2008 Yamaha WR250R
The beginning of an exciting new era
Ten years ago Yamaha surprised the motocross world with the launch of the world’s first lightweight and compact 4-stroke off-road race bike. Within a very short period of time the innovative new Yamaha 4-stroke was winning at the very highest level in Motocross Grand Prix and US Supercross.
Since then, Yamaha has established itself as the most dominant force in the development of high-performance single-cylinder 4-stroke off road race bikes, winning world titles in every major motocross and enduro category. Now, for the first time, our advanced World Championship-winning technology is being offered to the thrill-seeking street rider who is searching for the ultimate experience in cutting-edge 250cc single-cylinder performance.
Having identified the potential demand for 250cc in the enduro segment Yamaha set out to create this new high-specification 250cc model, which would not only deliver class-leading engine and chassis performance, but would also feature some of the most advanced technology seen in the class.
Our designers are pleased to announce the introduction of the WR250R on-off road model, and the WR250X supermoto. Powered by high-performance race-developed engines housed in lightweight aluminium chassis designs, these two new 250cc single-cylinder lightweights add a new dimension to the world of motorcycling, and offer performance-minded riders the chance to experience bold, new and exciting models that dare to be different!
The WR250R and WR250X have been developed with the same overall philosophy that characterises the class-leading YZF-R1: that is to say, these two new models are no-compromise, highly-focused machines that offer riders a new level of engine and handling performance.
Using advanced race-bred engine and chassis technology developed from our class-leading YZ250F motocross machine and WR250F enduro bike, Yamaha’s designers set out to create two new lightweight 4-strokes which will bring competition bike performance to the street, and are set to excel in their respective roles.
WR250R development goals
- Outstanding acceleration and instantaneous throttle response
- Lightweight handling characteristics on and off road
- Competition bike performance with everyday convenience
- Environmentally responsible low-emission engine
- Lightweight and stylish image
New liquid-cooled 4-stroke DOHC 4-valve engine
The WR250R is equipped with a newly-designed engine that has been built to deliver outstanding acceleration and instant response that exceeds anything ever offered in the 250cc single-cylinder street-legal category. In fact, those street riders who have never experienced the awesome performance of Yamaha’s 250cc YZ and WR 4-stroke race bikes are sure to be amazed at the extreme levels of acceleration and instantaneous response delivered by the all-new Yamaha WR250R.
The newly-designed engine has been specially developed to exceed the expectations of today’s thrill-seeking performance-hungry riders, and features a compact liquid-cooled 4-stroke DOHC layout running with the same big 77.0 mm bore and short 53.6mm stroke as Yamaha’s Grand Prix winning YZ250F motocrosser and WR250F enduro bikes.
High compression pent-roof 4-valve cylinder head
The all-new short-stroke engine features a specially designed 4-valve cylinder head with a compact pent-roof combustion chamber which helps the WR250R deliver instant throttle response and remarkably strong performance right through the rev range to its maximum power output at 10,000 rpm. The 4-valve layout permits the use of a centrally-located spark plug for quicker ignition flame spread – and by offering a reduced surface area, the pent-roof combustion chamber allows more complete combustion of the fuel/air mix.
In order to achieve class-leading power output and outstanding response, the new cylinder head features a high 11.8:1 compression ratio, and utilises extra-large titanium intake valves which are of a relatively greater diameter than the exhaust valves compared to a traditional 4-valve design. In addition, the high-lift camshafts have been specially treated by our WPC (Wonder Process Craft) technique which involves spraying fine powder at a high speed to increase surface hardness and reduce frictional losses.
By optimising the complex relationship that exists between the size and number of valves, the valve skirt diameter, the valve seat angle and the camshaft profile, Yamaha’s engineers have succeeded in creating a new-generation lightweight 4-stroke single that is set to put the 250cc category back on the map.
Fuel injection with downdraft-type straight intake
In order to achieve class-leading throttle response together with fuel economy and environmental responsibility, the new WR250R is equipped with a fuel injection system – the first time this has been used on a Yamaha 250cc on-off road machine. The compact ECU unit receives data from a crank sensor, intake air pressure sensor and throttle position sensor, allowing it to calculate the engine’s optimum fuel volume, intake air volume and injection timing.
