2020 Yamaha YZ125X

First Impression: 2020 Yamaha YZ125X
More two-strokes! This cross-country premixin’ 125 is light, agile, and just plain fun to rip down the tightest single track you can find.

Premix fanatics unite! Ok, we know it isn’t a new two-stroke motocross machine but another two-stroke option is still a good thing. And when it comes down to it, cross-country style racing is still a growing sector of the dirt bike market and off-road is where a majority of riders, including pro motocrossers, get their start. 

Speaking of starting, that is exactly what the YZ125X is aimed at. Getting people started in the glorious sport that is dirt bike riding. Or even getting them riding again for those older guys and gals who want to get back into it. Yamaha explained that the 125X is the perfect bike for the young teen who isn’t quite ready for a 250FX or for an adult rider who’s possibly outgrowing a play/trail bike like a TT-R230. 

What’s Different Than Moto?

Obviously, the YZ125X is based on the YZ125 and the two machines share a vast majority of features. They both have the same frame, tank, bodywork, seat, swingarm, transmission, cylinder, clamps, bars, and other small things. But, what sets the X apart is what Yamaha calls GNCC-style features that are aimed at making the bike a better cross-country racing weapon. This is still a competition model developed with getting wins in mind. 


Starting with the changes to the suspension, you should be happy to know that the YZ125X still has the base coil spring KYB SSS Fork and the KYB shock that is on all YZ models. But, they did change the internal valve shim stacks to lower the damping in both the fork and shock, yet they maintain the same spring rates as the moto YZ125 (4.1 N/mm in front and 46 N/mm out back). 


While the transmission and cylinder are the same, the YZ125X has an all-new cylinder head. The new head features a larger combustion chamber volume, higher combustion chamber height, and lower compression ratio. The YPVS (Yamaha Power Valve System) is also changed with a stiffer spring and different exhaust port shape that delays the opening of the valve and slows the rate at which it opens. Ignition timing has also been advanced five degrees at low-to-mid RPM and slightly delayed at high RPMs. Lastly, carburetor changes have been made to match up with the new head and timing. 

Off-Road Extras

To make it a better off-roader, the YZ125X gets an 18-inch rear wheel with a wider rim (2.12x18), Dunlop AT81 tires, a 50 tooth rear sprocket (up from 48), an O-ring chain, aluminum kickstand, and reserve fuel petcock. All of these “add-ons” are pretty much what any off-road rider would need to add to a YZ125 to make it ready for the trails. 

On the Trail


The biggest difference that I felt on the trail was the power. Out of all the motocross 125 bikes that I’ve ridden, (TM, KTM, Husqvarna, and Yamaha) the YZ125 has the broadest spread of power and easiest to ride, as far as small two-strokes go, and the YZ250FX goes even further in that direction. Yet, it probably doesn’t have the most peak ponies as the other bikes. When we first hit the trails on the 125X, peak horsepower was the last thing on my mind - we were hit with icy, slick, muddy, tight single track that demanded every ounce of traction a bike and rider could muster. And the YZ125X’s power was just what was needed.

The power on the X is even more spread out and linear than the moto YZ125, which lets you lug second gear where you would never dream of trying on a regular 125. Obviously, the motor on the X is not a torque monster (the saying still applies, “no replacement for displacement”) but the changes to the engine shifted the meat of the power low enough that I could confidently ride in second gear through tree-dodging S-turns and 180s and not have to abuse the clutch. The bike sounded like it was going to bog and not make power, but it just kept chugging along and could get me through trails much more smoothly than shifting between first and second gear on peaky-powered 125.

I can’t even really say that the mid-range was lacking. It didn’t feel milder than moto 125, but the power is definitely more four-stroke like and linear, which makes for less of a hit in the mid. All that being said, you do have to shift a lot more than a 250F and you also have to be very aware of what gear you are in. Surprise hills or ledges right after a blind turn will catch you off guard and if you are cruising in third, you need to quickly downshift and give it the beans. 


