Inside The 2010 Yamaha YZ450F 12

Broc Tickle flicks the new 2010 Yamaha YZ450F over a jump at Budds Creek. Click any image for a larger version.

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When we first spotted an early leaked photo of the new YZ450 in the Vital MX Forums, we wondered if it was the real deal, or just a Photoshop prank. Yep, it had the look of one of Yamaha’s Powerpoint presentations (which are normally under very strict embargo dates for release), but there were so many changes to the bike, you had to wonder if it were real or not. Fuel injection? That wasn’t unexpected, given that they’d be the last Japanese 450 to make the switch. But switching the location of the intake and exhaust? That made for some flashbacks to the days of Cannondale’s ill-fated effort into the motorcycle scene.

Yamaha dialed us in with a white version of the newest YZ450F, which comes with black wheels. European editions of the bike feature black wheels on the blue model as well.

Of course, we got the real conformation just after Steel City, when Yamaha did their press reveal of the new bike. Shortly after that we also received an invitation to come out and check out the new bike at Budds Creek, and how could we say no at a chance to ride one of the first 17 bikes in the U.S? (And four of those belong to Yamaha’s Racing Department.) We were really looking forward to this one.

Just a switch to fuel injection would be a large change, and so would an all-new engine design like this bike features. But this bike goes well beyond that, with a 180-degree change to the intake and exhaust positions, and a tight integration with development of a new chassis, and more. Let’s dig in.

Engine

One of the big design goals on this bike was making it easier to ride, and one of the ways that they set out to achieve it was by centralizing the weight as much as possible. One way they set about doing this was rotating the cylinder back nearly 13 degrees from the incline of the '09 models. But this also provided the dual benefit of making for a very straight flow of air for the intake and exhaust on the new engine design.

We like the simple look of the new powerplant. You can see how it has a lower height than in the past, is rotated back in the frame, and has a reversed intake and exhaust.

Yamaha also tweaked the position of the cylinder on the cases, moving it 12mm forward of the crank center. Their goals here was to make the connecting rod more vertical at the moment of greatest combustion force, but it also provides for less piston friction. Yamaha claims this provides a more efficient use of the available power, and improves throttle-to-rear-wheel feeling…more of a direct connection.

Power? Yep, the new 450 has plenty of it. It's easy to control, and no, it's not slow.

They also went with a bigger bore and shorter stroke on the new engine, with a half-millimeter shorter crank, and a two-millimeter larger bore. That allowed them to reduce the height of the cylinder by 15mm, and reducing the overall height of the engine.

They made quite a few changes to the piston as well, bumping compression up a smidge, from 12.3:1 to 12.5:1, and eliminating the piston pin offset that the ’09 model uses. The piston ring shape and tension has also changed. A notch was added to the second ring for more effective oil scraping, and the tension of the rings has been reduced by approximately 40%.

After years of using a five-valve design, the new engine has a four titanium valve arrangement that better matches the fuel injection. The cam profiles have changed, and they’ve also gone from a round valve spring material to an oval shape to make shorter springs possible without coil bind.

The fuel injection unit on the new YZ450F includes a 44mm Keihin throttle body with a 12-hole injector, and like the other fuel injection systems we've seen in use for motocross it's a battery-less system that stores a charge in a condenser as soon as the bike is kicked over, and that powers the tank-mounted fuel pump. The fuel injection ECU monitors the usual functions, including throttle position, intake pressure, atmospheric pressure, coolant temperature, air temperature, and crank pressure, but they've also added a G-sensor that will automatically shut off the bike if it's laid over for more than ten seconds.

Here's a view of the new GYTR Power Tuner. Nope, no laptop required.

Yamaha also has an optional GYTR Power Tuner ($279) that lets you plug in at the track and adjust fuel and ignition maps to match your track and riding conditions, as well as any engine mods you may make. The cool part is, it’s a standalone unit powered by two AA batteries. There are no laptop or external batteries required. It’ll store up to eight maps, it has some diagnostic features built in, and you can even use it while on the way to the track. It doesn’t need to be plugged into the bike.

Okay, so now you’ve got the basics on the engine, but how about the reversed layout? One of our favorite parts of the new bike's layout is the air intake and airbox. Starting at the front, the shrouds now curve around much further on their leading edge than before. This gives you two benefits. First, it provides substantial protection against any roost entering the air intake, and it also guarantees that your outstretched boot will never hook up on the shrouds again while you're laid over in a turn.

Want a look under the hood? You can see how easy it is to access the air filter on the new YZ when you flip up the fuel tank, which now resides under the flattened seat. There's a built-in heat shield for the fuel tank.

