Dirt Bike Engine Classes

The engine size in the model name gives us a starting point for understanding how big and powerful a particular bike is, but it takes more background knowledge on the types of bikes that are on the market to fully understand what each model is for. The models aimed at a particular market segment tend to share a common displacement, resulting in “market classes” of bikes that share common design specifications. Being familiar with these classes will help you understand what options are available, as well as give you a framework for classifying the different model names as you become familiar with them.

Here are the common engine classes and what types of bikes they define.

This is the smallest engine displacement available in the gas-powered lineup.  These bikes are intended for the smallest riders, approximately 4-7 years of age.  The traditional starter 50cc bikes included the two-stroke Yamaha PW50 and Honda XR50, both of which were reliable, simple, universally adored starter bikes that are still passed around and loved today.  Four-stroke offerings incuding the Yamaha TT-R50 and Honda CRF50 have replaced the PW and XR in recent years.

Most 50cc bikes are mellow starter bikes, but a select few—like the KTM 50 SX and Husqvarna TC 50—are intended for racing motocross and are taller and much more powerful than the beginner bikes. These race bikes are not intended for pure beginners and would generally be a next step for a rider graduating from a 50cc beginner bike who is getting started in racing.

Motocross bikes for introducing kids from 6-10 to the world of racing.  These bikes are all 2-strokes and are typically suited to kids who've already mastered a 50cc or an electric bike.

This is a much less common engine class, currently dominated by the less expensive offerings from Chinese manufacturers.  In the past, bikes like the CRF70F existed, offering a mellow trail bike slightly larger in stature than their 50cc counterparts.

The 85cc class is almost exclusively small-wheeled, two-stroke motocross race bikes for kids from 10-13 years old. The 85 is usually the next step up from a 65 for moto kids.

This is a mixed grouping.  Historically, air-cooled, four-stroke bikes like the XR100 and CRF100 offered approachable, easy to ride trail mounts for kids and small adults who are getting into riding.  These models have since been discontinued and replaced by 125cc trail bikes.  Today, the KX100—a larger alternative to an 85cc two- stroke motocross race bike for pre-teens—is re-defining the 100cc class.

Today’s 110cc class is comprised of air-cooled, four-stroke trail bikes that have replaced the 70/80cc trail bikes of past decades. These bikes are targeted at kids from 7-11 years old. Most adults will find these bikes far too small to make their permanent mounts, but you’ll frequently see adults buzzing around the pits at races on machines of this size—they are also known as “pit bikes” for this reason.

These bikes are the step up from the 110cc class and are geared toward teens and smaller adult riders who trail ride—these are not race bikes. The 125 four-stroke is a very manageable, mellow machine with smooth power and soft suspension. Some 125’s come in either a small-wheel or big-wheel variation. Big-wheel versions have higher seats and longer wheelbases and are suited for taller riders.

The 125cc motocross bike class rose to popularity in the 1960’s and existed as a professional class until 2006, when the dominance of 250cc four-stroke motocross bikes pushed the 125cc class out of the pro circuit. Since then, it has been a staple of youth motocross, serving as a rite of passage to the 250cc bikes. 125cc two-strokes rev high and have a narrow powerband and snappy power delivery. Riding them well requires keeping the engine speed up and shifting frequently to stay “on the pipe.” 125s are challenging to ride, but they are known for teaching riders good habits and superior riding skills.

There are also a handful of 125cc two-stroke enduro bikes on the market, mostly offered by European manufacturers. These machines are sprung softer and have a more linear power delivery than the motocross 125s, but they’re still small-bores and have to be ridden aggressively and with a lot of shifting. They lack the torque needed for really technical offroad riding, but they’re competitive in higher-speed woods racing.

The two most well-known 150cc four-stroke models are the Honda CRF150F and the CRF150R. The CRF150F is a mellow trail bike designed for teenagers or small adults, but it was discontinued in 2017 and replaced by a 125cc model. The CRF150R, however, remains on the market today. The “R” mode is the motocross race designation, and the CRF150R is a liquid-cooled, quick-revving performance bike designed for the track. It is not a beginner bike.

The 150cc two-stroke has emerged as a new small-bore offering for woods racing, replacing the 200cc two-strokes in certain manufacturer’s lineups. Although a 150 has limited torque compared to the 250/300cc bikes and must be ridden aggressively to stay in the powerband, they are lightweight and nimble and are popular with smaller riders or teens. Currently, the only two bikes in this class are made by KTM/Husqvarna.

