2017 Yamaha YZ125: Brake Upgrade & Enduring Legacy

The world of motocross is constantly evolving, with manufacturers pushing the boundaries of technology and performance. Yet, some models hold a special place in the hearts of riders, even when their updates are few and far between. The 2017 Yamaha YZ125 is one such machine, a revered two-stroke that, despite a long history of subtle refinements, brought one particularly noteworthy enhancement to the fore. Enthusiasts and prospective owners alike are often keen to know: does the 2017 Yamaha YZ125 truly feature a new brake rotor, and what impact does this, and its other minor tweaks, have on its performance?

Indeed, for 2017, the Yamaha YZ125 received a significant upgrade in its stopping power. Yamaha equipped the YZ125 with an improved front brake system, featuring a larger 270mm front rotor, a considerable step up from its previous 250mm old-school counterpart. This enhancement wasn't just about size; it also included different, more effective front brake pads. Remarkably, these are the very same rotor and pads found on Yamaha's more powerful YZ250F and YZ450F four-stroke models, signalling a serious commitment to enhancing braking performance. Beyond this crucial braking improvement, the 2017 model's changes were largely limited to its Bold New Graphics (BNG), a common refresh for models with long production runs. So, while the visual changes were minimal, the functional upgrade to the brakes offers a tangible benefit to riders seeking better control and confidence on the track.

A Look Back: The YZ125's Evolutionary Journey

For over a decade, the Yamaha YZ125 has maintained a largely consistent performance and handling profile. While some might view this as stagnation, Yamaha has, in fact, made numerous targeted changes over the years, even if radical overhauls have been scarce. These modifications often aimed to align the YZ125 more closely with its four-stroke siblings or to conform to worldwide specifications, making it a truly global model. The fact that Yamaha remains one of the last Japanese manufacturers to produce 125cc and 250cc two-stroke motocross bikes is a testament to its enduring appeal and a point of gratitude for many two-stroke aficionados.

The Foundation: 2005 YZ125 Innovations

The 2005 YZ125 serves as the fundamental blueprint for the 2017 model. This year marked a significant overhaul, particularly for the engine, which was virtually all new, sharing only the kickstarter and clutch plates with its 2004 predecessor. Yamaha introduced a smaller, lighter, and faster engine, moving from a domed 2004 piston to a flat-top design. The connecting rod was shortened by 3mm, and the exhaust port was raised by 0.5mm. To straighten the intake tract, the engine was tilted forward 7.5 degrees, reducing the off-centre angle from 16 to 5 degrees. Other engine refinements included changes to the coolant port and a plastic water-pump impeller with a 4mm smaller drive shaft. The clutch actuator arm was relocated, and the transmission was upgraded from five to six speeds. Even the exhaust pipe received a straighter initial section.

Beyond the engine, 2005 was pivotal for the chassis. Yamaha transitioned from its traditional steel frame to an innovative plug-and-play aluminium frame, a design that remains largely consistent with the 2017 model. This new frame, devoid of round tubes and instead utilising forgings, castings, and extrusions, was a remarkable 4-1/2 pounds lighter than the 2004 steel frame. The bike's overall weight dropped to 197 pounds. It also adopted Honda-style brake routing and, for the first time, 7/8-inch Renthal aluminium handlebars. The Kayaba forks of this era, affectionately dubbed "Showabas" by some, were advanced copies of Showa’s Twin Chamber forks, featuring dual chambers, top-mounted compression adjusters, and one-piece outer tubes.

Defining Moments: 2006 SSS Suspension and Beyond

The 2006 YZ125 brought further engine refinements, including changes to the combustion chamber’s squish band, carburetor, a stiffer power-valve governor spring (opening at 9500 rpm instead of 9000 rpm), new CDI mapping, and an NGK BR9EVX platinum-alloy plug. However, the most profound change that year, one that continues to define Yamaha models, was the adoption of Kayaba SSS (Speed Sensitive System) suspension components. This revolutionary system shifted Yamaha’s suspension from 30-percent speed-sensitive damping to an astonishing 90-percent speed-sensitive, offering unparalleled performance. The rear shock was equally impressive, featuring an 18mm shaft (up from 16mm), Kashima-coated internals, a 30-percent-larger reservoir, and a titanium shock spring—a setup remarkably close to a factory-level works shock.

Additional 2006 updates included adjustable handlebar mounts, a sleeker front-brake lever, an on-the-fly quick-adjust clutch lever, wider fork-tube spacing, a low-profile rear-brake caliper with new pad material, plastic rear-brake caliper and rotor guards, a softer and taller saddle, a new front number-plate shape, and a Dunlop D756 rear tyre, replacing the 2005’s D739, though the front remained a D739.

