In 2014, Yamaha introduced an all-new YZ250F took the class by storm. It was consistently finishing with high marks in industry testing, and it eventually rewarded Yamaha with the AMA 250cc National Motocross Championship, a first since the class shifted to only four-stroke-powered bikes in 2009.

So now you’re wondering how this relates to the company’s new YZ450F, and here’s how: the bigger YZ brother in Yamaha’s lineup has essentially featured many of the same upgrades found on the 2015 YZ250F since 2010, specifically its rearward-slanted-cylinder and reversed cylinder head engine that is found on the YZ250F. Unfortunately for Yamaha, the YZ450F has not had the same level of success in dominating the competition as the 250 did this year during the motocross season.

The hardest thing for Yamaha to do was convince consumers that the 450F’s radical new design was in fact superior to the previous version, which had just come off winning the Monster Energy AMA Supercross Championship and was clearly a winner. While we believe that to be true, we also think that this new motor created challenges in chassis tuning for Yamaha. There was little question that the YZ450F was fast, but it took a few seasons for Yamaha engineers to really fine-tine the chassis and suspension to be able to truly harness and the added power of the new 450F motor.

Entering the 2015 model years, that could all change, as Yamaha believe its 2015 YZ450F best reverse-motor model it has produced to date. Yamaha invited us to Cahuilla Creek Motocross Park near San Diego to test the bike, and we came away feeling that Yamaha may finally have made the right changes to put the YZ450F over the top. Yamaha didn’t actually need to make massive improvements upon the YZ450F in our opinion, as it underwent a complete overhaul in 2014. During our test of the 2014 YZ450F, we noted the 450’s redesigned, liquid-cooled, fuel-injected, 449.7cc, DOHC single was strong from bottom to top, but we felt the low-end throttle response was lacking until we tweaked its ECU to richen the fuel curve. We also noted a tendency for the chassis to be nervous at high speeds because the fork tended to dive over small and large impacts. Yamaha has addressed these issues, and more, with the 2015 model. At $8590, the YZ450F only costs $100 more than last year, but it feels like a completely new bike.

The 2015 YZ450F engine featuress the same 97.0 x 60.8mm bore and stroke as last year’s model, and it retains all of the changes made to improve its power delivery over the 2013 model. They include a larger airbox volume, 1mm larger (37mm) titanium intake valves and .5mm larger (30.5mm) exhaust valves, along with reshaped intake and exhaust ports and a slightly increased combustion chamber volume. However, Yamaha engineers have incorporated new ECU and ignition settings to improve the 450’s throttle response as well as give it more low-end torque and better top-end overrev than the 2014.

Chassis and suspension changes are also minor for 2015. Yamaha changed the thickness, shape and material of the lower motor mounts to retune the flex characteristics of the 450’s Bilateral Beam aluminum chassis. The new mounts are made out of steel rather than aluminum, but they are also 2mm thinner and feature a U-shape rather than a triangulated shape. Corresponding changes were made to improve the 450’s 12.2-inch travel, 48mm KYB Speed Sensitive System (SSS) front fork. Its outer fork tubes are less rigid than before, and the fork spring stiffness has been increased to 5.0 kg, up from 4.9 kg. Out back, the 450F’s fully adjustable KYB monoshock also received minor setting changes to keep its 12.4 inches of rear wheel travel working in harmony with the fork.

Cahuilla Creek was a good location to test the new YZ450F, because it has a fast layout, with sandy terrain that features deep berms and big jumps. Joining us for the test would be racer Ryan Abbatoye, the same man who delivered our impressions of the 2014 model, so we knew that he would be able to discern whether or not Yamaha’s changes were actual improvements. It was clear to Abbatoye immediately that the changes to the fuel and ignition curves yielded a much cleaner power output. 

The YZ450F’s trademark torque is still as sweet as ever. Right from the hit of the throttle, it generates tremendous lunge with a broad torque curve that allows the rider to keep the YZF in the same gear a lot longer than other bikes in its class. The power builds smoothly and with tremendous authority all the way to the rev limiter, and now it does so without any hesitation in throttle response through its Keihin 44mm throttle body.

We put our test bike on the dyno to see what kind of power it was making, and we came away impressed. The YZ450F topped 52 rear-wheel horsepower, settling in at 52.32 hp at 9000 rpm, with 31.74 lb.-ft. of peak torque at 8250 rpm. Even more impressive is that the 450 motor maintains 30 lb.-ft. of torque from 6250 rpm all the way past 9250 rpm before it begins to tail off, and the engine maintains 50 hp from 8500 rpm all the way to its 11,000 rpm rev limit. That’s big power!

Abbatoye clearly had a lot of fun blowing up Cahuilla Creek’s sandy berms and rocketing over its big jumps on the YZ450F.

“This bike is definitely a lot snappier than before, and it makes so much power that it is easy to ride in a higher gear now,” Abbatoye said. “Remember that last year I said I felt like I wanted to be in-between gears in the transmission a lot. Not this year. I really like it. It makes pro-level power, but the average rider can just ride it a gear high, and it still makes plenty of torque to launch off the corners and over jumps.”

