YZ 125 Top Speed: How Fast Is It?

Are you wondering what the YZ 125 top speed is? Pretty much anyone who owns a dirt bike, car, truck, or really any vehicle, wants to know how fast it goes. In this case, how fast is a yz125?

I recently bought a 2023 YZ125, so I know I wanted to know how fast it went.

What is a YZ 125 top speed?

Yamaha has improved the YZ125 over the years, and the top speed varies slightly depending on the model and year of production.

For example, a 2019 YZ125 has a top speed of around 60 miles per hour, while the 2021 YZ125 is said to be able to reach up to 65-70 miles per hour. 

A 2000 YZ125 top speed is similar to the 2019, around 55-60 miles per hour, which remained unchanged in the following decade. Yamaha didn’t make many changes to the YZ125 between 2000 and 2021. In 2022, they made a big change.

You can see how this compares to Yamaha’s four-stroke 125, the TTR 125 here (learn the difference between the YZ 125 and the Yamaha TTR 125), Honda’s CRF150R, or the YZ125’s cousins: the YZ250 and YZ85.

Several factors impact how fast a YZ125 is, but there are also ways to improve this bike’s top speed by adding mods and upgrades.

What Impacts the YZ 125 Top Speed

It can be tough to calculate the true top speed of a dirt bike because there are quite a few different items that can impact it. Let’s take a look at them.

Engine Work and Aftermarket Parts

This might be obvious to some, but engine work and aftermarket parts are going to impact the YZ125 top speed. Arguably, most of anything.

If your YZ125 has engine work (especially a big bore kit, like the popular 144cc big bore kit) and a pipe, that’s not really comparable to the top speed of a stock YZ125.

The speed of a YZ125 that hasn’t had any work done to it will be significantly lower than the top speed of a YZ125 that has undergone a lot of mods.

The more work you do to the bike, the greater the difference in speeds will be. You spent a bunch of money on the aftermarket parts to make it faster, didn’t you?

Also, the beating heart of the YZ125 is a 2-stroke engine. The two-stroke engine has only two phases: compression and combustion.

Lubrication is not the same as a four-stroke engine since oil is mixed with fuel directly into the combustion chamber, lubricating the piston.

A similar size engine (125cc) in a 4-stroke, such as a Kayo dirt bike or XPro dirt bike, will not go nearly as fast as the YZ 125 top speed. This is partially due to the Kayo dirt bike and XPro dirt bike being Chinese rather than Japanese like the YZ125 and because those motors are horizontal versus vertical, but 4-stroke versus 2-stroke also plays a big role in the top speed of the bikes.

There are other factors at play here too – such as gearing, riding conditions, and more.

Gearing

The second most important factor in determining the YZ125 top speed is its gearing. Gearing refers to the size (and ratio) of the front and rear sprockets.

For reference, the stock gearing for this bike is a 13-tooth front sprocket and a 49-tooth rear sprocket (depending on the year of your bike).

Riders normally pick different gearing depending on the situation they’re riding. If the rider is racing a tight, technical track, they would typically want more acceleration (also referred to as more bottom end). To achieve this, they’d use either a smaller front sprocket or a larger rear one. This is known as having a low gear ratio.

If the rider is racing a motocross-style track, they may want more top speed (known as top end). To do this, the rider would use a larger front sprocket or a smaller rear sprocket; in other words, they would be changing to a higher gear ratio.

Riding in the woods can require an entirely different gearing combination than both of those.

This might not sound like much to some people, but it has a large impact on the top speed of any dirt bike, including the YZ125. It not only impacts how fast the bike can go, but also where the bike makes its power.

A YZ125 with a 6-tooth front sprocket will have a different top speed and make power differently than one with the stock 14-tooth front sprocket (I made the difference wide to make a point — no one is running a 6-tooth front sprocket on their YZ125….).

Additionally, a change to the front sprocket has a greater effect on a dirt bike than changing the rear sprocket. Going up or down one tooth on the front sprocket is not equal to one tooth on the rear sprocket.

Rather, changing the front sprocket by one tooth is equivalent to 3-4 teeth in the rear.

Rider: Size and Ability

The top speed of a YZ125 is going to be slower if the rider weighs more because it takes more work from the bike, while the bike and engine maintain the same ability/capacity. The heavier the rider, generally the lower the YZ 125 top speed is going to be.

In addition, an experienced rider can make the YZ125 go faster than a beginner who is just learning. A rider who knows how to quickly and smoothly shift gears can hit a higher top speed than someone who is just learning how to use a clutch.

Conditions of Riding

The YZ 125 top speed can also be impacted by riding conditions, including both location and surface.

For example, a dirt bike’s power output is generally higher closer to sea level than at high altitudes. So if you’re planning to ride your YZ125 in the mountains, it will likely have a lower top speed than if you were riding at sea level.

Or, even if you’re not in the mountains necessarily, but you’re just riding in Colorado, you’re much higher above sea level than the coasts of the US. That will cause your dirt bike to be slower.

Smaller-size bikes (bikes with small cc engines) are more impacted by elevation changes than larger bikes, too. For example, a 125cc bike is more impacted than a 450.

How about the conditions you’re actually riding on or in?

Are you riding in the woods, on a motocross track, or on a paved road? If it’s in the woods, your top speed might be limited. If you’re racing motocross, you can only go so fast while remaining safe and within bounds (and, don’t forget, sometimes slow is fast).

Apart from the elevation and location, another factor that affects the KX100 top speed is the surface on which it is being ridden. A bike ridden on flat pavement will be different than if it were driven on a tight, sandy motocross course; even the type of tires can make a difference.

A Few Other Factors that Can Impact the YZ125 Top Speed

Your YZ125 top speed can also be impacted by a few more things, including the condition of your bike, the weather, and how you’re recording the data.

A bike that is regularly maintained will run faster and more efficiently than one that isn’t. For example, a YZ125 that has had consistent maintenance done to it will be able to reach a higher top speed than one not taken care of properly.

The weather and temperature can both affect your YZ125 top speed. If it rains, the pavement will be wet, or the track and woods may be muddy, and your top speed will probably be lower than normal. Similarly, if it’s an abnormally cold or hot day, that could impact how well the bike is running, which could then lower the top speed.

If you want to get an accurate reading of the top speed of a YZ125, use a high-quality onboard GPS device rather than relying on someone pointing a speed gauge at you as you zoom past. This doesn’t mean the bike will actually go any faster or slower, it just changes what you end up seeing on paper.

Ultimately, most people want to know their bike’s rough top speed. Yes, mods and other items impact a YZ125 top speed potential, but at the end of the day, people just want to have an idea of how fast their bike is.

With that in mind, a YZ125 top speed is about 65-70 mph.

YZ125 Top Speed Video

Frequently Asked Questions About the YZ 125 Top Speed