Every dirt bike rider always wants to go faster.
But not every dirt bike rider can pull the Gs a 450 ride delivers and for many, especially beginners, even a 250 delivers a thrust that knocks you on your backend.
The 125cc 2-stroke dirt bike (yes, we know about the 4-stroke 125 but those exist more for younger riders on trails) not only tempers the throttle, allowing anyone wishing to ride quite a bit of fun, but the pros sometimes return to their roots and give this little guy a run for its money to hone lost skills they can transfer over to the big bike and rip a faster lap.
Like all dirt bikes though, the oft asked question we get is what's the top speed of a 125? A tough answer, sort of. Many factors influence how fast a 125cc dirt bike travels including the bike (stock or aftermarket parts), the rider, soil type and gearing ratio.
What is a 125cc Dirt Bike?
Of course, you know what the 125 means but for those looking to get into the sport (or hobby) and perhaps think the number refers to a model, the 125 or 125cc dirt bike refers to the engine size. In more technical terms, it means the engine's displacement, or total volume of all the engine's cylinders, measured in cubic centimeters (cc).
A 125cc dirt bike delivers about half the power and torque of a 250 and much more less than a 450 dirt bike. However, many riders adapt to the 125 and pros, as stated earlier, often fall back to training on the smaller bore engine because of a balance of power and maneuverability.
In short, a 125 offers some of the most fun you can have on a dirt bike without the speed and complexity of the larger bikes that lead many into eating a mouthful of dirt. The 125 class used to represent the "lites" class in Supercross and Motocross, replaced by the 250 class, which gave way to the 450 class, but most regional race tracks feature a 125 class series that fills the gate.
You can scroll below for the answer but you'll miss all the good stuff because many factors influence how fast a 125cc dirt bike travels. For example, ride one on pavement, expect to haul the mail, but transition over to a rough MX track and you'll drop to a snail's pace.
Factors Influencing the Speed of a 125
Dirt bike manufacturers optimize their dirt bikes for acceleration (gatedrop) and torque (gnarly off-road conditions) but not for smooth, paved straight rhythms. Therefore, the engine design and its power output play a crucial role in determining the bike's top speed. A 125cc dirt bike typically produces between 15 to 35 horsepower (HP), depending on the model, year and aftermarket modifications. The higher the horsepower, the faster the bike's potential, however, unlike a street bike, a dirt bike uses more torque and acceleration to handle off-road conditions, not for achieving high top speeds on straightaways.
We once wrote about how to drop the weight of a dirt bike. One of our suggestions was to hit the bathroom before the race. Pee in a cup and weigh it. You'll be surprised how many pounds you lose when emptying your bladder (and another bodily function.) At any rate, a rider's weight affects how fast a 125cc runs. A 200 lb person will not achieve the same top speed as someone weighing 50 lbs less.
Both riders can help their top speed cause by streamlining their body for better wind resistance, but in reality when it comes to rough terrain you probably won't get much result here.
By the way, what goes for you goes for your bike. You want to go faster? Lesson the load on your ride by replacing stock with lighter aftermarket parts which also (usually) perform better in both torque, acceleration and top speed. Most riders waste little time replacing the stock exhaust system on their dirt bikes resulting in immediate weight loss and power gains. A new clutch helps shed more weight and new handlebars and wheels help lessen the load.
Though usually illegal in sanctioned racing, a bigger bore adds a lot more power and helps push the boundaries on maximum speed.
Lastly, you can tweak the gearing ratio. Add a front sprocket with more teeth or a rear sprocket with less teeth to enjoy more top speed, just don't expect to get there very fast. This doesn't help much in racing when you need that balance between faster acceleration and top speed. Read The chat with an expert.Ultimate Dirt Bike Sprocket & Gearing Guide for more information.
Remember, aftermarket modifications can affect the handling and reliability of a dirt bike while turning your ride into a slick moving machine you can't handle. But appropriate training teaches you to go slow before you can go faster so with patience you might reach top speeds sooner than expected.
By far. terrain influences the top speed of any dirt bike the most. The rougher the track or trail the slower you go, even when pinned. Weather, too, plays a role especially when it rains and strong head winds might slow you down but hardly a usual occurrence. Temperature and altitude also contribute to engine performance and if you don't know how to adjust the air-to-fuel ratio your top speed suffers.
Some riders, though, get their kicks on Route 66 with a dirt bike approved for travel on public roads which means hitting the pinnacle in available top speed on paved roads.
125cc Dirt Bike Top Speed
Thanks for sticking it out. We have to write something to make this article worth posting otherwise we'd simply have a one sentence blog (which you may prefer) or we could dumb ourselves down and drop a quick answer on social media.
A 125cc dirt bike generally hits a top speed of 60 mph. Consider this a top speed when racing Motocross or riding trails on a hardpack straightaway - the ideal setting for a dirt bike. However, if you must, on paved roads expect to hit close to 70 mph.
Not fast enough? Kick it up a notch with a 250. Too fast? Well, adults might have a hard time going much lower but a 110 with some modifications might end up being your favorite toy.
