07/05/2006
Yamaha YZ85: A Comprehensive Overview
The Yamaha YZ85 has long been a staple in the competitive world of mini-motocross, a proving ground for the next generation of racing talent. For years, this 85cc two-stroke machine remained largely unchanged, a testament to its enduring, albeit aging, design. However, a significant shift occurred with the introduction of the 2019 model, bringing a host of updates aimed at revitalising its performance and competitiveness. Further refinements followed in 2022, solidifying Yamaha's commitment to this crucial segment of the market. This article delves into the intricacies of the YZ85 engine and its overall evolution, exploring what makes this bike a compelling choice for young riders.
The 2019 YZ85: A Major Overhaul
The 2019 Yamaha YZ85 represented a substantial departure from its predecessors, which had, for the most part, remained identical to the 2002 model. This 16-year stagnation meant the YZ85 was falling behind its rivals in terms of performance. Yamaha finally addressed this by implementing a series of key updates:
Engine Enhancements: The Heart of the Update
The most significant changes were concentrated in the engine, designed to broaden the powerband and improve overall tractability:
- YPVS (Yamaha Power Valve System): This was arguably the most crucial addition. The YPVS is a dual-valve mechanical system that dynamically alters the exhaust port timing. It begins to open at 8500 rpm and is fully open by 9000 rpm. This system significantly impacts the compression ratio: when closed, it's a much higher 9.6:1 compared to the previous 8.1:1, and when fully open, it increases to 8.2:1.
- Bottom End Modifications: The crankcase shape was revised to optimise charge flow and contribute to the increased compression. The crankshaft assembly also received an update with a 4mm-shorter connecting rod and a resin weight for improved balancing.
- Top End Improvements: The cylinder now features a new combustion chamber shape, specifically designed to work in harmony with the new Power Valve system.
- Reed Block: Yamaha adopted a spacer-style reed block with 0.1mm-thicker reed pedals, aimed at improving fuel-air mixture delivery.
- CDI Box: The mapping within the CDI box was recalibrated to complement the updated engine characteristics.
- Water Pump: Both the water pump housing and the exit pipe were redesigned for improved cooling efficiency.
- Exhaust Pipe: The exhaust pipe dimensions were revised for 2019 to better suit the new engine configuration.
Chassis and Component Updates
Beyond the engine, several other components received attention:
- Transmission: Third and fourth gears were widened at the base to enhance strength and ensure smoother gear changes.
- Suspension: The 36mm KYB spring forks received a more rigid outer tube and updated settings. The shock body, while carrying over, was re-valved with different settings.
- Swingarm: A new, stiffer swingarm was introduced, featuring a revised chain guide and an updated chain adjuster system.
- Brakes: The front brake hose routing was made more direct. Both front and rear brake rotors adopted a wave-style design. The rear rotor was changed to a solid disc, intended to improve heat dissipation.
- Ergonomics and Adjustability: Yamaha aimed to make the YZ85 more adaptable to different rider sizes. This included four-position adjustable bar mounts and adjustable-reach clutch and brake levers.
Performance Impact of the 2019 Updates
The 2019 YZ85 engine, despite not producing more peak horsepower or torque than its predecessor, offered a significantly more usable and enjoyable power delivery. The key improvement was the broader powerband, making the bike more responsive from low to mid-range. The older engine was known for its abrupt power hit and quick fade, often requiring constant clutch work to stay in the narrow powerband. The 2019 model smoothed out this delivery, providing a more linear and predictable surge of power. This made it easier for less experienced riders to manage and more efficient for faster riders to exploit.
While the 2019 YZ85 boasted a more competitive engine, it still faced challenges. The gearing was considered by some test riders to be too close, leading to a feeling of being between gears. Furthermore, the engine tended to fall off revs slightly sooner than the previous model, a characteristic Yamaha attempted to mitigate with taller gearing (a 46-tooth rear sprocket instead of a 47-tooth).
Handling and Ergonomics
The chassis updates, including the stiffer swingarm and revised suspension settings, contributed to improved handling. However, a recurring issue for some riders was head-shake at higher speeds. While the bike offered impressive turn-in capabilities, stability at pace was a point of concern. The suspension, particularly the KYB components, was generally praised for its performance across a range of rider sizes.
The 2022 YZ85: Modernisation Continues
The 2022 model year saw further updates, largely inspired by Yamaha's larger two-stroke motocross bikes, the YZ125 and YZ250. These changes focused on modernising the aesthetics and improving the chassis's rigidity and rider interface:
Key 2022 Updates
- Bodywork: Radiator shrouds, fuel tank, side panels, and fenders were all redesigned to create a more modern, symmetrical, and sleeker appearance.
