The history of motocross is one replete with revolutionary designs, followed by consolidation and refinement of the dramatic motorcycle advances.
The move from big thumpers to lightweight two-strokes defined the 1960s. In the ’70s, it was long-travel suspension. The ’80s brought us liquid-cooling and linkage suspension. The ’90s heralded the return of the four-stroke (not coincidentally, the Yamaha YZ400F), and the ’00s saw the thumpers return to dominance.
Yamaha, with the all-new YZ450F, has fired the first shot in the war to rule the ’10s. This groundbreaking motocrosser features technical innovations that are highly desirable in the dirt, and may have implications for street bikes in the coming decade.
The most obvious advance, of course, is the new powerplant with a cylinder that is tilted over eight degrees backward from vertical.
One may be forgiven for thinking that the centralization of mass was the sole reason for this radical redesign. However, the answer is more complicated than that.
While positioning the YZ450F’s cylinder’s weight closer to the center of the bike has undeniable handling advantages, the cylinder is also off-set 12-degrees forward from the centerline of the crankshaft center-something that was made practical by reclining the cylinder.
In this location, the connecting rod is farther along in its rotation when the spark fires; instead of the rod being at an angle when power is produced, it is vertical, resulting in a more efficient engine thanks to less friction restricting the piston.
Multiplying the advantage, Yamaha was able to reduce the length of the rod, increase the bore, and shorten the stroke. The result is a smoother power delivery and an improved throttle-to-wheel feel.
Again, handling sees gains as the height of the motor is reduced, putting less weight at the bike’s extremities.
Fuel injection is not exactly new, but Yamaha’s engineers have leveraged the technology to make radical changes.
The intake of the YZ450F is at the front of the motor, and the exhaust flows out the rear. The Keihin fuel injector is at cam height in the front of the bike, with the lightweight air filter taking up space traditionally used to carry heavy fuel.
Now, the fuel cap is at the very top and front of the tank, with most of the high-octane, along with the in-tank fuel pump, being placed under the front of the seat.
To get adequate exhaust length, Yamaha designed a "tornado-style" exhaust header that makes a 360-degree loop between the exhaust port and the muffler. A tumor-like bulge at the beginning of the pipe is claimed to save one decibel of sound output without compromising performance.
Gearhead talk is interesting, but technology is here to serve us, so it must produce results. In the case of the YZ450F, the engine has established itself as a star. Push the kickstarter through its arc with a firm, not fast, push and the no-battery EFI system works its magic. The bike quickly settles into a predictable idle, just like a street bike.
Our initial testing was at the impressively sprawling multi-track complex at Milestone Ranch MX Park in Riverside, Calif., and average riders should be aware during the first excursion onto the track that the YZ450F’s motor demands respect.
Power is developed quickly off idle, and there is little resistance to revving; there are no hitches in the powerband, so your speed is fully determined by your willingness to twist the throttle.
Tabletops were used to quickly establish the YZ’s jumping credentials, and then doubles were instantly conquered without trepidation. The YZ is fully neutral in the air and lands without drama, self-correcting for minor rider errors.
In the corners, Yamaha’s chassis redesign reveals itself. With its weight centralized and ergonomics compacted, the YZ450F feels remarkably light when pitched over.
Taller engines make it difficult to both get the bike off vertical and pull it back up, and the YZ effectively minimizes that undesirable feeling. The new seat allows you to get up on the front wheel, so the Dunlop front tire shows no interest in pushing.
You pick the line, and the YZ follows it for you. If you like to square off turns for block passing, the bike has the binders to slow you down, the maneuverability to keep you on the track, and the power delivery to consolidate your gain.
Yamaha’s new aluminum chassis is made of 16 components and four types of aluminum rendering-cast, forged, extruded, and hydro-formed extruded.
Again, that’s great for discussion, but it also makes the YZ highly predictable in the whoops. You can dial in the power precisely; once you become accustomed to its aggressive nature, you can skip the whoops with confidence. Large, stock pegs provide a stable platform for all on-track obstacles.
Suspension on the YZ450F is comparable with the rest of the chassis. The KYB forks are speed sensitive, so they work well everywhere on the track.
Yamaha stiffened the swingarm for a more precise feel, and the shock has been moved to the center of the bike laterally, and closer to the center longitudinally, with the latter made possible by the repositioning of the airbox.
In both the front and rear, we find the standard damping settings to be perfect for a variety of riders out of the box-only the sag needs to be personalized.
Speaking of personalization, Yamaha sells a GYTR Power Tuner that plugs into a port near the steering head. Self-contained, hand-held and powered by a pair of AA batteries, the Power Tuner allows the rider to make significant changes to the fuel and ignition maps.
There are nine different adjustment points for each, and the Power Tuner allows for nine presets which can be entered without the unit being plugged into the bike. These adjustments can be instantly felt and customized for different tracks and changing conditions throughout the day.
Additionally, the Power Tuner allows you to monitor a variety of functions, including engine running time, self-diagnostics, error codes and the standard variables used by the EFI system.
Although offered as an official Yamaha Motorcycle Accessory, consider this to be an essential part your YZ450F’s toolbox.
D.H. Lawrence advised us, "If you make a revolution, make it for fun." He also suggested that we "kick our heels like jolly escaped asses." One wonders if the engineers of the 2010 Yamaha YZ450F were disciples of the early 20th century poet. Excuse me while I go out for some heel clickers. (Reid Davis contributed to this motocross test)
Motocross Riding Apparel
- Helmet: Arai VX-Pro3
- Goggles: Oakley Mayhem MX
- Jersey, gloves and pants: Shift Faction
- Boots: Alpinestars Tech 10
Photos by Don Williams at Milestone MX