Yamaha may not raise the stakes in the 250cc motocross/supercross class with their 2010 YZ250F model, but the bike does come with a new, more compact "Bilateral Beam" frame and KYB suspension that allow the rider to control it easier. Also, the engine now features modified valves, is being fed through an upgraded carburetor and breaths through a revised exhaust with “D” shaped exhaust port. All the modifications translate into more low-to-mid rpm power, which is precisely what the rider needs during motocross races. We have put together an article based on Yamaha’s press release, so hit the jump to read it.
Ask any motocross rider where races are won and lost and odds on he’ll tell you its all in the corners. A light, nimble and supreme handling MX bike can pick its lines and stick to them, enabling its rider to hang on longer and go harder.
So it’s no surprise to learn that cornering performance was the guiding theme throughout the development of the new model YZ250F.
The next generation motocross development plan was hatched with rider involvement paramount. Trackside customer research led Yamaha engineers to discover that what riders wanted more than anything else was sharp handling. Riders of all abilities from pros right down to swappers. And by handling, they meant better cornering performance. Because a better handling bike lets a rider get on the gas sooner, is less tiring to ride and is the key to winning motocross races.
The development team’s goal was to make quick cornering easy for riders of all skill levels. Not a simple task and certainly not something that could be achieved with small tweaks to the chassis or engine. The goal could only be reached by applying a highly innovative and synergistic approach to the science of motorcycle cornering.
2010 Yamaha YZ250F
The engineers were well aware that the 250 is not just a smaller displacement version of the 450, but a unique machine in its own right. So the task was to design a stand alone 250, not a scaled down 450cc MX bike.
By making a specific 250cc machine, the chassis can be tailored to deliver the handling response suitable for the class. The engine character of the 250 can then be tuned to suit that chassis. And by starting from a clean sheet of paper, not only was the goal of enhanced cornering performance met, the machine’s overall performance was dramatically improved.
The new YZ250F is compact, lightweight and requires little input for rider balance. Which means it’s less tiring to ride. The credit for this goes to the all new Bilateral Beam aluminum frame which features high lateral and torsional rigidity and offers a stable feel and precise handling.
The new frame converts sideways shocks smoothly to longitudinal shocks that are more readily absorbable by suspension. This makes the YZ250F very stable when cornering, which means it’s easier to dive into corners with more speed.
By quantifying rider feedback, the chassis’ rigidity could be more precisely matched to the rider. Additionally, the new frame layout made it possible to change the shape of the fuel tank. By moving the tank towards the centre of the bike, mass centralization was significantly advanced. Further improvements were made by moving the radiator rearward and mounting it lower.
Improvement to the initial damping quality of the front and rear suspension units have resulted in improved traction and give the rider a better feel for the terrain. This allows more confidence when entering a turn and lets the rider hold a line with less effort. The result is less rider fatigue during a long moto.
2010 Yamaha YZ250F
After thorough research and testing, Yamaha engineers decided to retain Yamaha’s five titanium valve engine layout and FCR carburetor fuel delivery system. This combination was found to produce the best power output for the displacement while maintaining compact engine dimensions and light weight.
But the engine has been thoroughly refined for 2010 to result in even more punch. A higher lift intake camshaft, revised exhaust port and carb intake funnel shapes, new valve springs and retainers, smaller oil tank and revised ignition map for the CDI are just some of the many detail improvements that have been made to the 250cc powerplant. The new frame also allowed a reshaping of the air cleaner box which improves intake efficiency.
The result is a more rider-friendly engine with more linear power delivery. Low- and mid-range power characteristics and response are improved, giving the bike a lighter feel when cornering.
The changes were made possible in part by a measurement device used in MotoGP. This device allowed the engineers to quantify the transitional power characteristics when the rider begins to open the throttle after corner entry (1/4 - 1/2 throttle opening). Based on this data the engineers tuned the engine’s response characteristics to give the engine an ideal power feeling for the rider.