Air filter maintenance is also dead simple. Remove two bolts for the seat. Two easily accessible bolts for the shrouds/fuel tank are next, and then two bolts at the top of the airbox cover. You simply tilt the tank upwards, using a cable that Yamaha provides in the bike's tool kit. One end loops around the subframe, and the other hooks to the front seat mount on the tank itself. Remove the airbox cover, unhook the bar that holds down the filter cage, and remove the filter. The filter itself has also been simplified, since it's a single flat piece of foam, rather than built up from multiple pieces that are glued together. No more worrying about filters coming apart during cleaning.

One thing you will notice while riding the bike is that you do hear a bit more of the throaty air intake note as it gobbles up oxygen in a hurry.

You can see how open the area under the seat is, now that the airbox has been moved to the front. The tornado-style exhaust is even longer than in the past, which adds to the low end power.

On the opposite end, there’s the “tornado-style” exhaust with a built-in resonance chamber. To achieve good low and mid-range power, you need an exhaust with enough length to it…which is why we’ve seen some very long pipes exiting the front of the engine in recent years. With this design, it’s actually longer than the ’09 pipe. But now that there’s so much extra room under the seat because the airbox is at the front of the bike, you not only don’t have to worry about crushing the pipe in contact with another rider, the bike can also make use of larger and lower radiators that fill the spot where the pipe uses to exit the engine. There’s also plenty of room around the shock (and enough ventilation from the exposed bodywork) to keep the area cool. In addition, there’s thermal material on the inside of the sideplates, and a metal heat shield under the seat. We set our hand atop the seat of a bike that had been sitting idling, and could feel no heat through the seat.

Chassis

Since they were starting with a blank sheet of paper for this bike, Yamaha’s designers wanted to closely integrate the chassis and engine. Taisuke Sakurai is the team leader and focused on engine development, while Shidehiko Miyashiro was the head of chassis development. They were on hand to answer questions on the bike’s development, but were just as interested in getting feedback from the riders on hand at the test. They were apparently quite happy to get the same type of feedback from the assembled media that they’d received from their test riders.

Shidehiko Miyashiro (left) was the head of chassis development on this bike, while Taisuke Sakurai Iright) was the team leader and focused on engine development. These guys were like proud parents, and very keen to get feedback from the media and test riders.

By switching from a single backbone to a bilateral beam design (like we first saw on Yamaha’s YZ250F earlier this year), it gave them room for the airbox configuration they wanted, but they also were able to get the frame flex characteristics that they were looking for. The aluminum frame is constructed with a blend of cast, forged, and extruded components. The extruded twin bilateral beams are hydro-formed, which allows Yamaha to achieve the unique double S-bend shape they wanted, while maintaining maximum strength. If you look at these pieces from the side, and from the top, they form an S-bend in each direction.

During conversations with Sakurai and Miyashiro, they discussed how difficult the frame was to build, and that the prototype cost of each one was close to the cost of, “One large car.” Apparently they went through quite a few of those during testing.

So in the puzzle of where to locate everything on the bike, where did the fuel tank move? It moves rearward, under the seat, and almost directly over the engine. But an advantage to the new design is that there’s a built-in heat shield under the tank, which should do a much better job of keeping the heat away from it than in the past. It’s also molded from a semi-transparent gray plastic that helps you spot the fuel level. It is a bit tricky seeing just how full it is, since the bulk of the fuel resides in a lower section of the tank, while the extension at the front (under the gas cap) is rather slim. Yamaha claims that by moving the fuel weight to the center of the bike, it reduces differences in the bike’s handling as the fuel level changes.

Broc Tickle was having a blast riding the bike. Enough so that he ran through a tank of fuel on one of his motos, and left some dried blood on the throttle grip where he worked a hole in his thumb. He didn't want to get off the bike.

By moving the fuel tank, they were also able to design a flatter seat, which is easier to move around on. Though the fuel tank is smaller in capacity (1.6 gallons vs. last year’s 1.85 gallons), there will be less fuel loss via the float bowl vent tube over the length of a moto. We do wonder how heavy-handed riders who use this for really long motos and off-roaders will boost the capacity of their tanks, but our guest tester for the weekend, Broc Tickle, rode for probably an hour on a tank of fuel.

As far as suspension, the new layout of the components and the new frame allowed them to do some different things in the rear end as well. The shock is now center-mounted on the frame rather than having to be nudged to one side for the intake. The flex characteristics of the swingarm were also changed to match the new chassis. The KYB rear shock also has a horizontally oriented piggyback reservoir that’s larger than before, and the shock body now uses a 50mm piston, rather than 46mm.

Up front, you get a KYB speed sensitive fork with 310mm of travel (up 10mm from last year). Details on the fork include a new oil seal, new inner rod surface treatment, and like the shock, about a 10% boost in low-speed damping. As far as triple clamp offset? It’s been reduced from 25mm to 22mm.

