Two Stroke vs. Four Stroke Motorcycle Engines

If you want to know what kind of bike engine fits your needs, you need to know how a two-stroke differs from a four-stroke.
2t vs 4T debate 9 photos
Photo: KTM/autoevolution
2T vs 4T2T vs 4T2T vs 4T2T vs 4T2T vs 4T2T vs 4T2T vs 4TV16 two-stroke locomotive engine
Each of them has advantages and disadvantages. But you can't, or shouldn't, say that one is better than the other. They are just different.

Two-stroke working principle

In 1881, the Scottish engineer Dugald Clerk patented a two-stroke engine, but only in 1908 did this type of power unit become practical thanks to the Yorkshireman Alfred Angas Scott, who used them for water-cooled motorcycles.

A two-stroke cylinder produces an explosion on every rotation. When the piston moves towards the top dead center, the end of the exhaust and the compression happen. After it reaches the end of the upward movement, the spark plug ignites the explosion. On its way to the bottom dead center, the exhaust and the intake begin simultaneously.

Pros and cons of a 2T

This kind of engine has the advantage of fewer moving parts. Due to that, it's easier to repair such a powerplant. In addition, since the fuel is mixed with the lubricant, it doesn't even feature an oil pump or filter. Lastly, it has better specific power than a four-stroke engine.

Moreover, since it has fewer moving parts, it has lower inertia, meaning it can start and rev faster than a 4T. It is easy to maintain and also induces a lower gyroscopic movement to the bike it's installed, meaning that the rider can shift direction quickly. That's why some experts recommend it for hard-enduro usage.

2T vs 4T
Photo: autoevolution
On the other hand, even if it provides a smaller power band. That is the range of revolutions per minute where the engine produces enough grunt to move the bike. To keep it there, the rider has to use the clutch and the gearbox more often.

Four-stroke working principle

The first four-stroke motor was created by Nikolaus August Otto based on an 1860 engine created by the Frenchman Etienne Lenoir. But it took him another 14 years of research until the German engineer created the first fully functional 4T powerplant. And this is why you might meet these types of engines known as "Otto engines." Nevertheless, the "T" comes from the German "Takt," meaning stroke.

Here, things are somehow more complicated but easier to understand. Each piston gets a spark every other rotation. There is a time for everything: air and fuel mixture admission on the first downward stroke. On the second stroke, the upward movement compresses the mixture, which is then ignited when the piston is about to reach the top dead center. After the explosion, the piston is moved downward to the bottom dead center in the third stroke. The final stroke is when the piston moves up again, expelling the gasses resulting from the explosion.

2T vs 4T
Photo: diagrams

Pros and cons of a four-stroke

Even though it is heavier than a two-stroke engine, its higher inertia has a few advantages. It has fewer vibrations and offers a broader power band. As a result, the rider can use the same gear for a wider speed band, and they don't need to change gears too often, use the clutch, or modulate the throttle just to keep the bike going.

Another advantage of the heavier machine is that a bike fitted with such an engine is more stable at higher speeds, even while off-roading. Its stability made it a preferred choice for many riders. It is also used by most road bikes. From a technical point of view, since it uses a separate lubrication system, these four-stroke engines are more reliable than two-stroke ones.

In the downturn, it is more difficult to avoid an obstacle at the last moment since it has higher gyroscopic inertia. Also, since it provides half the explosions of a two-stroke engine, its specific power is higher. For instance, a 450 cc 4T is comparable in terms of power to a 250 cc 2T.


Since two-stroke engines are more polluting, they were banned for most street motorcycles. Still, they are used on lighter applications such as lawnmowers, generators, or go-karts. Still, there are a few bikemakers that never stopped developing them, such as KTM.

V16 two\-stroke locomotive engine
Photo: SoulRider.222/Flickr
In addition, these two-stroke powerplants are ideal for diesel fuel. This is why many heavy machines are using them. There are many power stations, tanks, and ships still making use of the two-stroke units. Moreover, since diesel fuel is greasier than gasoline, that makes it more suitable for these kinds of applications.

In terms of sound, both produce the same level of decibels but with a pitch tone for the two-stroke ones, which is more annoying. Still, a four-stroke bike sends its sound to longer distances but with a lower tune.

At the end of the day, both engines are good in their field of activity. But still, if you are using your bike on the street, you should stick with a four-stroke. If not for something else, at least for the environment's sake.

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