Two Stroke vs Four Stroke Dirt Bikes: What's the Difference?

Two-stroke or four-stroke? For people who don't know, it's like asking them about the difference between brown mustard and Dijon (both are essentially made from the same stuff, but one has more of a kick).

Whether a two-stroke or a four-stroke dirt bike is a better choice largely depends on how you ride it. The terms two-stroke and four-stroke essentially tell us how the engine functions. If you're just a beginner on a dirt bike, knowing the difference between the two is a good place to start.

Two-Stroke Dirt Bikes

In a two-stroke engine, the spark plug in the cylinder fires every time the crankshaft makes a turn. An internal combustion engine pulls in fuel and air, compresses it, then the spark plug initiates combustion and the byproducts are pushed out of the cylinder through the exhaust. When combustion or down-stroke in the engine ends, another cycle of compression begins. Intake and exhaust happen at the same time.

There are advantages to the two-stroke setup, including a lighter engine with fewer moving parts. The engines can be more compact and easier to maintain, but the need for maintenance can be more frequent. Two-stroke setups can mean greater speed, but it also means the bike requires more shifting because the power band — the range of RPMs where the engine operates at its peak — is more narrow.

Four-Stroke Dirt Bikes

The four-stroke machine is a bit more complex. Here, it takes two turns of the crankshaft for the cylinder to go through all four cycles: intake, compression, ignition, exhaust. The spark plug fires every other turn of the crankshaft as compression occurs, and the other upstroke of the piston pushes byproducts of combustion out through the exhaust.

There are advantages to the four-stroke engine setup. First, the power band is a bit broader, meaning there's less shifting. Four stroke engines also require less maintenance. However, four-stroke engines are heavier, and repairs can be costlier. On balance, riders who have experience with both often say that despite the lack of throttle responsiveness and top-end speed, four-stroke engines are easier to ride because of their steady power and easy control.

Two-Stroke vs. Four-Stroke Power

In the two-stroke engine, you're cutting the amount of work the engine does in half. As a result, it's easier to get power from the two-stroke. 

A 125cc two-stroke dirt bike, for example, puts down about the same power as a 250cc four-stroke dirt bike. And while the two have the same power, that power will come with a lot more kick on the lighter, 125cc machine.