The fuel/air mix is fed to the 4-valve pent-roof combustion chamber via a long nozzle 12-hole two-directional injector with a wide timing range, and the highly detailed mapping of the fuel injection system ensures strong power delivery and instant throttle response right through the machine’s wide operating range.
Overall intake efficiency is greatly enhanced by the use of a new downdraft-type straight intake system. The use of this performance-boosting straight intake has been made possible by the adoption of a newly-designed rear suspension linkage which frees up space behind the engine. The intake is equipped with an air control valve, which, together with the EXUP system fitted to the exhaust, allows the ECU to accurately control the WR250R engine’s airflow from the intake right through to the exhaust.
Forged piston and plated cylinder
Highly efficient heat dissipation is one of the key factors which enables the new WR250R to deliver consistently strong performance at high rpm. A lightweight forged piston runs in the plated cylinder, and this combination of a heat-resistant piston together with the high heat transmission rate of the plated aluminium cylinder ensure that the engine is able to deliver a consistently strong supply of power.
In addition, the single radiator is equipped with a high-efficiency blower which maintains the system’s cooling function at lower speeds, and in doing so helps to achieve optimum power and reduced oil consumption.
Compact 3-axis layout
Using experience gained in the design of our World Championship-winning motocross and enduro engines, Yamaha’s engineers have created an extremely compact 3-axis layout for the new WR250R powerplant. By rearranging the relative positions of the crank shaft, main shaft and drive shaft and reducing the space between them – partly due to the elimination of the kick starter – we have been able to minimise the engine’s physical dimensions and achieve a greater concentration of mass, resulting in highly responsive handling qualities.
Wet-sump lubrication system
The new WR250R benefits from a wet-sump lubrication system which offers a number of advantages. Because this system contains all the lubricating oil in an oil pan beneath the engine, there is no need for an external oil tank or reservoir, and therefore no external oil pipes are required. The wet-sump design also requires fewer parts and is lighter, and the absence of external oil pipes also enhances the overall aesthetics of the engine.
Although the wet-sump design tends to be taller than its dry-sump counterpart because of the integral oil pan, the efficient design of the WR250R’s chassis has allowed the wet-sump to be accommodated between the tubes of the double cradle frame, thereby keeping engine height to a minimum, which allows for a generous 300mm of ground clearance.
Direct ignition coils
Direct ignition coils are featured on the WR250R – the first time this advanced system has ever appeared on a Yamaha on-off road machine. This compact system incorporates a booster in the spark plug cap, and eliminates the need for a frame-mounted ignition coil – as well as helping to reduce weight and free-up space above the engine.
Rare earth AC magneto
Yamaha’s engineers have pursued virtually every possible solution in order to reduce the overall dimensions of this advanced 250cc 4-stroke engine, and the use of a YZF-R series type rare-earth type AC magneto is another example of space-saving technology.
The use of fuel injection places greater demands on a machine’s electrical supply system, and this would typically require the fitment of heavier components to generate the greater capacity. However, by using elements such as neodymium (Nd) in place of the traditional ferrite materials, it is possible to create a particularly small and powerful AC magneto which offers increased electrical power with reduced size and weight.
Yamaha’s engineers have spent a great deal of time in creating a highly efficient smooth-action clutch which allows the rider to utilise the new engine’s performance to its full potential. Featuring an optimised stroke length, and equipped with thirteen compact plates (seven friction plates and six clutch plates), the WR250R’s clutch requires only a light lever load in order to slip the clutch when pulling away or exiting corners. The combination of the smooth-action clutch and high-performance short-stroke engine makes for a lively and exhilarating ride.
To help minimise overall weight, the new WR250R is equipped with a compact and efficient electric starter, while the kick starter has been eliminated. An auto-decompression function makes for easy starting with the push of a button, and for additional reliability the starter link features a torque limiter.
