Few modern-day motorcycles have a history like the Yamaha YZ250F. Debuted in the early 2000s, it was the very first four-stroke motocross machine of its displacement and it immediately indicated that the two-stroke 125cc reign that we had come to know and love was near the end. Yamaha refined the machine through the early years with new frames and engine designs, but not at the pace other OEMs and by 2011, the outdated carbureted engine and aluminum frame were among the least liked in the division. That all changed in 2014 when Yamaha started with a clean slate and dropped a more powerful fuel-injected powerplant into a reconfigured chassis and again became a leader in the 250 class. Even with all of the accolades, including professional championships through the Star Racing team and praise by the media, Yamaha decided that the YZ250F would benefit from further improvement and for 2019, the bike features another all-new frame, engine package, and assorted components.
Yamaha aimed their efforts their efforts improving the mid to top power characteristics of the engine, making the chassis more nimble on the track, and the overall layout of the bike easier for the rider to maneuver around. To coax more performance out of the engine, Yamaha refined the cylinder head to make it more efficient through a new intake camshaft, straighter and smoother intake and exhaust ports which increased flow rate, a new crown shape piston with a higher compression ratio (from 13.5:1 to 13.8:1), a new valve train with larger lifter buckets and increased valve spring rates, dual electrode spark plug, a change to a 44mm Mikuni throttle body with 12 hole injector, and an updated exhaust head pipe design. In addition to these changes to the cylinder head, Yamaha dropped in a new clutch that has a higher heat capacity through larger and thicker plates and six clutch springs that are matched to a transmission that is made from high impact steel. The new ECU is connected to Yamaha's innovative smartphone-based Power Tuner app that allows riders to alter the fuel and ignition mapping for track conditions or riding styles, while a handlebar mounted system allows a rider to switch between two preloaded maps on the fly. All of this is brought to life with the electric starter that is connected to a 2.4Ah, lightweight lithium-ion battery. With the addition of the electric starter, Yamaha crafted new engine crankcases that feature a more upright cylinder incline and eliminated the housing and components for the traditional mechanical starter.
When compared side by side, it's easy to spot the changes to the chassis from 2018 to 2019. Like every other Japanese OEM, Yamaha remained with aluminum as their material of choice for the chassis, but the dimensions and construction of the bilateral beam frame have been greatly changed and the tank rails of the 2019 are extruded aluminum and have a much straighter profile. The tension pipe, steering pipe, swingarm bracket forging, engine mounts, shock mount, cradle pipe, and fork lugs have all changed from 2018 to 2019 through construction materials, dimensions, or placement and together this creates a large triangle of energy absorption. With this configuration, the vertical, horizontal, and torsional rigidity of the chassis have all been increased and the flex characteristics have been made smoother.
Another side-by-side comparison between 2018 and 2019 YZ250F motorcycles make the changes to appearance obvious. In an effort to slim the rider cockpit area considerably, Yamaha has mounted the new radiators more vertically and 6mm closer to the frame and then narrowed the fuel tank and seat width by 16mm and 18mm, respectively. It must be noted that the change to the fuel tank has dropped the overall capacity from 1.9 gallons to 1.6 gallons, but the total volume is said to still be more than enough to finish a full 30-minute moto at pro rider speeds. Yamaha has replaced the multi-piece radiator shroud and airbox cover setup with a new smaller and less complex design that has been shaped to be slimmer near the frame and gradually open out around the radiators for improved rider movement, and the seat is now flatter and lower than before. Every piece of plastic, from the front fender to the rear fender, has been replaced with new components that offer sharper bodylines and improved rider movement.
Suspension has never been a concern on the Yamaha YZF line, thanks to their use of KYB's SSS mechanical fork and shock, but even those areas saw refinement for 2019. Hidden inside the fork tube are a 25mm cylinder and piston (up 1mm from 2018), a new mid-speed valve with leaf spring, a new pressure piston, and a stiffer spring rate of 4.7N/mm (up from 4.6N/mm). On the rear, the shock body's sub tank capacity has been increased by 30cc and is paired with a new spring that is made from thinner material and features less bends in its design for reduced weight (210 grams) and a stiffer spring rate of 56N/mm (up from 54N/mm). The changes to the fork cylinder and piston plus the shock body allow for an increase in oil flow for a more controlled damping character.
