When you think of 250cc four-stroke motocross bikes, Yamaha’s YZ250F has been a leader in the category since its introduction back in the year 2000 – a model which I myself just had to have despite racing for the factory Honda road race team at that time.

It was new and innovative, accelerating four-stroke development in the Lites class of motocross, but since that time the models across the board have continued to improve and for 2010 Yamaha has stepped it up even further once again after the bike has received numerous developments over the years.

For 2010 Yamaha has focussed on the chassis without ignoring its already competitive engine, although it retains a carburettor rather than switching to fuel injection as both Suzuki and Honda have announced for next year’s models.

The chassis is largely revised and redeveloped with a Bilateral Beam aluminium frame, developed to increase front-end feel and to improve the steering while maintaining the exceptional stability that Yamaha has become known for.

As mentioned, the engine isn’t all-new, but it does have many crucial developments that are all designed to boost to bottom-end and mid-range power while making it accelerate as smooth as possible – one of the reasons why Yamaha has stuck with the carbs thanks to its lengthy experience in the technology.

Styling is possibly the most striking new change that goes hand-in-hand with the chassis, and whether you like it or not, they say that change is as good as a holiday and Yamaha may just have found the ultimate way to spike interest in the new model by drastically revising its look.

Some have likened it to a Husqvarna, but in my eyes it’s fresh, new, and will definitely stand out as a shiny new 2010 model bike when you roll it out at your local track.

One thing to realise is that while it was a shock to look at in the first release of press images, it looks unreal in the flesh with its sharp lines and added texture designs in certain parts of the plastic (mostly on the airbox covers and shrouds) for added grip, definitely signifying its changes beneath the plastics.

So with the base changes noted here and the detailed changes listed in the tech info below, how does the new model translate to the track? Put simply, Yamaha’s on to a winner with this one – a bike that may just entice riders to ignore the lack of EFI and soak up the benefits of its entire package.

After a day of testing at the Australian launch in Cessnock, NSW, just days after the penultimate round of the Australian MX Nationals at Lakes in the next town over, it seemed as though every moto-journo on hand was excited with Yamaha’s new creation.

Starting when either cold or hot is simple enough with a quick pull of the hot-start lever doing the trick if you stall or crash (I can attest to this one) while midway through a moto or even a race. If it doesn’t fire up first kick, there’s a good bet it’ll fire on the second.

The super light clutch feel is instantly noticeable when first clicking into gear, and even more noticeable once on the track when you engage the clutch into the turns and then especially when you ride it off the tighter turns to add a few hundred rpm.

Also instantly noticeable is the revised ergonomics set-up, with a taller feeling upon take-off and the flatter seat enables you to get over the front of the bike a little better – increasing the relationship between rider and bike in corner just as Yamaha planned.

In summarising the ergos, it’s taller, feels narrower than previous models, and rejuvenates the bike in a way that makes it feel more modern in its stance and begs for an aggressive riding position.

While the seat height is higher than the 2009 model, the new bike is more flickable in the turns on change of direction, and once you’re finished braking and set up for the corner, the front-end makes it easier than in the past to place it in a rut while committing to your line.

This comes down to the revised dimensions of the rake, trail, and even the shorter wheelbase that has helped to improve the bike’s low speed handling.

There is a lack of ruts at Cessnock but enough to get a basic idea for the launch, and its feel on the flat, hard, blue groove surface of the track is also quite good considering how slick it can get.

Speaking of the brakes, they are touchy at both front and rear, although they are adjustable ad produce plenty of bite in the way they are applied. They take a little to get used to because they are strong, but we also need to remember that the bikes were almost brand new heading into the launch.

Stability is good at speed when set up right, only bouncing off the square-edged bumps on the hard-packed sections of Cessnock before I had the guys at Yamaha Australia set the sag and soften up the suspension for me.

