Never underestimate the power of small changes. Modern motocross race bikes are refined to the point where a little flex here, a touch of stiffness there, a millimeter at one end or the other and a few tiny valving shims can remake how a bike feels. It doesn't seem to matter how long the list of changes are; what counts is the result when the knobs reach the dirt. Yamaha's new-for-2006, aluminum-framed YZ450F was a fine machine and an able clan chief to the historic YZ-F line. The return to a five-speed and controlled but vigorous power wrapped in a solid-feeling aluminum alloy chassis highlighted the package. It missed the target in turning and steering accuracy, though, and the riding position made tall guys look like a pocket knife with the blades half folded. Yamaha calls '07 a refinement year. The new forged triple clamps (instead of cast) are more than strong enough for the job but have fewer ribs hidden underneath. The 1.5mm-longer shock is another shot at the turning gremlins, and a hit. The exhaust note is much quieter, and the cam timing is more radical. The result is a total package very different from a stock '06.
Chassis and suspension changes combine to take the curse off of impacts and allow the front wheel to follow the terrain more readily. And that even helps the steering feel. The bike rides higher in the rear and puts more weight on the front wheel. For sure, the steering is better but still not the stickiest in the class. More important, though, is the overall feel of the bike. All 450s have grown to be more like the two-stroke 500s of bygone days. In other words, they have more power than is optimum for the suspension performance and more than what a vast majority of riders need. That much power has a negative effect on suspension performance and handling, and it makes riders want to cruise turns and fireball straights. The '07 YZ450F has regained a nimble feel close to that of a 250cc-based bike with chassis updates and changes to the power character. But more about the power later. It flicks easily side to side and feels quick on its feet. The suspension offers a nice balance of stability, control and bottoming resistance. Braking chop and acceleration hack are handled easily for the most part, and so are hard landings from long jumps. Get out of rhythm, though, and start barging into jumps and bumps, and the fork feels like it uses too much travel too easily. The titanium shock spring is amazingly light but also feels relatively soft. The sag was close to maxed out for a 175-pound rider. Changing it for a stiffer unit is over $500 unless you opt for an aftermarket steel spring.
As positive as the chassis upgrades are, we weren't as sure of the engine. Yamaha made laudable efforts to quiet the exhaust note, and it worked. The bike is pleasantly subdued soundwise. A more aggressive cam is also in place, and it makes the bike very lively from one-third throttle on up, but the engine is much smoother below a third. On the sandy loam at Racetown 395, the power felt sharp and snappy with a quick-revving and free feel to the boost. On the ripped and watered desert dirt, the rear wheel spun easily, and the power felt controlled but strong. Then we hit the packed afternoon surface of I-5MX. There, with more grippy dirt, the Yamaha engine wasn't quite so flexible. If you like to pull a tall gear to aid control and keep the suspension unloaded, the engine feels sleepy. It isn't that the engine is reluctant to pull a tall gear when there is traction, it just doesn't pull at low rpm with a load, a typical situation that a lower-skill-level rider will get into. At one point, there were two tabletop jumps in a row, and screaming in third makes them easy to do. We tried to hit the same jumps at the same speed in fourth gear. Having applied the last-second throttle twist, we waited for the engine to come alive, but it never responded with acceleration, causing short landings for a less skilled rider on both jumps.
If you actually use all of the gears in the five-speed, you will like this motor. Many corners you would take in third on other 450s could be exited in second on the YZ. It is far from slow, and it storms off start lines. It even has plenty of midrange hit (where intermediate-level riders ride) to clear tricky jumps, but you run a little higher in the rpm range than we are used to with 450s. If you want to do the whole track in one or two gears, you may lament the passing of the '06-spec engine.
Despite the time needed to get used to the power, we're calling the '07 YZ450F a success, but we can't wait to get it in a shootout situation. Yamaha has chosen a different route to a competitive 450, and we're curious how it stacks up head to head.