Another small but important change was to modify the clutch lever ratio so as to reduce the effort required at the lever. This makes it much easier for the rider to slip the clutch.
As you can see, Yamaha can really brag about the true qualities of their YZ250F, but the fact is that although the 2010 model stands for progress, it doesn’t feature fuel injection such as the 2010 Honda CRF250R does. And Big Red’s motorcycle starts at $7,199, allowing it to stand out as an even more suitable “best bang for the buck” candidate in the quarter-liter class. Suzuki is far from losing ground in this field as their 2010 RM-Z250 is the first 250cc dirt bike to be powered by a fuel injected engine.
Together with the Yamaha bike in case, the 2010 Kawasaki KX250F evens up the scale as this still relies on a carburetion and a hot start circuit to get the job done for the still competitive engine.
2010 Yamaha YZ250F
The YZ250F’s straight frame-work directly expresses the lightweight feel and look a 250 should have. The plastic parts have been made as small as possible while still retaining their protective functions.
The bike’s lightness is further expressed by emphasizing its linear imagery. The flatness of the tank, seat and rear fender also facilitates rider movement and the relationship between the handlebars, pegs and seat make for a natural and roomy riding position. The dart-like styling allows function to follow form, as the YZ250F’s elegant design contributes to its winning potential.
"If there is one area the motor really made a leap in, it is in the transition from bottom to mid. Most of us felt that in roll-ons or when you let the motor fall off the pipe, the previous YZ250F was a little resistant to get ripping back into the top end. Sort of like you were dragging the brake just a bit. But not the 2010." – dirtrider
"Grunt out of corners is the best improvement, but honestly the entire powerband is more effective and fun. The Yamaha used to scream its lungs out but not really generate any over-rev power, but that’s changed this year with additional pull on top. Whether torquing around or revving the beans out of the 13.5:1 compression engine, the exhaust note is pleasant." – motorcycle-usa
"The crux of Yamaha’s 2010 YZ250F is essentially a new, “bilateral” aluminium beam frame designed specifically for the 250, rather than being the common part for 450 too. New caster and trail dimensions have made steering more positive too." – superbike
"It’s lean, mean, and minimalistic. The flatter seat is easier to move around on, and they did a lot of work to centralize the weight…moving the radiators rearward and lower, and narrowing the tank. That definitely makes it easier to move around on. The ride position is a little further forward than in the past, and there are provisions to allow you to move the bars forward or back over a 30mm range." – vitalmax
"The bike feels light, slim and aggressive to ride. Coupled with its aggressive powerband, the YZ250F inspires riders to go faster. That light feel helps it work in the woods as well, and backing off the compression on the fork seven or eight clicks lets it work acceptably off-road for all of you one-bike-does-it-all riders." – motorcycle
“It also had no problem in absorbing the bigger jumps, especially the big step up which I was purposely trying to over jump to see how the suspension would cope with some bigger forces. Even though the “rollers” or stutters as I call them with a stutter gumby at the helm, the bike was able to soak up and stay controlled to a point that I feel like I was actually half in control.” – mcnews
When thinking at which of the four Japanese 250cc motocross bikes to buy, the price will certainly have no significant influence because they all start at $7,000 +/- 100 bucks depending on the manufacturer. In the case of this Yamaha, we’re talking about a $6,990 MSRP for the Team Yamaha Blue/White colored bike and a $7,090 one for the White/Red, 2010’s special color scheme.
While launching an all-new, YZ450F model best characterized by innovative construction methods, Yamaha decided that their YZ250F model can maintain its place among the favorites of the class with only a significant range of improvements, but still no fuel injection system to brag about. What if they launch the reverse-cylinder YZ250F next year? Now that would be something else!