Those changes made the suspension compliant as the track continuously got rougher as it got dry and dusty in the afternoon, making me a lot more confident when on the gas on some of the longer straights.

In fact, while the bike’s more than suitable for a wide variety of riders, the 2010 YZ250F responds better and better as you learn to push it harder, and I’d say that the bike would work even better on softer soil where you could rail the turns faster.

The four-way adjustable Pro Taper handlebars are perfect to suit either tall or short riders, with the furthest setting back the best option for my 168cm height. Rolling the ’bars back a bit also assisted in stability without upsetting the turning for me.

Engine power is very much linear off the bottom, with the fuelling producing a smooth application with no clear bog noticeable by me at all throughout the day, but the linear power is not the absolute standout of the engine.

The standout is the fact that the power is noticeably increased off the bottom, with the revised gear ratios for third and fourth gear assisting in allowing the engine to keep on pulling hard with just a quick slip off the clutch.

It not only feels more powerful in the low and mid-ranges of the powerband, but also pulls for longer in the bottom gears with a good amount of over-rev allowing you to hold gears for a touch longer – a nice bonus on a tight track like Cessnock.

Those mentioned revised gear ratios are especially handy in third gear, making it easier to pull in third gear off of mid-speed turns while relying on the added engine power without lagging it as much as in previous years. It’s basically making life easier than ever before for a 250F rider, and the chassis compliments it perfectly.

Serco Yamaha factory rider Mitch Hoad was also on hand for the test and said that he’d even ridden it on Supercross for a short time, mentioning that the increased bottom-end power works well on Supercross too, even for a stock bike.

Next year’s models in the Lites class are going to be a great step ahead of this year, with Yamaha already getting the jump on its competition by being the first to launch its model for twenty-ten already.

If there’s one thing you can be certain about with the brand new YZ250F, it’s that Yamaha has easily met its design brief, ticking all the boxes it set out to in improving its steering, power and even its styling.

We’re pumped on it, so we’ll have to see what the other manufacturers can bring to the table if they want to match it.

TECHNICAL INFORMATION:

CHASSIS
Yamaha has focused on improving the handling of its all-new 2010 model YZ250F, with the chassis undergoing many detailed changes in the aim of improving turning prowess while maintaining stability at speed.

The new-design aluminium Bilateral Beam frame has been adopted in order to assist in the centralisation of machine mass, and is made up of approximately 20 parts of forged, extruded and panel aluminium parts welded together into a single frame.

With centralisation in mind, the chassis is much more compact than on previous models, which is designed to increase feel between the rider and the bike. In terms of rigidity balance, the lateral rigidity and torsional rigidity have been increased compared to the 2009 model.

The dimensions of the new chassis are also much changed. The wheelbase is shorter (1476mm to 1473mm), caster angle relaxed (27.1 degrees to 27.4 degrees) and trail longer (117.4mm to 119.6mm).

Meanwhile, the headstock is 12mm lower and the handlebars are higher (39mm to 44mm), retaining the four-step adjustable handlebar position that was also on the ’09. The ground clearance is increased (371mm to 376mm).

Suspension on the new model has been widely changed, with the valve damping has been optimised and a new spec of the inner rod has been used. These changes are what contribute to the front-end grip in turns at both high and low speed. The shape of the outer tubes has also been changed to balance the rigidity with the new frame.

As for the rear suspension, the 2010 model adopts the same basic rear suspension spec as the existing model, although the position of the spring of the suspension unit has been lowered 29mm. The swingarm is the same type as on this year’s model.

Rider ergonomics have vastly been changed due to a new flat-style seat that’s been specially developed for the 250F, also made a little stiffer at the bottom for greater comfort while retaining the same material.

The flatness of the tank, seat and rear fender also facilitates rider movement, and the relationship between the handlebars, foot pegs and seat make for a natural and roomy riding position.

The plastic resin fuel tank is designed to achieve the best relationship with the new frame and new dimensions, with the centre of the tank moved closer to the rider to contribute to better centralisation of machine mass and a greater sense of compactness for the rider.

