Yamaha’s 2007 WR250F
Yamaha’s 2007 WR250F
Yamaha’s record in enduro competition is truly outstanding, with their WR250F dominating four World Championships in succession between 2001 and 2004.
This class-leading performance is based on a platform of performance and reliablitity which has led to to the WRF range regularly featuring as Australia’s top selling motorcycles.
Yamaha was the first manufacturer to develop the new wave of lightweight, free-revving 4-stroke enduro models, and for 2007 they are raising enduro machine design to another level with the next generation WR250F.
Featuring the most advanced cutting-edge engine and chassis technology ever seen on a Yamaha enduro machine, the all-new 2007 WR250F offers today’s enduro rider a very real advantage at every level.
A new lightweight aluminium semi-double cradle frame carries a new high performance engine that delivers increased levels of useable power – high-tech packages that are completed by totally new ergonomic bodywork.
The WR250F engine has been completely reworked in order to ensure class-leading engine performance in the extremely wide range of operating conditions associated with enduro competition. Revised camshaft profiles enhance the bike’s low to mid range performance, the very place where enduro riders need to have the edge.
In addition, we’ve also revised the intake and exhaust cam timing for increased low to mid range flexibility, with revised carburettor settings and a new CDI with modified ignition mapping. To match these changes we have equipped the new 2007 WR250F with a closer ratio transmission. The step between third, fourth and fifth gear ratios is reduced to minimise the rpm reduction when shifting up, allowing the rider to stay within the optimum rpm range.
These significant changes deliver increased punch right where it matters most, giving the WR250F rider a distinct advantage. The engine is equipped with a new dry sump lubrication system featuring a compact 720cc oil tank located in front of the engine. This design helps to centralise mass for lighter handling performance compared to the 2006 model.
In addition to these external changes the new engine incorporates a reshaped strainer compartment in the crankcase, giving a better oil circulation route, and the new strainer design increases crankcase volume, thereby reducing oil agitation resistance to give enhanced performance. To handle the increased engine performance and ensure stable running over longer periods, the 2007 WR250F runs with larger radiators offering a greater frontal surface area.
These highly efficient radiators are also fitted with lightweight reinforcement brackets that increase the system’s rigidity for improved durability in the event of a fall. To accommodate the new aluminium frame design and also match the revised camshafts and timing, the exhaust system features a longer, smaller diameter pipe and a shorter silencer mounted further forwards.
2007 WR250F Engine Technical Highlights
· 250cc 4-stroke liquid-cooled
· DOHC 5-valve
· Bore x stroke 77mm x 53.6mm
· Electric start
· Based on YZ250F design
· Special WR cam profile and timing for stronger low to mid range performance
· Revised carburettor and CDI settings
· New design exhaust system
· Revised 5-speed transmission with closer 3rd, 4th and 5th gears
· New dry sump lubrication with front mounted external oil tank for optimised mass concentration
· Large capacity reinforced radiators
· Revised intake layout
The 2007 WR250F’s new lightweight aluminium semi-double cradle frame is based on the YZ250F design, and is one of the most advanced in the off road world. Unlike some other aluminium frames, the WR250F’s semi-double cradle frame offers a lower centre of gravity than the beam-type off-road frame design, and can also be constructed using fewer components.
The Yamaha semi double cradle frame has been manufactured using three types of aluminium cast, forged, and extruded that has enabled our designers to build in an optimum balance of rigidity. Forged aluminium is used for the upper portion of the main tube as well as the dividing point of the cradle, and around the swingarm pivot.
Cast aluminium is used at the head tube and parts of the main frame. Aluminium pipe is used for the under loop and extruded aluminium is used at the swingarm pivot. This sophisticated frame consists of just nine components welded together using Yamaha-exclusive technology to create a single unit offering the right amount of “forgiveness”, and a low centre of gravity. Unlike weight or horsepower, forgiveness is difficult to quantify, and yet it is a crucial quality that has a major influence on the handling characteristics of every dirt bike.
The actual level of the balanced rigidity that is engineered in to the WR frame has been arrived at after many thousands of hours of real world testing by our development riders. Yamaha’s previous steel framed WR’s were rightly praised for their superb handling characteristics thanks to their idealised rigidity balance, and the new generation aluminium frame fitted to the WR250F is once again ready to set new standards.