Part of the motor’s superb feel is due to the fact that Yamaha also dropped the rear sprocket one tooth, going from 49 teeth back to 48 teeth, same as was used on the 2013 model. The YZ450F’s motor is so brawny that it easily takes up the slack of the slightly taller gearing, and the new final gearing matches the ratios in its five-speed transmission to the power output better. If you do need to bang a shift, the 2015 will feel smoother than last year’s because Yamaha changed the bearing on the gear stop lever from a ball bearing-style to a positive roller bearing. If you want to ride in a taller gear, there’s no need to worry about brutalizing the YZ450F’s clutch because it can take the abuse. Yamaha improved it in 2014 by adding 10% stiffer clutch springs and new clutch plate friction material. So, hammer away.

Speaking of hammering, Abbatoye also noticed a big difference in the way the 2015 YZ450F tracks through corners and handles bumps at high speed. Its basic chassis numbers are the same as 2014, with a 58.3-inch wheelbase, 27-degree rake and 112mm trail, and Yamaha claims a wet weight of 245 lbs. for the YZ450F. Ours tipped the scales at 248.5 lbs., placing 119.4 lbs. on the front wheel and 129.1 lbs. on the rear wheel. Its numbers may be unchanged, but the tweaks made to its chassis and suspension have definitely yielded much better feedback than last year’s bike. Whereas the 2014 model exhibited slightly heavy steering and high-speed jitters even after we made changes to dial-in its suspension, the 2015 turns easier and responds much better to clicker adjustments.

“Once we set the sag, it felt pretty balanced, maybe just a little stiff overall for someone my weight (170 lbs. in full riding gear),” Abbatoye said. “We softened up the compression in the front and went out a little bit on the high-speed (compression adjuster) the rear, and that worked pretty well over any of the bumps I hit at Cahuilla. It turns really well, but coming out of a corner you have to be careful with how you feed it throttle because it wants to wheelie, so you want to make sure that you don’t get lazy. You need to stay over the front and control the bike.”

Bringing the bike down from speed are the same 250mm front and 245mm rear rotors as the 2014 model. Yamaha has yet to step up the diameter size on its front rotor, but the Nissin twin-piston front brake and single-piston rear brake do a fine job. They’re linear and strong without being snatchy. For 2015, Yamaha has fitted the YZ250F’s new, black-anodized Excel rims with Dunlop’s excellent new-gen MX52 tires. The MX52s are designed to excel in medium to hard terrain, yet they worked well in the Cahuilla sand, delivering excellent traction and very good feel. Call us spoiled, but we just happen to know that the MX32s work even better.

Yamaha has worked overtime to centralize the YZ450F’s mass, and its efforts have yielded an extremely slim and compact cockpit as well. Hiding the fuel filler neck for the mid-mounted 2.0-gallon fuel tank allow the rider to climb farther forward on the slim, narrow seat allows the rider to get farther forward on the Yamaha on than on other brands, making the bike easier to crank into turns.

Of course, the YZ450F’s styling is worth noting as well. Its slim bodywork is adorned with “bold new” graphics, but what is cool about the Yamaha is that the graphics are actually embedded in the radiator shrouds, which makes them much harder to peel, and thus more durable. Other detail changes include new Dzus-fasteners with pull tabs that allow the air box lid (or the top of the faux fuel tank) to be removed without requiring a tool. Once again, the YZ450F is available in two color schemes: Team Yamaha Blue/White or the White/Red that recalls Yamaha’s old international racing colors. Both machines also get a snazzy new D.I.D. chain with gold-anodized plates and a new corrosion-resistant coating.

When you boil it down, the 2015 Yamaha YZ450F isn’t all that different than the 2014, and yet the changes that Yamaha made really help the 450 live up to its true potential. It is worlds better than the 2014. All that remains to be seen is whether or not it can become the class champion. 

2015 Yamaha YZ450F Specifications
MSRP: $8590
Engine Type: 449.7cc liquid-cooled DOHC 4-stroke; 4 titanium valves
Bore x Stroke: 97.0 x 60.8mm
Compression Ratio: 12.5:1
Fuel Delivery: Yamaha Fuel Injection (YFI), Keihin 44mm throttle body
Ignition: TCI: Transistor Controlled Ignition
Measured Horsepower: 52.32 rwhp @ 9000 rpm
Measure Torque: 31.74 lb.-ft. @ 8250 rpm
Transmission: Constant-mesh 5-speed; multiplate wet clutch
Final Drive: Chain
Suspension
Front: KYB Speed-Sensitive System, inverted fork; fully adjustable, 12.2-in. travel
Rear: Monoshock, adjustable preload and rebound damping, 12.4-in. travel
Brakes
Front: 250mm rotor disc brake w/two-piston caliper
Rear: 245mm rotor disc brake w/single-piston caliper
Tires
Front: 80/100-21 Dunlop MX52-FA
Rear: 120/80-19 Dunlop MX52
Seat Height: 38.4 in.
Wheelbase: 58.3 in.
Rake: 27 degrees
Trail: 120mm
Ground Clearance: 13.2 in.
Fuel Capacity: 2.0 gal.
Claimed Wet Weight: 245 lbs.
Measured Wet Weight: 248.5 lbs. (48% front/52% rear bias)
Color: Team Yamaha Blue/White; White/Red