Yamaha launched the first production four-stroke motocross bike with the YZ400F back in 1998, one year after the Yamaha OWH2 four-stroke prototype's victory at the 1997 Las Vegas Supercross. However, despite their storied history with the bike, Yamaha hasn't won a Supercross championship since James Stewart won in 2009, or a Motocross championship since Grant Langston won in 2007.
Yamaha aims to change all of that this year with their all new 2018 Yamaha YZ450F. It has a new motor, new chassis, new body, and new electronics that will go a long way to putting it back on top of the podium while also making it even better for the dirt enthusiasts.
Yamaha has revised the cylinder head and camshafts by giving the intake port a straighter shape, increasing the valve openings and valve timing overlap, and modifying the intake and exhaust camshaft angles. They've also given the exhaust a longer pipe head, though it is now narrower at the junction, decreasing from 41mm to 38mm. Yamaha also swapped the old Keihin throttle bodies for new Mikuni ones, though they remain 44mm and with 12-hole injectors. This adds a new push-type knob cold start system and more compact throttle position sensor. The result is more controllability at low to mid-range rpm.
Yamaha also revised the piston and piston pin, swapped for a spark plug with a longer electrode, changed the shape of the ignition coil, and revised the ECU settings, all of which they claim makes for stronger and longer power at the top of the rev range.
The clutch has also been reworked to offer smooth clutch engagement. To achieve this, the pressure plate thickness was changed and given a ribbed shape, with the rigidity of the center decreased while the rigidity of the outer surface increased. Surface grinding that was previously only applied to one side of the clutch plates has now been applied to both, while the clutch springs have improved squareness tolerance which means they align straighter when compressed.
The 2018 YZ450F has an all new bilateral beam aluminum frame, with a straight tank rail replacing the previous S-shaped one, a new tension pipe, and new motor mounts which attach in more of a rectangular shape. The layout of the frame has been revised to create a larger triangulated absorption zone, which adds 25% vertical rigidity, 15% torsional rigidity, and 9% horizontal rigidity. These changes add to the bike's stability while also making it feel more nimble.
The steering pipe, triple clamps, and handlebar mounts have also been revised, moving the steering pipe forward 6mm, increasing the offset of the triple clamps from 22mm to 25 mm (which increases trail by 3mm from 118mm to 121mm), and raising the handlebar mounting position by 5mm.
To help reduce unsprung weight, Yamaha reworked their rims by altering their shape and density. Overall, they save 40 grams on the front and 70 from the rear. They've also reduced the thickness of the handlebar by using a higher strength material, saving another 111.5 grams.
The suspension has also been reworked, with Yamaha opting for a KYB fork with new internals with a 1mm larger cylinder and piston (25mm), a mid speed valve that now uses a leaf-spring type rather than coil spring type, and a new pressure piston. The shock has a new 30cc larger reservoir and a new, thinner and lighter spring that has a stiffer spring rate (56 to 58N/mm).
While it may look similar, the bodywork of the new YZ450F is also all-new, based now on some key changes that will improve rider feeling and ease of use and maintenance.
There's a new airbox and air filter, which is easily accessible on top of the tank and requires no tools to swap out. The air cleaner joint volume has been increased, and the air ducts are now integrated into the front shroud.
The fuel tank has been reduced from 1.9 gallons to 1.6 gallons, with Yamaha using this change to decrease the width and save weight (they say it's still plenty for a 45-minute moto). This also allowed for an 18mm narrower seat.
The radiator has also been moved to allow the side panels to be 16mm narrower at your knees, though it actually has a 4.5% bigger surface area than that of the 2017.
The 2018 Yamaha YZ450F comes with an onboard computer and a smartphone app that lets you tune fueling and ignition, keep track of your settings at different tracks, provide trip and usage data, and share data like throttle position and engine rpm in real time.
The whole system comes standard with the bike and seems fairly intuitive from the presentation we saw (although I wouldn't go diving into the fuel mapping and ignition timing without knowing what I was doing or getting settings from the forums).
The 2018 Yamaha YZ450F comes in the standard blue and white as well as a white/cyan and has an MSRP of $9,199