2018 Yamaha YZ450F Preview

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The 2018 Yamaha YZ450F promises to advance technology in the sport of motocross by becoming the world’s first Wi-Fi-equipped production dirtbike, capable of allowing the user to tune the engine’s ECU with the use of an Apple or Android smartphone. Yamaha’s all-new Yamaha Power Tuner iOS and Android app connects to a WI-Fi communication control unit on the 2018 Yamaha YZ450F to allow for instant fuel and ignition mapping changes trackside when the engine is not running.

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Even cooler than that, the app features a “log” function that allows the user to keep a record of such data as riding location, riding conditions, bike settings and more. It can also log other important data, such as engine rpm, throttle position, engine coolant temperature and more. There is also a maintenance function with customizable trip meters to monitor run times for maintenance scheduling. All of this data is shareable as well.

The 2018 Yamaha YZ450F is once again available in two color choices. The alternative white body color is accented by different shades of blue rather than Yamaha’s usual red and black accents.

The 2018 Yamaha YZ450F is once again available in two color choices. The alternative white body color is accented by different shades of blue rather than Yamaha’s usual red and black accents.

New Engine

The 2018 Yamaha YZ450F engine introduces a host of changes, and perhaps the biggest is its new electric start function. But, don’t be fooled into thinking that Yamaha simply adapted the current technology in the YZ450FX and WR450F just to make the 2018 YZ450F go electric. Instead, its fuel-injected, liquid-cooled, DOHC, single-cylinder engine is all-new from the cases up, and it places the electric starting mechanism behind – rather than in front of – the YZ’s rearward-slanted cylinder for better mass centralization than the WR/FX engine. Powered by a lightweight (1.5-lb.) Lithium-ion battery that boasts a class-leading 13.2 volts of juice, the centrally located starter drives to the clutch basket when starting the bike.

The YZ450F’s starter mechanism is located behind the cylinder to better centralize engine mass.

The YZ450F’s starter mechanism is located behind the cylinder to better centralize engine mass.

Never short on power since the introduction of its rearward slanted engine design, the YZ450F is claimed by Yamaha officials to be easier to ride than ever, and better power management was a key design goal. Starting from the top, the 2018 YZ450F features an all-new cylinder head with a lighter casting than the previous version. The new head features straighter intake ports, and Yamaha engineers also developed new camshaft profiles that offer 0.5mm more lift on the intake cam and 0.4mm more lift on the exhaust cam along with 8° more overlap to fill the new cylinder, which is actually positioned 2° more upright than on the previous engine to optimize weight distribution in the new chassis.

The YZ450F’s piston is all-new as well, with Yamaha electing to go with a bridged box design to increase strength and rigidity. The new piston also weighs about 6 grams less than the old one, thanks to a slight reduction in crown thickness. Compression ratio has been increased from 12.5:1 to 12.8:1, and a Diamond-line Carbon piston pin is used to reduce friction inside the engine. To accommodate the electric starting system, the YZ’s crankshaft is also new, with increased inertia and a balance ratio that has been changed from 50% to 60%. However, the rotor and stator now have less inertia because the rotor width has been reduced by 2.1mm and the diameter has been decreased by 4mm. Thus, says Yamaha, the overall inertia of the crank and rotor/stator assemblies is the same as the 2017 model.

The 2018 Yamaha YZ450F engine has received a complete redesign with the goal of attaining more controllable low- to mid-range power and a longer, stronger top-end pull.

The 2018 Yamaha YZ450F engine has received a complete redesign with the goal of attaining more controllable low- to mid-range power and a longer, stronger top-end pull.

Fuel injection on the 2018 Yamaha YZ450F is still handled via a 44mm throttle body and a 12-hole injector, but for 2018 Yamaha has spec’d a Mikuni throttle body rather than a Keihin; the Mikuni unit was favored for its smaller Throttle Position Sensor, but its cold-start function actually represents a neat tech update as well: The cold start button on the throttle body must be pulled manually before starting the bike, but once the engine is warm, deactivating the cold start is a simple matter of blipping the throttle or rotating it forward from its neutral position. Also, to optimize spark, a new spark plug with a longer electrode is used, and the plug wire connection is more secure via the addition of a cap holder. The ECU settings have also been revised to tailor the power character of the engine, and the 2018 retains the Launch Control System (LCS) to optimize engine output for quicker, more efficient launches off the starting gate.

The YZ’s five-speed transmission and clutch are updated to provide a better clutch feel and more durability. The pressure plate is more concave than the previous version, and its rib shape and plate thickness has been revised to provide less center rigidity, which is made up for by a slightly increased outer rigidity. New steel clutch plates that feature surface grinding on both sides of the plate are also used to help give the clutch a more direct feel at the lever. The clutch system still does not use a hydraulic actuator, but new clutch springs are claimed to improve clutch action by offering a straighter alignment when the clutch lever is pulled. The transmission gears have been beefed up via 1mm additional width in second, third and fourth gears.