In the same way that the character of a machine’s power is just as important as its maximum power output, so too is a machine’s weight distribution just as significant as its overall weight. Whereas an off road beam frame tends to concentrate much of its mass high up on the machine, the Yamaha semi-double cradle design has much of its mass low down. This feature, combined with the new low centre of gravity dry sump engine, ensures that the new WR250F delivers lighter handling performance. The new frame’s balanced rigidity or controlled flex combined with the inherently low centre of gravity of a semi-double cradle layout makes for a class leading ride quality that translates into winning handling performance for the enduro racer, and class leading comfort for the recreational dirt rider.
For optimum rider control in various situations the WR250F features a number of enduro-specific dimensions compared to the YZ250F, including a lower seat height, and lower footrests position. The stainless steel footrest design is new for 2007, and features a 11.2mm wider front-to-rear dimension for reduced pressure on the rider’s soles a detail that can make the difference when you’re in the saddle all day. Combined with the low centre of gravity and balanced rigidity chassis, these detail changes make for lighter handling qualities, notably in tight, woody terrain where lock-to-lock slow speed turns are often experienced.
In keeping with its all-new engine and chassis, the 2007 WR250F features completely new bodywork which includes an 8-litre fuel tank with YZ-style shrouds, a compact new 35/36.5W headlight, new side covers and rear fender, and a lightweight LED rear light assembly. Although the seat is mounted lower than on the YZ, the WR250F seat is actually thicker and is manufactured using more comfortable foam for improved comfort. We have also paid particular attention to the area where the front of the seat meets the 8-litre fuel tank in order to enable easy weight shifting when approaching corners.
A new one piece plastic wrap-around resin engine guard is 80g lighter than the previous three part aluminium design, and is easily removed by undoing just three bolts. The ultra-light design offers greater protection to the underneath and sides of the crankcases, and also helps to prevents mud buildup under the new engine. The new air cleaner box can be opened with the release of a single fastener, and this feature, together with a quick-release air filter mechanism, makes for easy filter changes whether you’re in the workshop or the parc ferme.
New Pro Taper aluminium handlebars help to keep weight to a minimum and underline the attention to detail on this high quality enduro bike. Offering a better riding position, these Pro Taper bars are just one example of the wide range of high quality components that mark the 2007 WR250F out as one very special dirt bike that is ready for anything, straight out of the crate.
For the first time on a WR model, the new WR250F comes equipped with lightweight wave type front and rear disc brakes which reduce unsprung weight by 80g and offer improved braking and pad cleaning performance. More weight is saved by the use of forged upper and lower triple clamps which grip the 48mm front forks. Also new are forged handlebar clamps, and this significant reduction of weight which is situated high up on the steering assembly helps to accentuate the light steering feel of the new WR.
A new rear shock is equipped with a larger sub tank, and overall length is increased to give stable performance over longer periods, while the 48mm front forks run with revised enduro-specific settings to match the new aluminium chassis. In common with the 2007 YZ, the new WR250F is equipped with a range of ultra light components, including a new rear axle, chainguard, chain slipper and a variety of lightweight nuts and bolts. Other important features include the forged aluminium sidestand, 18-inch rear wheel, enduro silencer, O ring chain and a new more compact 536cc catch tank. The 2007 model also features a compact new digital rally computer and speedometer.
RRP (inc GST) for the newly released model is just $11,699.
2007 WR250F Chassis Technical Highlights
· New lightweight aluminium semi-double cradle frame
· Special WR dimensions and new footrests
· New generation YZ-style bodywork
· Special WR seat
· Wrap around plastic resin engine guard
Pro Taper handlebars
· Wave type discs
· Lightweight forged triple clamps
· Uprated rear suspension
· Lightweight components
· 18 inch rear wheel
· Forged aluminium sidestand
· 536cc catch tank
· Enduro silencer
· O ring chain
· Compact digital speedometer
· New graphics
The record shows that the WR250F is the most successful 250cc 4-stroke enduro machine ever built, with four consecutive world titles. Its performance at world, national and local level underlines not only how good this bike is, but also how it can be a winner whether ridden by a factory pilot or club rider. This is the reason that so many riders of all abilities have chosen the WR250F time after time and why so many riders have come back to it after trying something else.
Yamaha’s 2007 WR450 Release is HERE