Subsequent Years: Incremental Refinements

• 2007 YZ125: Five key changes, including tapered fork stanchion tubes with new damping, lighter aluminium components in the Kayaba shock, a switch to 1-1/8-inch Pro Taper Contour bars, aluminium bolts replacing steel counterparts across various parts, and a shortened silencer perf-core section for improved throttle response without increasing sound.
• 2008 YZ125: Eight changes aimed at closer compliance with the YZ250F, adopting its front-brake caliper, fork stanchions, lower fork bracket, and chain guide. A new reed valve was added, and the front master cylinder piston was made smaller, with the brake lever repositioned.
• 2009 YZ125: Four changes, including a lighter aluminium brake-hose holder, a special zinc coating for the chain, a woven seat cover, and a switch to a Dunlop 742F front tyre.
• 2010 YZ125: Bold New Graphics (BNG).
• 2011 YZ125: Changes to conform to a worldwide global spec for cost efficiency, including a 75mm-longer silencer with an increased core and more glass-wool packing. The main jet was changed from 410 to 430, and the needle from 6BFY42-3 to 6BFY43-3.
• 2012 YZ125: BNG.
• 2013 YZ125: A white rear fender and BNG.
• 2014 YZ125: BNG.
• 2015 YZ125: Received bigger footpegs, Dunlop MX52 tyres, the latest-generation KYB Speed-Sensitive fork, and a new airbox. However, the most significant updates were cosmetic, giving the YZ125 a much-needed facelift.
• 2016 YZ125: Black rims, a gold chain, and BNG.

2017 Yamaha YZ125 vs. 2017 KTM 125SX: The Austrian Challenge

While the 2017 YZ125's new brake rotor is a commendable improvement, the landscape of the 125cc two-stroke class has shifted dramatically, largely due to the formidable presence of KTM. The 2017 KTM 125SX, equipped with its highly effective AER air forks (a vast improvement over the previous year's problematic 4CS suspension), presents a significant challenge. KTM's combination of superb forks, a robust hydraulic clutch, well-modulated Brembo brakes, modern aesthetics, and superior handling truly sets it apart, leaving the long-standing YZ125 somewhat overshadowed.

Despite this, the YZ125's Kayaba SSS components remain a strong point, widely regarded as some of the best production suspension available. However, the overall package of the KTM 125SX, and its clone-like sibling, the Husqvarna TC125, offers a more contemporary and competitive edge straight out of the showroom.

Bridging the Gap: Making the YZ125 Competitive

Can the YZ125 still compete with the KTM 125SX? Absolutely, but it requires an investment. While the 2017 YZ125 saw a slight price increase, it remains approximately £300-£400 cheaper than the KTM 125SX and £400-£500 less than the Husky TC125. This price difference can be channelled into aftermarket upgrades to significantly boost its performance. Here are some suggestions:

Recommended Hop-Up Parts:

It's important to note that while these modifications can significantly improve the YZ125, the initial cost saving compared to a KTM 125SX can quickly diminish once upgrades are factored in. Many hardcore YZ125 racers opt for used models and rebuild the engines for a fraction of the cost of a new bike, highlighting the bike's rebuildability and the perceived lack of motivation to buy new when major updates are absent.

What We Liked and Disliked About the 2017 YZ125

What We Disliked:

• Chassis: While light and well-suspended, the YZ125's decade-old frame architecture gives up considerable ground to KTM’s modern steel frame in terms of handling and feel.
• Engine: To keep it in the optimal powerband, the clutch often needs to be aggressively used. While aftermarket power is available, it adds to the overall cost.
• Front Tyre: The standard Dunlop MX52 front tyre is often seen as less-than-stellar, making the front end feel less precise than it could be. Upgrading to a Dunlop MX3S can offer significant improvements in most conditions, though it may wear faster.
• Powerband: While enjoyable, a little more bottom-end grunt would reduce the reliance on constant clutch engagement.
• Price & New Sales: Despite being the lowest-priced bike in its class, the lack of drastic updates means many riders opt for used models, rebuilding them cheaply. This diminishes the incentive to purchase a new YZ125.

What We Liked:

• Clutch: Despite needing frequent use, the clutch is incredibly durable and handles abuse like a champion.
• Suspension: The Kayaba SSS (Speed Sensitive System) components are universally praised as some of the best production suspension available, performing exceptionally well for riders of all skill levels and sizes.
• Maintenance: The YZ125 is renowned for its ease of maintenance. A top-end rebuild is straightforward and incredibly affordable, with piston kits costing significantly less than those for four-stroke models.
• Bulletproof Durability: Yamaha has an excellent reputation for long-lasting reliability, making the YZ125 a dependable choice.
• Weight: At under 200 pounds (194 lbs for the 2017 model), the Yamaha YZ125 is exceptionally light, making it easy to ride, agile, and forgiving.