The traditional small-bore woods bike, the 200cc two-stroke is a compromise between the light weight of a 125 and the torque of a 250/300. They are very versatile and fun machines, requiring more aggressive shifting and clutching than a 250/300, but while being easier to ride and more forgiving than a 125. A 200 is both a great starter bike for a confident adult (the power is generally quick-revving but not hard-hitting), or a permanent woods racing machine for a lighter-than-average rider. They are also a hit with the stockier sort who want a fun and lightweight play bike.

Only three models make up the 230cc four-stroke trail bike class: the Yamaha TT-R230, the Honda CRF230, and the Kawasaki KLX230R. The CRF230 was discontinued in 2019 and succeeded by a 250cc version, but the TT-R and the KLX remain on the market as of 2024. The 230 is a simple, reliable, easy to ride trail bike for beginner adults on the smaller side.

The bulk of the 250cc bikes on the market are the motocross race models. Being the penultimate competitive class in professional motocross racing, the 250cc mx racer is a staple, and virtually every manufacturer makes one. These machines are fast and make impressive power that is generally sufficient to carry all but the heftiest of riders or hit the biggest triples. While they are not “entry-level” bikes, per se, a 250cc is generally the most-recommended motocross bike for the adult who is getting into motocross, and is the bike that most riders will stick with. (A 125cc is more challenging to ride, and a 450 is a LOT of bike and is not needed except by especially hefty riders.)

There are also a range of 250cc four-stroke woods bikes, in trims from the entry-level CRF250F trail bike up to the race-ready Yamaha YZ250FX. An growing trend is for manufacturers who produce enduro bikes to offer “cross-country” racing models: variants of their 250cc motocross bikes that feature 18” rear wheels, different gearing, different ignition mapping, softer suspensions, and larger fuel tanks.

Following the same complicated split is the two-stroke side of the 250 class. As with the 250 four-strokes, we see motocross, cross-country, and enduro offerings. A 250cc two-stroke is a strong powerplant, and none of these bikes would be suitable for a beginner.

The two-stroke 250 motocrosser was the premier race bike until the four-stroke supplanted it, but they are still widely available and popular with racers at the non- professional level. These machines are hard-hitting and incredibly powerful. When raced at the top level, 250 two-strokes are pitted against the 450 four-strokes.

The enduro 250 is a very popular mount for woods racing and hard enduro, having a slightly faster-revving and lighter character than it’s very similar 300cc counterpart.

Since 250s exist for so many different market segments, it can be hard to guess at a bike’s specs just by knowing it’s a 250. Being familiar with the individual models and their purposes is necessary to ascertain the purpose of each bike in this market class.

Virtually all modern 300cc dirt bikes are two-strokes, with one or two exceptions. Aside from motocross offerings from KTM and TM, the rest of the 300cc two-strokes on the market are enduro and cross-country bikes. The 300 is the top choice for hard enduro riders, where the torquey and stall-resistant powerplant shines. A 300 enduro bike is very similar to its 250 counterpart, but it is slightly slower-revving and has more low-end grunt. With a few exceptions—like the Beta X-Trainer—that are relatively mellow, a 300 is still a big bore bike with a lot of power on tap that is best suited to intermediate and advanced riders.

Following the same trend at the 300cc two-strokes, the 350 four-stroke bikes are all enduro or cross-country models, aside from motocross models produced by KTM and Husqvarna. The 350cc four-stroke is a relatively new invention, offering more power than the more traditional 250cc four-stroke but being more agile and suited to singletrack than a bigger bore (400cc+) four-banger. These bikes continue to grow in popularity on the woods racing scene.

The 450cc class is a four-stroke, performance machine class primarily made up of motocross and cross-country models (a 450 is too powerful to be ridden effectively in slow and technical terrain, so enduro models are not popular). This is the premier moto racer that riders in the top professional classes ride. A modern 450 four-stroke makes a whopping 50+ horsepower and is a handful of a machine for all but advanced riders. They are also highly tuned and require meticulous maintenance—these are serious machines, not play bikes.

Although there are no 500cc two-strokes currently being produced (and haven’t been for almost 20 years), the iconic 500s—including the Honda CR500, Kawasaki KX500, and 501 Maico—are legendary. Although they produce about the same peak horsepower as today’s 450s, their typical two-stroke power delivery made the machine intolerable to all but the boldest of riders. Although they were never a practical success, the 500 lives on as a symbol of ultimate power.

The big-bore thumpers. Most of the bikes in this small class are enduro machines with linear power delivery and ridiculous amount of torque. Because the bikes are a bit of a handful on tight and slow trails, they are best suited to more open, higher-speed trails, and they are especially appreciated at higher elevation where power is robbed by the decreased air density. They also make good dual sport conversions, and a number of factory-plated dual sports are in this displacement range.