What’s left from the ’09 model? Wheels, and goodies like the Pro Taper bars and the controls. That’s it.

On Board

Visually, the bike is very striking. Like we noticed with the 250F introduced earlier this summer, we think it looks better in person than in photos, but one thing is for sure…there’s little chance that you’ll confuse this with anything else on the gate. It’s a very aggressive and minimalist styling, and they really emphasized the open area where the exhaust and shock now reside (we’d guess partly for the cooling abilities). But it also makes it visually lighter.

We love concept art of bikes like this. It gives you some insight into what the designers had in mind during earlier stages of the bike. As you can see, the finished project isn't far off from their original vision.

Settling in on the bike, you don’t really notice anything different. The width of the shrouds are similar, and the bike is very slender through the middle. When you’re on the gas, you do hear some added intake noise that you don’t normally get, but that’s not unexpected, with the intake that close to you. We’ve seen some photo in the Vital MX Forum of James Stewart’s new bike, where they’ve added some machining on the shrouds to add slots for extra air. Of course, if you want to go scary-fast, Yamaha already has a full line of GYTR hop-up components in place for the new machine, including cams, piston, head, pipe, and more. And that’s in addition to being able to tune via the fuel and ignition maps.

Broc Tickle has spent the last three years aboard 250Fs, though he did ride his first three nationals on a 450, and he was impressed with both the power and controllability.

Light feeling and flickable?Yep, you could say that. He was having fun.

Yamaha has been testing with fuel injection for several years on motocross bikes, though often when it was used at public races in Japan, it was hidden by a carbon guard, so prying eyes (and cameras) couldn’t tell if the bike was equipped with a carb or a fuel injection throttle body. There’s no big difference in performance, other than no cough or bog when cracking the throttle open. We did run into a couple stalls in odd spots, but usually at very low RPMs.

For us, the biggest difference is in cornering, and the way it feels over bumps. As Taisuke Sakurai told us, “You guys understand that many heavy parts, far from the center of gravity feels very heavy. But concentrate them closer to the center of gravity, and it feels lighter.” One of their primary goals on this bike was to make it quick and nimble. “Light handling” was something emphasized over and over in their press materials. Small bumps and bigger braking bumps? They didn’t seem to affect the bike quite as much as we’d have expected on a more traditional layout.

Initially, Broc thought the front end was too soft, and the Yamaha guys remedied that by adding 10mm to the oil height, and doing a bit of tuning on both the front and rear ends. Of course, Broc’s used to riding modified suspension, and rides hard, so it’s not too surprising that he was looking for something just a bit stiffer.

Broc rails an off-camber berm.

Cornering was also rock-solid, whether you were digging for an inside line, or railing around a berm. If we sound impressed, it’s because we are. They really seem to have hit their marks with this bike.

Wrapping Up

The concept of this bike was started almost three years ago, with much of the original concept coming from an internal (and often after-hours) group within Yamaha called the YZ Research Team that included members from both the U.S. and Japanese headquarters; and members of the product planning, testing, engineering, PR, and design teams.

Interestingly, it apparently took a while for the top management at Yamaha to accept this idea because it was so different. But after lots of work and pushing from the designers, it was accepted, and they moved forward with it.

Thanks to Yamaha, and to Broc Tickle for the help at wringing out the new bike. Be sure to check out the link to the video above for more from Broc.

On this bike, Yamaha wanted to produce something as revolutionary as their original ’98 YZ400. We’d say that they easily accomplished that goal. For every question you have about it, they’ve got a solid reason why they made their design choices, and a lot of it just plain makes sense. This could very well be one of those bikes that changes the way motocross bikes look in the future.

2010 Yamaha YZ450F Specs
Engine Type: 449cc liquid-cooled DOHC 4-stroke; 4 titanium valves

Bore x Stroke: 97.0 x 60.8mm

Compression Ratio: 12.5:1

Fuel Delivery: Yamaha Fuel Injection (YFI), Keihin® 44mm

Ignition: CDI

Transmission: Constant-mesh 5-speed; multiplate wet clutch

Suspension/Front: KYB® Speed-Sensitive System, inverted fork: fully adjustable, 12.2-in travel

Suspension/Rear: KYB® Fully adjustable single shock; 12.4-in travel

Brake/Front: Hydraulic single disc brake, 250mm

Brake/Rear: Hydraulic single disc brake, 245mm

Tire/Front: 80/100-21-Dunlop® D-742FA

Tire/Rear: 120/80-19-Dunlop® D-756

L x W x H: 86.3 x 32.4 x 51.6 in

Seat Height: 39.3 in

Wheelbase: 58.7 in

Ground Clearance: 15.0 in

Fuel Capacity: 1.6 gal

**Wet Weight: 245 lb

Color: Blue/White ($7,990); White/Red ($8,090)