling and manoeuvrability, characterised by high speed stability and a light feel.

For 2008 season this MX1 class leader is subject to a number of significant improvements to the engine and chassis which are aimed at further strengthening the engine power feeling, while also reducing weight and fine-tuning the rigidity balance of the aluminium chassis, and thereby enhancing the YZ450F’s responsive and light feeling handling qualities.

YZ450F Engine

Reshaped intake ports
The YZ450F’s innovative 5-valve cylinder head design is one of the most sophisticated in the category, and plays a vital role in enabling this high-tech MX bike maintain its well-documented superiority on the race track. For 2008 the combustion efficiency of this advanced cylinder head is further improved with the introduction of reshaped intake ports which enhance the bike’s low to mid-range performance.

New exhaust camshaft profile
In order to optimise the significant performance gains of the new intake port design, the latest YZ450F’s 5-valve cylinder head is equipped with new camshafts featuring reshaped profiles. The inlet valve timing has been adjusted, the overlap is modified and exhaust lift is revised to create an idealised balance of intake and exhaust operations for increased combustion efficiency and improved performance in the important low to mid-range zone.

Yamaha YZ450F 2008

Reduced piston clearance
The YZ450F powerplant is already one of the most advanced 4-stroke engine designs in the MX world, featuring cutting-edge technology which gives it a real advantage. Extensive use of lightweight materials has enabled Yamaha to create a light, compact and high-revving engine which produces a remarkably wide band of hard hitting power – and for 2008 our engineers have further reduced cylinder/piston tolerances of the 95mm diameter piston in order to enhance the overall package.

These reductions may only be measurable in terms of microns, yet the differences are most definitely tangible, and include increased torque output, smoother running and quieter operation.

New 94dB silencer
Complying with the new FIM94dB(A) regulations is a new stainless steel silencer which maintains the machine’s strong low to mid-range power output, while reducing overall noise.

Revised transmission backlash
As well as reducing the tolerances between the piston and cylinder, Yamaha’s engineers have also reduced the backlash in the YZ450F’s transmission. Reducing the backlash between the primary gears and also within the balancer gear makes for better meshing, which also ensures even lower levels of mechanical noise from this high performance engine.

Yamaha YZ450F on the track

New engine colours
The uprated ’08 engine can be distinguished from its forebears by the new matt black engine covers which give a bold new look, while the cylinder head colour features a new shade of silver.

New carburettor settings
Revised carburettor settings are made for 2008 in order to complement the changes to the intake port, camshaft and silencer. These detail modifications ensure that the latest YZ450F delivers strong power combined with instantaneous throttle response that have become the hallmark of this dominant MX1 motocross bike.

Detail changes
In accordance with Yamaha’s policy of constantly upgrading components wherever possible, the latest YZ450F is equipped with a new aluminium inspection screw on the left side crankcase cover, as well as new crankshaft bearing stopper bolts.

YZ450F Chassis

New steering head pipe
In order to accentuate the YZ450F’s feeling of lightness and renowned agility in corners, the ’08 model features a new steering head assembly. The frame’s head pipe length is reduced by 5mm, as is the steering stem, while the forged aluminium lower triple clamp is all new. Featuring an ‘H’ shaped cross section, this new lower triple clamp is lighter than the previous design. These significant changes to the steering assembly make a real difference to handling performance by reducing weight while maintaining the idealised rigidity balance of the bike, giving a lighter overall handling feel for quicker turning.

Revised rear suspension assembly
Significant changes have also been made to the YZ450F’s rear suspension assembly in order to enhance the overall rigidity balance and handling performance of the GP-developed lightweight aluminium chassis.

A new specification titanium rear spring is featured for 2008, while the collar and shaft are redesigned, and the weight of peripheral parts has been reduced. In addition, the linkage ratio has been modified, and the net result is excellent shock absorbing characteristics together with optimum levels of traction.

At the same time the lightweight rear shock’s high-speed compression damping settings have been amended by altering the valving, and this change is designed to improve overall handling characteristics.

These rear suspension changes are designed to work in unison with the revised steering head assembly to enhance overall lightness, and in particular the ease with which the latest model can be leaned into corners.

the 2008 YZ450F runs with improved 48mm diameter Kayaba front forks

Improved front forks and lighter protectors
In order to maximise the handling performance advantages associated with both the new steering head assembly and the uprated rear suspension system, the 2008 YZ450F runs with improved 48mm diameter Kayaba front forks.

Newly-designed outer tubes feature a more compact oil seal housing design which helps to reduce overall weight for lighter steering characteristics. Additionally, the standard fork settings including the compression damping valving have been revised for the new season, giving improved damping qualities together with a smoother overall feel to the front end.

Unsprung weight is a key factor in the performance of any suspension system, and accordingly our designers have focused attention on this area. Newly designed left and right side fork protectors are featured, offering an unsprung weight saving of 120g to give an even lighter steering feel and even more responsive suspension action.

Compact new lightweight front brake assembly
The latest YZ450F is equipped with a new front brake caliper which reduces unsprung weight by 220g. This compact and lightweight design is the same system that was successfully introduced on the YZ250F for the 2007 season, and features a smaller diameter 22.65mm piston (compared to 27mm for 2007), and smaller pads, together with a new master cylinder piston, which is reduced from 11mm to 9.52mm, saving another 45g. As well as reducing weight, this compact new front braking system offers accurate feel together with strong and progressive stopping power.

The 2008 bike also features a new front brake lever design which offers greater adjustability, and the rear brake pad material is changed for enhanced braking characteristics.

New lightweight disc, axle and collar
Even more unsprung weight savings are achieved by the adoption of a new wave style disc featuring elongated slots rather than the ’07 model’s round holes. In addition, a new lightweight front axle and wheel collar take the total unsprung weight savings for the YZ450F’s front end to around 400g, to give a significant boost to handling characteristics and front suspension performance.

Wider footrests
Rider fatigue is reduced, and comfort is enhanced by the use of new wider 55mm footrests, compared to the 45mm design featured on the 2007 model. Manufactured from stainless steel, these new footrests are the same as those that have proved to be extremely popular on the WR450F enduro machine. The reduced pressure felt through the soles of the rider’s boots when landing from a jump is noticeable, and this contributes to the improved levels of comfort and operability of the 2008 YZ450F.

Pirelli tyres fitted as standard
For the 2008 season the YZ450F runs with Pirelli Scorpion MX MidSoft 32 will be fitted to the front and rear.

2008 YZ 450F

YZ450F Technical Highlights

• Reshaped intake ports
• New exhaust camshaft profile
• Reduced piston clearance
• New 94dB silencer
• Revised transmission backlash
• New engine colours
• New carburettor settings
• Detail changes
• New steering head pipe
• Revised rear suspension assembly
• Improved front forks and lighter protectors
• Compact new lightweight front brake assembly
• New front brake lever
• New rear pads
• New lightweight disc, axle and collar
• Wider footrests
• Pirelli tyres fitted as standard

2008 Yamaha YZ 450 F in White

2008 YZ450F - Technical Specifications

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