Apart from that, the thickness of the radiator core has been increased and the mount changed from a two-point to a three-point mount, thus achieving better heat-dissipation performance and greater unit reliability at the same time.

Weight has been slightly decreased from 102.8 kilograms to 102.0 kilos with newly designed lightweight parts including the sprocket, a plastic resin engine protector (skid plate), more compact oil tank, optimised brake pedal shape and smaller brake hose guides.

The styling of the bike looks much different and also attributes to the light weight, including new shapes for the front fender, rear fender, front number plate, front fork protector, side covers and air scoop.

Also, the plastics have new textured parts in places, not only for added grip, but they are also intended to keep the bike looking good even if there are scratches etc on the plastic according to Yamaha.

Once again the model comes in both the traditional blue and secondary white colour, offering Yamaha fans that added option when deciding what bike they’d like to purchase.

ENGINE
While the focus has mostly gone into the chassis on the 2010 model YZ250F, Yamaha hasn’t ignored the engine by any means, with a greatly improved package that has increased the power throughout the range by making it more linear and stronger in the low and mid-range power.

Yamaha engineers decided to retain Yamaha’s five titanium valve engine layout and FCR carburettor fuel delivery system, surprisingly choosing to stay with the carbs instead of adopting fuel injection for the new year.

According to the press kit, this combination was found to produce the best power output for the displacement while maintaining compact engine dimensions and light weight as an overall package.

But the 250cc, liquid-cooled, four-stroke, DOHC, single-cylinder engine has been thoroughly refined for 2010 to result in even more punch.

While it retains the 77.0 x 53.6mm bore and stroke as the 2009 model, as well as the 13.5:1 compression ration, engineers have used optimised intake/exhaust systems, lightened valve assemblies, revised carburettor settings and new ignition advance characteristics. In particular, the measures to reduce power loss in the valve drive mechanism have given this engine a new character.

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 powerplant. The new frame also allowed a reshaping of the air cleaner box to improve intake efficiency.

The changes to make it more linear were made possible in part by a measurement device used in MotoGP, which allowed the engineers to quantify the transitional power characteristics when the throttle is opened from quarter to half turn.

In detail, to improve smoothness through the rpm range, the retainer that holds the intake/exhaust valves has been changed to an aluminium unit (steel on the existing model) to reduce inertial mass in the valve drive mechanisms. In addition, the spring rate of the valve springs has been reduced to balance the reduced inertial mass.

Adoption of this new valve spring reduces the amount of force necessary to open the valves, which minimises power loss and thus contributes to superior torque characteristics in the low- to mid-speed ranges.

As noted above, the settings of the FCR-MX37 carburettor have been refined to accommodate the changes in the intake/exhaust systems. Also, the spec of the cam for the acceleration pump and the shape of the air passage on the air cleaner side have been changed.

In order to achieve the target performance, the shape of the exhaust port has been changed from a round cross-section to a “D” cross-section to contribute to the new engine character.

Australian spec models come with lightweight silencers, with the length of the outer tube shortened by 55mm and the tail pipe shortened by 40mm. Also, in response to the new frame, the silencer mount has been changed to a rigid type that reduces weight.

Another vital change in the in the engine is that the gear ratios for third and fourth gears have been changed, third was 1.450 and now 1.444 while fourth was 1.227 and now 1.222, also attributing to the added punch off the turns where you can hold the gears for longer.

Another small change within the engine is that the clutch spring load has been changed, with the length of the push lever cam also modified to change the lever ratio and reduce operational load.

Function has been improved with slight changes such as the crankcase cover being given an oil level gauge window, while the drain bolt position has been changed for easier servicing – all adding to the overall value of the motorcycle.

CLICK HERE FOR OUR VIDEO OF THE 2010 YAMAHA YZ250F LAUNCH