The WR250R’s 6-speed transmission has been specially developed to optimise the power characteristics of the new high-compression short-stroke engine. The ratios have been carefully selected to deliver impressive performance and strong driveability in a wide variety of situations, from city streets through to twisty trails and fast dirt tracks. And for increased durability the new transmission benefits from a shower-type lubrication system which ensures good gear lubrication and smoother shifting.
Overall exhaust efficiency is enhanced by the use of a new 3-stage expansion-type muffler which is located close to the machine’s centre of gravity in order to ensure lighter handling performance.
Environmentally responsible AIS, oxygen sensor and honeycomb catalyser
For even lower emissions the new WR250R is equipped with an oxygen sensor in the exhaust which feeds data to the ECU and adjusts fuel/air mix accordingly to ensure more complete combustion. In addition, an air induction system introduces air into the exhaust to re-burn any uncombusted fuel that is detected, and finally, the exhaust gases are cleaned by a honeycomb-type catalyser to reduce emissions even further.
New 3-section semi-double cradle frame
The WR250R features the first 3-section semi-double cradle frame ever used on a Yamaha on-off road model. This advanced new semi-double cradle frame has been developed using a great deal of the technology featured on our race-winning YZ250F motocross bike and the WR250F enduro machine, and consists of a cast aluminium/forged aluminium main frame, steel down tube and steel subframe.
The main frame features cast aluminium components for the front and rear sections, with forged aluminium parts for the other areas, and these are welded together to create an extremely light and enormously strong unit. Manufactured from thin-walled 25.4mm diameter steel pipe, the high-tensile single downtube offers a number of advantages over a conventional design. Firstly, by being a separate component it facilitates engine mounting during manufacture, and secondly, this design helps to achieve the desired ground clearance with the new wet-sump engine.
By using a combination of cast and forged aluminium for the main frame as well as a high-tensile thin-walled steel downtube and a steel subframe, the WR250R’s new 3-section semi-double cradle frame delivers an idealised balance of strength and rigidity for lightweight manoeuvrability, quick turning and agile handling.
Asymmetrical aluminium swinging arm
Virtually every aspect of the WR250R has been designed and manufactured to an advanced competition-type specification, and this commitment to high quality components can also be seen in the new aluminium swinging arm. Like the main frame, the innovative new swinging arm utilises a special combination of aluminium components in order to achieve the desired balance of strength and rigidity, and its low unsprung weight also ensures improved rear suspension performance.
The cross member is manufactured from cast aluminium, while the left and right arm sections are extruded aluminium, and the end pieces are forged aluminium. To achieve the optimum weight/rigidity balance and also enhance the bike’s aggressive cutting-edge styling, the new lightweight swinging arm features an asymmetrical cross section.
Fully-adjustable 46mm front forks
To complement the advanced new 3-section frame, the WR250R is equipped with a high-specification suspension package which has been designed to be able to handle a diverse range of on and off road riding conditions.
At the front end the WR250R is fitted with race-quality upside-down front forks offering a generous 270mm of travel, and equipped with flex-resistant 46mm tubes which deliver a good balance of rigidity. Like our motocross and enduro bikes, the WR250R’s forks feature lightweight aluminium triple clamps – cast aluminium for the handlebar crown and forged aluminium for the under bracket – and aluminium is also used for the steering shaft in order to minimise weight for responsive steering.
These 46mm diameter forks offer a full range of adjustability for preload and rebound/compression damping, and with a fork offset of 25mm and axle offset of 28mm, this high quality front end delivers neutral steering, excellent shock absorbing performance, and outstanding running stability on the road and in the dirt.
Fully-adjustable link-type rear suspension
The race-bred link-type rear suspension system has been developed using the knowledge gained from our World Championship motocross and enduro teams, and is one of the most advanced in the class.
The lightweight aluminium swinging arm operates a new shock featuring a 14mm diameter rod and large-capacity 46mm diameter cylinder which has been designed to handle everything from cobbled city streets through to extreme off road conditions. Like the front forks, the rear shock is fully adjustable for preload and rebound/compression damping, and offers 270mm of wheel travel, giving high levels of rider comfort in a wide variety of conditions both on and off the road.