This might be the most comfortable suspension I’ve ever ridden, bordering on too soft even for the super-tight sections of the trail. I’m heavier than the target rider (215 lb) so this isn’t a surprise. But, with the sag set for me, the bike was balanced and extremely planted to the ground. I could predict exactly what the front and rear wheels were going to do through ruts, over logs, up hills, across roots, and so on. There is a maximum amount of plushness, and yet the bike still had pretty good bottoming resistance. It feels as though the suspension matches the power of the bike really well. 

On the flip side, this is the only “X” in the lineup that I don’t think would be any fun on the motocross track, because of the suspension. There was a track on the property we rode but it was too muddy to really do any motos. Yet when the trails opened up and got a lot faster, the suspension was pushed to its limit and I couldn’t slam into anything at high speeds. 


There is nothing easier to handle in the woods than a 125. The 125X is so light and agile that I really didn’t have any issues clipping trees or navigating the serpentine trail network. The light weight also makes it have a “float over” feeling rather than a “slam through” feeling when it comes to rough terrain. That is, as long as the hits don’t get too big. This bike was magic at whipping through the trees and chewing up roots, holes, and trail chop. We spend a lot of time on four-strokes and it is easy to forget that two-strokes have so much less rotating mass and need much less rider input to get them to turn and change direction. Plus, picking up the bike (which I did a number of times) and getting going again isn’t that big a deal. 


The wider rear tire (110/90-18) is a definite help in softer terrain and was appreciated in both the deeper sandy sections, loose mulchyness, and the slick red clay. Not that starting any 125 is hard, but with less compression, the YZ125X is crazy easy to start, which helps when you stall balancing in a precarious position. Lastly, even though the exhaust system is the same as the YZ, the X seems quieter and in the woods, we could barely hear the other Xs riding around while it was very obvious when a four-stroke was within a mile of us. 


We have to split some hairs to come up negatives on this bike, but we have a few to mention. One, no e-start. And yes, I know that is a bit hypocritical when I just said how light and easy to start the bike is. Adding the magic button would add weight, but would also be convenient. Two, the X doesn’t have any bike protection - handguards and a skid plate would be nice. And thirdly, as an “X” model (not a WR) I’d expect the YZ125X to be a little more moto-able. Compared to the YZ250FX, YZ450FX, and YZ250X, the 125X has a much softer suspension setting that would make even a vet track a little sketchy. 


On the track or the trail, 125s are an absolute blast to ride. You always feel like a hero, you can slice through the tightest trails with ease and you can ride them all day without getting worn out too fast. The YZ125X truly slots into Yamaha’s bike line up as a stepping stone from the small two-strokes or TT-R line into off-road competition, or just trail riding. While the bike takes less physical strength and stamina to ride fast, it does require a degree of mental acuity that isn’t necessary on big ol’ four-strokes. You can’t be lazy, make poor line choices, and not carry momentum just to be saved by massive power. The YZ125X surprised us with it’s climbing ability, but it takes more skill from you. And to be honest that is just what a young ripper needs - a bike that he or she can control, feel confident on, and build vital riding skills that will always be useful on any bike.


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Yamaha YZ125X
Model Year
Engine Size
Engine Type
Engine Displacement
125cc liquid-cooled 2-stroke; reed-valve inducted
Bore x Stroke
54.0 mm x 54.5 mm
Compression Ratio
Fuel System
6-speed; multiplate wet clutch
Final Drive
Suspension Front
KYB® spring-type fork with speed sensitive damping; fully adjustable, 11.8-in travel
Suspension Rear
KYB® single shock; fully adjustable, 12.4-in travel
Brakes Front
Hydraulic disc, 270mm
Brakes Rear
Hydraulic disc, 245mm
Tires Front
90/90-21 Dunlop® AT81F
Tires Rear
110/90-18 Dunlop® AT81
Overall Length
84.3 in
Overall Width
32.5 in
Overall Height
50.6 in
Seat Height
37.6 in
57.3 in
Ground Clearance
13.8 in
Fuel Capacity
2.1 gal
Curb Weight
209 lb
More Info
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