Credit for the current state of the 85 class should go to Yamaha, as the brand was the first major OEM to maximize the engine size rules in amateur racing when they bumped the displacement up to 85cc in the early 2000s. Knowing that bigger is always better, especially in mini bike racing, almost instantly the YZ85 became the bike of choice for competitive young riders around the country and it took a few production years for other manufacturers to follow suit. Yamaha has tinkered with various areas of the bike over the last few years, but with KTM and Husqvarna's recent releases, a full overhaul of the engine design and other improvements were deemed necessary for 2019.
Producing more power without knocking reliability is a tough task, so anytime a manufacturer talks of increased horsepower from a new engine, you know that they have spent plenty of hours and money in development. To pull more performance from the low to mid range, Yamaha went to work and redesigned nearly every component from the intake to the exhaust system. The process begins with a new airbox that funnels clean air into the Keihin PWK 28 flat-slide carburetor, but things really get interesting inside the engine, where a new crankcase with a spacer-style reed valve, longer connecting rod, new cylinder head, and Yamaha Power Valve System all work together to increase the compression of the engine to 9.6:1, produce more horesepower at a manageable rate, and work to reduce the amount that a rider will have to engage the clutch and updated six-speed transmission in order to keep the engine in the meat of the powerband. Yamaha's decision to add the YPVS to the YZ85 is important, as the spiral shaped valve that is located at the exhaust port changes the height of the port in correspondence with the engine's rpm. To make the most of the new engine, Yamaha has a new expansion chamber that optimizes the flow of fumes for improved power and added larger capacity radiators for improved cooling.
Although the center frame of the 2019 Yamaha YZ85 is the same as its predecessor, other areas of the chassis have been updated with new parts with a focus on rigidity. The most standout piece of the chassis is the new swingarm design, which is stiffer than before and offers easier maintenance of the chain via the new chain block-style adjusters. Kayba again produces the suspension components, but the diameter of the one-piece outer fork tubes have been increased to 36 millimeters and feature new internals to match while the settings of the shock have been changed to work best with the stiffer swingarm. The forks are paired to triple clamps that offer four-way adjustability, 27 millimeters of range in total, to meet the needs of young riders as they grow. An oversized tapered handlebar and adjustable levers complete the control package up top. Although the same blue colored rims as last year are used, the pieces that are put on them are new and notable, as Yamaha has switched to Dunlop's MX3S tire package and updated the brake rotors with a 220-millimeter wave front rotor and 190-millimeter wave rear rotor.
On The Track
Developing a mini bike to meet the needs of all riders is a challenge. If a brand builds a motor package that is too slow and mellow, they will lose the interest of skilled racers that need every ounce of power. But if a brand does the opposite and focuses solely on making the fastest engine possible, they will alienate the crop of riders that are transitioning up to the 85cc class or are even just learning to ride. The YZ85 has historically favored riders of a faster and more talented profile, but their intentions to make more power down low and through the middle seems to be an olive branch to the less skilled. Our test riders noticed that the engine's power profile was much easier to manage than the 2018 Yamaha YZ85 that was on hand for comparison. The low-end rolls on with no sudden spike that could startle the rider or rip the bike away, and it was easy to manage the engine without a worry that the rpms would drop too low and stall. If a rider needed a sudden spike in power out of a slow turn, a dab on the clutch would whip the engine up and helped get over awaiting obstacles. The middle of the powerband was just as impressive, as it was broad and easy to remain in. Skilled test riders noted that they could feel the benefits of the YPVS the most in the middle of the range, as the engine revved freely and put out the right amount of power without too much effort, and this carried up into the top-end over-rev, an area where the Yamaha engine has always excelled. Since this is a small-bore two-stroke, riders will still hit the clutch lever and shifter countless times over the course of a moto, but the larger cogs in the transmission made it feel like the total number of toe-taps and finger pulls was reduced by a little bit.
With faster speeds comes a need for a stiffer chassis, and Yamaha aced this area with the new suspension settings. Riders of all sizes felt that the bike was more stable at speed, especially at the front-end, but that it was not overly stiff. Just like the engine, it's difficult for a developer to make suspension that will be perfect for riders of all sizes and skill levels, but Kayaba's front fork and rear shock are very good. Both ends of the suspension soaked up obstacles on the track with ease, without the dreaded metal-to-metal clank from a jump too big or harshness anywhere in the stroke, but the base settings will not be perfect for everyone. Smaller, lighter riders might feel that the suspension is too stiff and fast, while very large and very fast riders will likely need a little firmer setting. One thing that they all agreed on was the adjustability offered by the YZ85, especially the bar mounts. The oversized tapered bar that comes stock is the typical middle of the road offering we've come to expect from Yamaha as it's not too extreme with sweep or width, so it's a good option for many and will be able to take a few good spills before being bent out of shape. It's strange to see a 220-millimeter front brake and 190 millimeter rear brake rotors come stock on a mini bike, as these were the big-bike standard for many years, but the big discs do a fantastic job bringing the bike to a controlled stop and withstand the abuse of brake draggers and long motos.
There's no denying that Yamaha's reign over the mini class was weakened in recent years, as the starting line of any amateur race feature a number orange and white bikes than ever before. But with the new 2019 Yamaha YZ85 we expect to see more riders of all skill levels, from modest beginner to SuperMini star, back on blue in the coming years The engine is well-rounded and offers a solid low-end, a broad middle, and powerful top-end that will meet the demands of a young riders, while the chassis and suspension perfectly accommodate the power package. All of this and the wide range of adjustability offered in the handlebar mounts, suspension settings, and engine modifications should make it possible for an adolescent rider to spend their entire 85 career at the controls of on machine.
2019 YAMAHA YZ85 UPDATES & FEATURES
All-new engine with new intake, crankcase, longer connecting rod, cylinder head, exhaust expansion chamber, and Yamaha Power Valve System to increase compression (9.6:1 compression ratio) and improve performance in low to mid ranges.
Increased width of transmission gears for improved engagement and smoother shifts.
High capacity radiator and cast aluminum impeller for improved cooling.
Stiffer swingarm for improved stability, along with composite chain guide and block-style chain adjusters for easier maintenance.
Updated Kayaba suspension components, with larger 36mm diameter inverted fork tubes and updated settings to the fork and shock to match stiffer chassis.
220 mm wave front rotor and 190 mm wave rear rotor for improved braking performance.
Dunlop MX3S tires on front and rear