2017 Yamaha YZ250F
For 2017, Yamaha has taken the 250F with arguably the best engine in the class and taken it another step. With a total of 18 changes to the new YZ250F, the focus was to take what they've learned from Star Racing, with Cooper Webb and Jeremy Martin, then put this all to work for the general consumer. The largest of these changes is the continued development of the down-draft intake design, which Yamaha utilizes through their use of the reverse cylinder. The near vertical intake tract has had its angle decreased even further for 2017, meaning the air and fuel has an even straighter shot as it enters and passes through the cylinder head. This also includes changing the intake ports to further improve this flow, along with the exhaust port and exhaust mid-pipe to allow for the gasses to escape more efficiently after the combustion cycle. With this added power, Yamaha also beefed up some of the bottom-end components, such as the rod and transmissions parts, to aid in keeping the reliability that's needed.
Beyond this, the YZ250F also receives the same chassis adjustments that the YZ450F gained in 2016. The main frame has more material along the bottom of the spars, near the footpeg region; they've also lowered the footpegs five millimeters, along with changing the thickness and material used for the engine mounts. Even though Yamaha is widely praised for their continued use of KYB's SSS spring forks, there were still some updates on both the front and rear when it comes to suspension. The front forks have new settings, along with a .1 newton meter lower rate fork spring. Out back, KYB's shock retains the same spring as 2016 but receives an updated setting as well.
For a deeper look into the changes for 2017, check here - First Look: 2017 Yamaha YZ250F.