Our Verdict on the 2017 Yamaha YZ125

For decades, the Yamaha YZ125 has been a beloved icon, a machine that was truly ahead of its time upon its initial introduction. It consistently dominated 125cc shootouts, cementing its legend. However, the motocross landscape has evolved dramatically. While the 2017 model's new 270mm front brake rotor is a welcome, practical improvement, it cannot mask the fact that the YZ125 is now largely outclassed by the relentless innovation of the Austrian manufacturers, particularly KTM. The 2017 KTM 125SX, with its comprehensive package of modern technology and performance, is, by most metrics, a superior machine. Twelve years ago, the tables were turned. Today, there's a new benchmark. For the YZ125 to reclaim its former glory, Yamaha would need to implement drastic, performance-oriented updates that go far beyond Bold New Graphics and incremental improvements.

2017 Yamaha YZ125 Setup Specifications

For those looking to fine-tune their 2017 Yamaha YZ125, here are recommended setup specifications based on extensive testing, intended as a guide to help you find your ideal settings:

Kayaba SSS Fork Settings:

• Spring Rate: 0.42 kg/mm
• Compression: 12 clicks out (from fully stiff)
• Rebound: 12 clicks out (from fully stiff)
• Fork-Leg Height: 5mm up (in the triple clamps)

Notes: These are truly exceptional forks, further enhanced by the two-stroke engine's light feel and snappy input. For faster or heavier riders, a stiffer fork spring might be considered. However, many skilled riders can effectively use the stock springs by dialling in more compression and leveraging the crossover effect of rebound damping.

Kayaba SSS Shock Settings:

• Spring Rate: 4.7 kg/mm
• Race Sag: 100mm (measured from the rear axle to a fixed point on the rear fender, with the rider in full gear)
• Hi-Compression: 1-1/2 turns out (from fully stiff)
• Lo-Compression: 12 clicks out (from fully stiff)
• Rebound: 12 clicks out (from fully stiff)

Notes: This shock performs flawlessly, tracking straight and remaining perfectly in tune with the bike's chassis. Its consistent and predictable behaviour makes it a standout component.

Yamaha YZ125 Jetting Specifications:

Yamaha has meticulously refined its jetting over the years, ensuring the 2017 YZ125 runs exceptionally clean straight from the factory. The following specifications are for the 38mm Mikuni TMX carburettor:

• Main Jet: 430
• Pilot Jet: 40
• Needle: 6BFY43-3
• Clip Position: 3rd from top
• Air Screw: 2-1/4 turns out (from fully seated)

Notes: Yamaha thoughtfully includes one richer (440) and one leaner (420) main jet with the bike, allowing for environmental adjustments. The current 6BFY43-3 needle is a half-clip richer than the older 6BFY42-3 needle used before the global spec standardisation. If you undertake engine porting or install an aftermarket exhaust system, it's advisable to consider moving up to the 440 main jet. For an added layer of safety and performance, especially with significant engine modifications, adding a splash of VP C-12 racing fuel to every 5 gallons of petrol can be beneficial.

Frequently Asked Questions (FAQs)

Q: Is the 2017 Yamaha YZ125 better than the 2016 YZ125?
A: Yes, primarily due to its improved braking system. The 2017 model features a larger 270mm front rotor and new brake pads, offering significantly better stopping power than the 2016 model's 250mm rotor. Other changes were limited to Bold New Graphics (BNG).

Q: What was the most significant update to the 2017 YZ125?
A: The most significant functional update was the new 270mm front disc brake, along with new brake pad material. This brings the YZ125's braking performance into a more modern and competitive realm.

Q: Does the 2017 YZ125 have the same engine as previous years?
A: The core engine design for the 2017 YZ125 largely stems from the all-new engine introduced in the 2005 model, with minor refinements made in subsequent years. There were no major engine overhauls for the 2017 model year.

Q: How does the YZ125's suspension compare to other bikes?
A: The Kayaba SSS (Speed Sensitive System) suspension components on the YZ125 are widely regarded as some of the best production suspension available, offering excellent performance for a wide range of riders.

Q: Is the 2017 YZ125 competitive against the 2017 KTM 125SX?
A: Out of the box, the 2017 KTM 125SX generally offers a more competitive package, particularly with its superior AER air forks, hydraulic clutch, and Brembo brakes. However, with strategic aftermarket modifications, the YZ125 can be made highly competitive.

Q: What is the weight of the 2017 Yamaha YZ125?
A: The 2017 YZ125 weighs 194 pounds, making it a very light and agile machine.

Q: What are the main advantages of owning a YZ125?
A: Key advantages include its exceptional Kayaba SSS suspension, renowned reliability and durability, ease and affordability of maintenance (especially top-end rebuilds), and its light, agile handling due to its low weight.

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