Wave-type front and rear discs
Race-developed technology is evident wherever you look on the new WR250R, and another example of the close relationship between this new 250 and our race bikes can be seen in the wave-type 250mm front and 230mm rear discs. This design is used on our factory race bikes and also on our production YZ and WR models, and helps to reduce unsprung weight, as well as assisting in clearing any debris from the brake pads.
Digital LCD speedometer
The WR250R’s instrumentation has been designed to offer good levels of visibility and operability, while also being light and compact. The basic mode display includes a speedometer, clock and tripmeter, while the measurement mode includes a stopwatch and distance-compensation tripmeter.
Lightweight and compact new bodywork
Yamaha’s designers have concentrated their efforts on ensuring that weight is kept as low as possible, and that there is also a good concentration of mass. This has been achieved by using lightweight and compact components wherever possible - such as the rare-earth AC magneto and direct ignition coil. In addition, the new muffler has been positioned close to the machine’s centre of gravity, and the size and weight of the front and rear fenders and sidecovers has been minimised to help concentrate the machine’s mass.
Competition-type upright riding position
The handlebar/seat/footrest relationship has been carefully chosen in order to create a comfortable yet effective, upright riding position which makes the rider feel at one with the machine. The slim steel fuel tank offers excellent knee grip, and the frosted-finish competition-style seat allows easy weight shifting when riding off road. And with its 930mm seat height and 300mm ground clearance, the exciting new WR250R is ideally suited to challenging off road conditions.
WR250R Technical Highlights
- Newly designed 250cc liquid-cooled 4-stroke DOHC 4-valve
- Large lightweight titanium intake valves
- High-lift cams with extra-hard WPC* surface finish (*Wonder Process Craft)
- Bore x stroke 77.0mm x 53.6mm (Same as YZ/WR250F)
- High compression ratio of 11.8:1
- Pent-roof combustion chamber
- Maximum power developed @ 10,000rpm
- Electric start (no kick start)
- Fuel injection with long nozzle 12-hole injector
- Downdraft-type straight intake with air control valve
- Lightweight forged piston
- Ceramic composite plated cylinder
- Compact 3-axis layout
- Weight-saving wet-sump lubrication system
- Direct ignition coil
- Compact and lightweight rare earth AC magneto
- Smooth-action 13 plate clutch
- 6-speed transmission with shower-type lubrication
- EXUP exhaust and compact 3-stage muffler
- Air induction system and honeycomb catalyser
- 3-section semi-double cradle frame
- Frame uses cast aluminium, forged aluminium and steel pipe
- Lightweight aluminium swinging arm with asymmetrical cross section
- 46mm upside down forks with 270mm travel
- Link-type rear suspension with 270mm travel
- 300mm ground clearance
- Upright seating position offering optimum rider manoeuvrability
- Tall 930mm seat height for effective off road performance
- Multi-function digital instrumentation
- Lightweight bodywork with excellent mass concentration
- Wave type 250mm front disc and 230mm rear disc
- LED tail light
||Liquid cooled, 4-stroke, DOHC, 4-valve, forward inclined
||inclined single cylinder
|Bore & stroke
||77.0 X 53.6 mm
||11.8 : 1
||22.6 kW (30.7 PS) @ 10,000 rpm
||23.7 Nm (2.42 kg-m) @ 8,000 rpm
|Carburettor / Fuel supply
||Electronic fuel injection
||Wet, multiple-disc coil spring
||Constant mesh, 6-speed
|Primary reduction ratio
|Secondary reduction ratio
|Gear ratio-1st gear
|Gear ratio-2nd gear
|Gear ratio-3rd gear
|Gear ratio-4th gear
|Gear ratio-5th gear
|Gear ratio-6th gear
||Semi double cradle
|Front wheel travel
||Swingarm (link suspension)
|Rear wheel travel
||Single disc, Ø 250 mm
||Single disc, Ø 230 mm
|Min. ground clearance
|Fuel tank capacity
|Specification are subject to change without notice, in accordance with national regulation and legislations