The all-new, Bilateral Beam frame is specific to the 250 and is more compact than the previous generation chassis. This places the rider closer to the front wheel, which delivers superb rigidity balance for unmatched lightweight handling and cornering. This nimbleness lets the rider get on the gas sooner out of corners and cross the finish line with less fatigue – even on long motos.
The optimized engine delivers a new level of power in low-to-midrange, with a great torquey feel, exactly where riders want it. That is due to the new straight intake boot that enhances breathing, new carburetor that provides excellent throttle response and fuel atomization, and redesigned valve train components that reduce inertial mass and boost low end torque. Exhaust is also enhanced with a new D-shaped exhaust port and newly designed exhaust system. Ongoing refinement to the suspension and engine produces an amazingly balanced, light-handling machine with performance that’s accessible to all levels of riders.
All new styling emphasizes the bike’s light weight and nimble handling character. The sharp, horizontal lines set the bike apart, with a clean, aggressive look.
KYB® suspension has been recalibrated front and rear and is tuned to work with the new Bilateral Beam frame for unmatched handling. The clutch lever has a lighter pull feel even though the clutch has stronger engagement. The new clutch also has a wider engagement range that will give riders an advantage off the line. . . shift after shift, moto after moto.
There’s no disputing the YZ250F’s unmatched four-stroke prowess – it was the 1st four-stroke 250 motocross bike on the market, the 1st to win an international race, the 1st to win an AMA® Supercross ® and the 1st to take an AMA® U.S. Supercross Championship® title, as well as the first to win an AMA® National race.
The valve spring retainers are now lightweight aluminum instead of steel, and valve spring pressure is lighter for reduced valve opening force. This contributes to superior low-to-mid range torque characteristics due to less power-robbing friction. There’s also a new, higher lift cam profile, while valve stem ends are chromium-nitride coated for exceptional reliability and reduced maintenance.
The exhaust port shape has a “D” shape instead of round. This increases velocity through the port for excellent throttle response, while enhancing the power feeling of the engine.
The newly designed radiator is lower and further back and the oil tank is more compact and repositioned to achieve greater mass centralization.
The carburetor bore has a new venturi shape, plus there’s recalibrated jetting and a new accelerator pump. This translates to impressive response when the rider snaps open the throttle, and contributes to superb torquey low-to-midrange power characteristics.
The intake boot offers a straight, smooth tract for excellent engine breathing and more power. The airbox is reshaped to tuck neatly into the Bilateral Beam frame.
The exhaust pipe has been carefully tuned to optimize engine power, with a muffler that’s 50mm longer and with a narrower core – a design that lets the YZ250F comfortably meet the latest noise standards without sacrificing power.
Engineers were able to increase the clutch spring load for stronger engagement, yet, thanks to a recalibrated clutch actuation arm cam ratio, lever pull is actually lighter than before.
Third and fourth gear ratios are slightly taller, and third, fourth, and fifth gears are stronger than ever with new drive dog shapes for positive engagement. That gives riders a strong gearbox that’s been carefully matched to engine power characteristics.
The Bilateral Beam frame is crafted from a carefully chosen combination of forged and extruded aluminum pieces – 20 in all – all welded together to provide unmatched rigidity balance.
The KYB® speed-sensitive front fork delivers exceptional damping feel, responsiveness, and bump absorption characteristics. Damping settings are revised, the piston rods have a new surface treatment, and the oil seal is a new design.
The 4-way-adjustable KYB® rear shock has been redesigned to make the most of the Bilateral Beam frame design. It’s lower in the frame for excellent mass centralization, and has new damping characteristics.
The new tank, seat, and rear fender are flat and the relationship between handlebars, pegs, and seat result in a natural, more forward riding position that facilitates rider movement. The fuel tank has been moved toward the center of the bike for mass centralization. The ProTaper® bars are four-way adjustable, and handlebar mounts and footpegs are 5mm higher to optimize rider position on the new chassis.
The CDI unit has revised ignition mapping to match new engine intake and exhaust specs.