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Other changes for 2018 include larger radiators that are angled more directly to the incoming air stream for better engine cooling and a new version of Yamaha’s wraparound exhaust pipe design. The radiators are mounted 6° more vertical and 6mm closer to the frame to help slim the ergonomics. The surface area of radiator core has been increased 4.5% by reducing the tank size by 10mm. The 2018 exhaust system uses a 12mm longer head pipe and a smaller 38mm junction, and the muffler is now rubber-mounted to be more resistant to vibration. Overall, Yamaha claims that the new exhaust offers more controllable low- to mid-range power while also centralizing mass more effectively by moving the rear end of the exhaust pipe farther forward to place the muffler closer to the center of the mass.

Slimmer Chassis

The 2018 Yamaha YZ450F’s bilateral beam aluminum chassis is all-new. The flatter, slimmer frame features more extruded sections and does away with the hydroformed main spars.

The 2018 Yamaha YZ450F’s bilateral beam aluminum chassis is all-new. The flatter, slimmer frame features more extruded sections and does away with the hydroformed main spars.

If you read DirtBikes.com’s 2017 450cc Motocross Shootout, then you know that the biggest gripe our testers voiced about the YZ450F had to do with its wide-feeling chassis. For 2018, Yamaha engineers went to work to give the mid-section of the YZ450F a much slimmer feel. To that end, an all-new bilateral beam frame with taller, flatter and 6mm thinner spars has been designed to replace the old chassis. The shape is also completely different, with straighter, extruded upper spars replacing the curvy, hydro-formed spars of the 2017 YZ450F. The tension pipes that connect the spars to the downtubes on the frame are also extruded rather than forged to provide the desired chassis rigidity. The shock mount casting is larger than the 2017. The rear frame spars have been redesigned, and the cradle pipes have also been changed to a rectangular shape. All-new aluminum engine mounts replace the steel units used on the 2017 YZ450F, and the cylinder head stay connection point has been moved from the front to the rear of the cylinder head.

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Yamaha claims that the new chassis is designed to deliver 15% greater rigidity on the lateral axis, 9% greater rigidity on the horizontal axis and 25% percent greater rigidity on the vertical axis for better cornering manners more consistent flex and better bump absorption while retaining the YZ’s renowned straight-line stability. The steering pipe that has been repositioned that is 6mm farther forward than the 2017, and the triple clamp offset that has been decreased from 25mm to 22mm. Trail is increased 3mm to 121mm (4.7 inches).

Next-Gen KYB Suspension

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The 2018 Yamaha YZ450F also receives upgraded suspension in the form of next-generation KYB components. Up front, the Speed Sensitive System (SSS) coil spring fork boasts new internals, including a cylinder and piston that has been increased from 24mm to 25mm. For easier tuning by suspension gurus, the fork now features a leaf-spring rather than a coil spring in the mid-speed valve. The pressure piston shape has also been changed and relief holes have been added for better bump sensitivity. Front suspension travel is 12.2 inches.

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Out back, a new, fully adjustable KYB shock features a 30cc larger oil reservoir and a new shock spring made of thinner material and with fewer windings, reducing the spring weight by 4.8%, to 210 grams. The shock valving has been revised to allow more oil flow for a more controlled damping feel. Yamaha continues to bounce back and forth with shock spring rates on the YZ450F to suit whatever chassis changes it has made from year to year. For 2018, the shock spring rate is back to 58N/mm (from 56 N/mm in 2017). Rear suspension travel is 12.5 inches.

Slimmer Ergonomics

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The 2018 Yamaha YZ450F is also claimed to offer a slimmer feel via the addition of new, lighter and more compact bodywork that is placed lower on the chassis. Also, the reduces the overall width of the seat/tank area by 18mm. Part of the decrease is due to a narrower seat that is also flatter from front to rear. The seat height has been reduced by 8mm at the front and almost 20mm at the back. Yamaha also slimmed up the fuel tank albeit at the expense of some fuel capacity. The new tank carries only 1.6 gallons of fuel, .3 of a gallon less than the 2017 tank, although Yamaha officials claim that there is still more than enough capacity to feed the 2018 YZ450F for a 40-minute moto. The radiator shrouds also incorporate a new air duct with a concave shape that is narrower at the knee contact points for less-restricted rider movement. Lastly, the 2018 YZ450F will once again be available in two colors: factory Yamaha blue or white.

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The 2018 Yamaha YZ450F is expected to arrive in dealerships in August. MSRP has been set at $9199. That’s a $500 jump in price from the $8699 of the 2017 model, but considering the complete redesign and the all-new Wi-Fi tuning technology that the 2018 model offers to boot, it may be money well spent.

For more information on the 2018 YZ450F and all Yamaha motocross models, visit YamahaMotorsports.com/motocross.

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(motorcycle.com, https://goo.gl/9Drlmk)

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