On The Track
It's difficult to pinpoint what sticks out the most when riding the 2019 Yamaha YZ250F. Is it the power profile of the engine or the stiffer feel of the chassis? Both are apparent as soon as a rider gets going on the new blue bike, as together they entice a rider to push the pace and try new lines. We're pleased to say that the multiple changes made to the engine in an effort to increase mid to high did not sacrifice the low-end that the YZ250F has become known for, as the bike still pulls with power and has torque that is unmatched by other bikes in the class. But once up to speed, it's clear that the engineer's intentions were accomplished. The powerplant works best when a rider revs and stretches out every gear to the maximum and as soon as they click up on the shifter, the speeds quickly increase. Our first motos were done with a stock map setting from Yamaha programmed into the ignition and right away we could tell the bike produced more power than its predecessor. After hearing talk of a setting developed by the brand's team of testing riders (one that is said will be shared with the public), our impression of the bike was changed for the better, as the engine revved freer and felt even faster. But with that said, everyone will be able to find a setting they feel suits them best through the ignition and fuel mapping adjustments offered through the Power Tuner application.
The chassis of the 2019 YZ250F is definitely suited for faster riders, as the increased rigidity feels incredibly stiff when compared to the 2018. But this is actually a good thing, because it seems much more planted and predictable, which makes a rider more comfortable and confident as they push the pace. Straight-line stability is much improved, with no sensations of headshake or uncertainty when at speed. Yamaha's decision to greatly angle the placement of the engine in the frame for an improved center of gravity has been met with mixed opinions over the years, but this current iteration is the best used so far in the YZ250F, because the front-end does not suffer from the vague steering sensations that so many have complained about. All of these attributes are greatly aided by the KYB suspension components, which are the best that have ever graced the small-bore blue bike in stock condition. The fork and shock absorb every impact with predictability and precision, without a harsh sensation anywhere in the stroke, and the increased spring rates are perfectly matched to the stiffer sensation of the chassis. All of this, plus the ease of use through the traditional tuning tasks (no fork pumps needed here) make it clear why Yamaha never strayed from the standard spring path.
To be blunt, the body panels of Yamaha's previous machines were bulky, overly complicated to assemble, and made it difficult for a rider to move around. With that said, we're pleased to see that they've ditched the old designs for slimmer, sleeker pieces and a smoother seat that never interferes with a rider's movements. The flat and narrow compartment will appeal to riders of nearly every size and skillset, and the look is much more attractive. Most of our riders expressed no issue with the bend of Yamaha's tapered handlebar and all applauded the adjustability offered by the bar mounts.
Sometimes when a motorcycle manufacturer drags out the development of their motorcycle, we wonder what the reasons as to why might be. Do they feel that they have reached their zenith on the particular model or do they have something even better in the works that requires more time to fine-tune? After five years between major changes to the YZ250F, we're excited to say that Yamaha's delay was done to produce their best 250F yet. The new bike has an excellent engine, stellar suspension, and incredible chassis that can appeal to everyone.
2019 YAMAHA YZ250F UPDATES & FEATURES
All-new engine with electric starter, reconfigured cylinder head with new valve train, intake camshaft, higher compression piston, and Mikuni throttle body for improved mid to top performance
All-new frame design with revised geometry for increased stiffness and stability
Revised ECU settings
Updated exhaust system with new head pipe shape and rubber mounted muffler
Dual electrode sparkplug (LMAR9E-J)
New clutch with increased diameter, increased number of clutch springs, increased steel plate thickness, and reduced number of friction plates
New plastic body panels and flatter seat for improved rider movement
New fork lugs
New thinner and lighter tapered handlebars
Revised KYB suspension with updated internal parts and stiffer spring rates
Reduced capacity fuel tank
Flat air filter element
Yamaha Power Tuner smartphone application compatibility for ignition and fuel map adjustability