2010 Yamaha YZ450F - Road Test

For 2010, Yamaha’s YZ450F gets a new motor and a redesigned chassis.

2010 Yamaha YZ450F - Road Test

2010 Yamaha YZ450F - Road Test

Time flies. It already has been 12 years since Yamaha reintroduced the four-stroke as a viable motocross bike for reasons as simple as controllable power and improved traction. Who'd have thought this concept would take off with such success that the four-stroke would become the preferred engine for every manufacturer's premier motocross machine.

But breakthrough designs don't come around every year, especially with bikes that have to compete at the highest levels of professional supercross and motocross, yet still be suitable for amateur racers and recreational riders. So it's with considerable risk that Yamaha decided to break with long-standing tradition on the 2010 YZ450Fby mounting the engine's cylinder and head backward. The intake is now at the front, the exhaust at the rear. You can learn all the details about this breakthrough design and the engineering behind it in Kevin Cameron's "Reverse Engineering."

Yamaha's reasoning for this drastic change was to give the new YZ more of the characteristics every MX rider wants—nimble handling, effortless cornering and precise chassis feedback. The bike also must have other important traits, including competitive but controllable power and, in this era of electronic fuel injection, tunable power delivery. That's a big list of demands, but it's the result of feedback from professional racers, amateur racers, weekend warriors, focus groups and Yamaha dealers.

Under the guidance of a new team of engineers, the 450F started as a clean sheet of paper. Its project leader, Taisuke Sakurai, has been with Yamaha for more than 20 years working on bikes such as the FZR1000, GTS1000, V-Star 1100and FJR1300 before making his way to his greatest passion, dirtbikes. There, he has lead the development of the YZ250Fand now this "backward" YZ450F.

Overall, the 450's engine design is based around two concepts: "mass centralization," a term that has been kicking around the industry for many years; and having the straightest possible intake tract for optimum power. This led to a whole host of changes in the design of the rest of the bike, including the frame, the exhaust system and even the location of the gas tank. So, this machine is different in more ways than just a swap of its intake and exhaust.

This includes the switch to batteryless fuel injection, making the new YZ the last of the Japanese 450cc MXers to adopt this technology. But despite all the performance advantages of EFI, this particular system has one drawback: starting. The engine must complete two rotations before firing, and that demands a strict starting procedure: Use the kick lever to move the piston to TDC on the compression stroke, return the lever to the very top of its travel, then kick through. This is a lot easier than it was in previous years when hot-start buttons and decompression levers were required; but if the engine stalls in the heat of competition, following this procedure will be a mental challenge for a lot of riders. When the starting drill was done properly, our test bike fired on the first or second try; when it wasn't, the engine usually failed to start.

Once running, though, the engine has a completely new personality. For the past couple of years, the YZ450F has been on the lazy side compared to the stout shooters from Kawasaki and Honda. But that was not all bad; the YZ's "easy" power was the favorite in our 2008 Vet MX comparison. Those vet riders will have to steady their wrists this year, though, because the new four-valve engine has sharper, harder-hitting low-end and midrange punch. Instead of a gradual flow of power from bottom to top, the YZ now has a more direct, "right now" delivery; and thanks to the injection system, the throttle response is instantaneous. This means power to the ground faster and better, making the bike quicker corner-to-corner, especially when that distance is short.

In our first outing at Budd's Creek Motocross Park in Maryland, track conditions were nearly perfect with plenty of loam and traction-packed dirt. Just once when the track was watered did it get slippery in one spot, and only then was the power slightly overbearing. (In the near future, we will be testing the $280 GYTR fuel-injection tool that lets the rider tune the power to suit the conditions.) Although the downdraft intake is supposed to help top-end power, I found that the YZ lacks some juice up near max revs. That had me shifting through the gears quickly rather than letting the engine pull through its peak power rpm and slightly beyond.

The transmission works flawlessly, though, offering a smooth and positive feel; I never missed a single shift. Clutch pull is typical but engagement is precise, allowing excellent control.

Lots of precision in the chassis, too, which was redesigned around the new engine layout. The main frame is a bilateral beam design that Yamaha has dubbed the Double S Bend because the main beams have an S-shaped curve when viewed from the top and the side. This design is claimed to help better absorb harsh impacts with less spring-back. The frame is symmetrical, and even the KYB shock has its reservoir centered to keep weight on the bike's central axis.

All this "centralization" works as advertised. The bike stays straighter with less of a tendency to swap or get out of line—a trait that comes in handy when you inadvertently jump into a rhythm section sideways and don't land straight. Weight that would previously cause the bike to twitch sideways now helps you snap it back in line faster and easier. The same is true when hitting small chop before a corner entrance; the bike stays in line so the rider can make an accurate corner entry and easily hit the desired line or rut.

So, too, is the bike's cornering impressive. Past Yamaha 450s have been one of the hardest bikes to turn; you had to push, yank and lean on them just to turn as intended. With the new bike, I found myself coming into corners with more speed, yet the bike always instantly responded to my input and locked into the turns. My biggest problem was fighting my occasional bad turning technique rather than fighting the bike.

Even though the new YZ is eager to change direction, it has straight-line handling equal to and possibly better than that of last year's bike. Without having the '09 to try back-to-back, I can't say it is far better. But I can say that the 2010 bike didn't give up any stability to gain its cornering agility, as some bikes tend to do.

Credit some of that to equal front-to-back balance. Another contribution of centralized mass, yes, but it helps to have excellent suspension. The 450's new KYB fork has a 10mm longer stroke and 10 percent more low-speed compression damping. A new damper-rod surface treatment smoothes fork action for better comfort and compliance. The KYB shock is all-new and has a 50mm piston rather than the previous bike's 46mm unit. And like the fork, low-speed compression damping has been increased 10 percent.

Thanks to these new pieces, the 450's small-bump absorption is second to none. Charging over braking bumps is easily doable—the bike stays straight and doesn't jackhammer into the corner. The suspension also is well-balanced for jumps, whether it's a small seat-bouncer or a third-gear wide-open double. I felt no harsh bottoming while landing the latter, even when slightly over-jumping and casing.

As nimble and light-feeling as the new YZ450F is, though, the weight isn't gone; in fact, the bike is heavier than before. This is only an issue when hitting a greasy mud section or trying to yank the bike in a different direction mid-air.

So, a potent new motor and a redesigned chassis blend to make a more balanced bike that accelerates harder, turns better and has more stability. Without comparing the YZ450F head-to-head with the class hot shoes, I can't say it's the best yet; but based on my first rides, Yamaha's backward engine design may just help put the 2010 YZ-F at the forefront of the 450 class.

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