- Seat: The seat became flatter, taller in the middle, and narrower, with a revised mounting system for easier installation.
- Subframe: A switch from steel to an aluminium subframe reduced weight and allowed for a straighter intake tract.
- Intake: The new subframe, side panels, and seat design facilitated larger intake vents at the rear of the seat, promoting smoother and straighter airflow to the engine for improved power. A new air filter was also introduced.
- Swingarm: The swingarm was redesigned into a one-piece, cast unit, replacing the previous three-piece construction for increased strength.
- Rear Axle: The rear axle transitioned from hollow to solid for enhanced strength and rear-wheel traction, with a larger wrench head size (19mm from 17mm).
- Brakes: The rear brake master cylinder was updated with an integrated fluid reservoir, requiring less pedal travel.
The YZ85LW (Large Wheel) Option
Yamaha also introduced the YZ85LW, a big-wheel variant, mirroring a trend seen in European racing. This version features a 19-inch front and 16-inch rear wheel, a longer swingarm, and stiffer suspension settings. This option caters to larger riders or those competing in Supermini classes, offering improved stability and capability over rough terrain.
Comparative Analysis: YZ85 vs. Competition
When comparing the YZ85 to its key competitors like the KTM 85SX and Kawasaki KX85, several distinctions emerge:
| Feature | Yamaha YZ85 (2022) | KTM 85SX (2022) | Kawasaki KX85 (2022) |
|---|---|---|---|
| Price (approx.) | $4799 | $6399 | $4699 |
| Front Forks | KYB SSS (Spring, Comp/Rebound Adj.) | WP XACT (Air, Comp/Rebound Adj.) | (Spring, Comp Adj. Only) |
| Rear Shock | KYB (Low-Speed Comp/Rebound Adj.) | WP (High & Low-Speed Comp/Rebound Adj.) | (Low-Speed Comp/Rebound Adj.) |
| Handlebars | 1-1/8" Aluminium | 1-1/8" Aluminium | 7/8" Steel |
| Seat Height | 33" | 34" | 32.7" |
| Carburetor | 28mm Keihin PWK | 38mm Mikuni TMX | 28mm Keihin PWK |
| Engine Competitiveness | Good, improved from 2019 | Generally considered top-tier | Solid, but often outgunned by KTM |
The YZ85 offers a strong value proposition, particularly when compared to the KTM. While the KTM often leads in outright performance, especially with its advanced WP suspension and larger carburetor, the Yamaha provides a more accessible entry point. The Kawasaki KX85 remains a competitive option, often positioned as the most budget-friendly Japanese competitor.
Frequently Asked Questions
Q: What is the main advantage of the 2019 YZ85 engine update?
A: The addition of the YPVS (Yamaha Power Valve System) significantly broadened the powerband, making the engine more responsive and easier to ride from low to mid-range, unlike the previous abrupt power delivery.
Q: Is the 2022 YZ85 a completely new engine?
A: No, the 2022 YZ85 retains the engine configuration introduced in 2019. However, updates to the intake tract improve air delivery efficiency, leading to better throttle response.
Q: What is the YZ85LW?
A: The YZ85LW (Large Wheel) is a variant of the standard YZ85 featuring larger front (19-inch) and rear (16-inch) wheels, a longer swingarm, and firmer suspension settings. It's designed for bigger riders or those competing in Supermini classes.
Q: What are the common complaints about the YZ85?
A: Common criticisms have included head-shake at speed, gearing that feels too close, fork lugs that can drag in ruts, and in older models, an abrupt and difficult-to-manage powerband. The 2022 model has addressed some of these through chassis and component updates.
Q: How does the YZ85 suspension compare to its competitors?
A: Yamaha's KYB SSS (Speed Sensitive System) forks are highly regarded and offer both compression and rebound adjustability, providing a strong baseline for tuning. While the KTM's WP air forks offer advanced technology, the KYB units on the Yamaha are often praised for their plushness and ease of setup for a wide range of riders.
Conclusion
Yamaha has demonstrated a commitment to keeping the YZ85 relevant and competitive. The 2019 overhaul marked a significant leap forward, addressing the long-standing need for a more modern and tractable engine. The 2022 updates further refined the package, enhancing its aesthetics, ergonomics, and chassis stability. While it may not always boast the outright power of some European rivals, the YZ85 offers a compelling blend of performance, reliability, and value, making it an excellent platform for aspiring motocross racers to develop their skills.
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