Sure, other four-stroke motocross bikes existed, but when it comes right down to it, Yamaha revolutionized motocross bikes when it introduced the first YZ400F in the late 1990s. Doug Henry took a version of that bike and won a Supercross main event (in Las Vegas) and an Outdoor National championship . . . proving to the world that four-strokes could work, and work exceptionally well, on a motocross track and a supercross track. You could say that the “beginning of the end” of two-stroke motocross bikes had arrived (although no one knew it at that point).
It took a long time for Yamaha’s competitors to fully respond to that ground breaking machine, but eventually they did, and Yamaha found itself knocked out of the top spot in the class. The Honda CRF450R was declared the new king by most motorcycle journalists a couple of years ago — a crown that Honda has yet to relinquish.
You could even say that the Yamaha YZ450F was getting “old in the tooth”. Last year, it was the only 450cc motocross bike produced by any Japanese manufacturer that retained a steel frame (both the Honda and the Suzuki RMZ450 featured aluminum frames). The motor, with various detail changes, had been around for quite a while, as well.
In 2006, Yamaha introduces an all-new YZ450F with the express goal of offering the best motocross weapon in the class straight out of the dealer’s showroom floor.
To take back the mantle from Honda, Yamaha began by redesigning the 449cc power plant. Although it is still a DOHC and features five-valves in the head, lots of changes were made to improve the quantity and quality of the power delivered by this light weight package.
No less than the piston, crankshaft, and connecting rods were redesigned inside the engine for increased durability and performance, with Yamaha also directing a spray of oil to the bottom of the piston this year. Still featuring titanium valves, the combustion chamber reaches a compression ratio of 12.3 to 1.
One big change is the addition of an additional gear in the transmission — the 2006 YZ450F now features a five-speed transmission. Although four-speeds were virtually always enough for a motocross track, the new five-speed answers a call from those riders using their YZ450F for more than motocross, including enduro, cross-country and desert racing. Previously, some of those riders needed to increase the final drive ratio to the point where first gear became overly tall (this is the only way to get enough top speed out of fourth gear in desert racing, for instance). The addition of a fifth gear is a welcome change that should not reduce the effectiveness of the bike on the motocross track.
The biggest news for 2006 is the new aluminum frame that combines cast, extruded and forged aluminum tubing to optimize frame rigidity, and that also repositions the engine for better mass centralization and improved handling. Unlike the competition, Yamaha’s aluminum frame is not a “perimeter” design. In fact, it appears to mimic, in many respects, the configuration of the old steel frame.
Like its smaller brother, the YZ250F, the 2006 YZ450F features Kayaba suspension components, including a speed-sensitive 48mm fork and a titanium-sprung rear shock (with a 2mm larger shock rod and a friction-reducing coating).
Engine changes are topped off with carburetion and exhaust changes for better breathing and even greater power. The cylinder head angle and the relocation of the dry sump oil tank inside the front of the crank case is said by Yamaha to improve the machine’s overall balance and handling (as well as eliminate external oil lines).
Our test rider Russ Somers (a pro-level vet rider who works for Team Simpson) had a chance to test the 2006 YZ450F at Competitive Edge Motocross Park in Hesperia, California. These are our first riding impressions of the new big Yamaha motocross weapon.
To begin with, this is the first track we have tested a 2006 motocross bike on that was not perfectly groomed before we arrived. For our test, the Competitive Edge track was riddled with braking bumps, acceleration bumps and chop. This gave the suspension on the 2006 YZ450F a real test. A test it passed with flying colors.
The revised fork and shock give the new aluminum chassis a very balanced, composed feel. The YZ450F was very stable on the higher speed, choppy straights, but also dropped into corners well and turned predictably. The new YZ450F does pretty much exactly what you ask of it.
The new engine also earned high marks. Very smooth and usable, but very fast, the deceptive power of the YZ450F had Russ overcook more than a few corners with unexpectedly high entry speed. The bike also had plenty of torque, because jumps right out of corners were cleared easily.
When every manufacturer is aiming for a smooth powerband in the 450 class, the new Yamaha YZ450F just might be the smoothest of them all. Vibration levels are low, and there is no hit anywhere to be found.
The new five-speed transmission is outstanding. Russ commented that he never felt unsure of a shift, and never missed one. The bike also shifts well under power. On this particular track, Russ did find himself between second and third gears on some corner exits (he would have preferred either a taller second or a shorter third).
Like the 2006 YZ250F, brake power and feel on the new YZ450F are excellent. The ergonomics of the bike, which features a stock Pro Taper bar this year, worked very well. The bike is slim, and easy to move around on.
The bottom line is that the 2006 YZ450F is “night and day” better than the old YZ450F. Is it better than the competition? That question is impossible to answer after a single day on the bike. It is clearly in the hunt for class leadership, however, and is unlikely to disappoint any buyer shopping for a new 450. It is a very balanced, refined package that reflects Yamaha’s unrivaled experience in this category.
U.S. MSRP for the YZ450F is $6,899.00 for the Team Yamaha Blue/White model and $7,099.00 for the 50th Anniversary Yellow/White edition. The 2006 YZ450F will be available later this month in U.S. dealer showrooms. Take a look at Yamaha’s web site for additional details and specifications.
