Choosing a Dirt Bike

The internal combustion engine revolutionized the way humans travel. Along with the invention of cars came the single-cylinder engine, and with that came dirt bikes and 2 stroke and 4 stroke engines.

Before knowing the difference between the two you need to know how the typical engine works, for example, the one in your car. Engines run on cycles, in the engine in your car the piston strokes 4 times every cycle of the engine. All 4 strokes of the piston have different names.

The first stroke is called the intake stroke, the engine takes in gas, oil, and air (gas for spark, oil for lubricant). The second stroke is the compression stroke, the gas, air, and oil is compressed into the cylinder. The third stroke is called the power stroke, this is when the spark plug sparks which explodes the gas and air mix forcing the piston down. Finally, the fourth stroke is called the exhaust stroke, this is when the piston comes back up into the cylinder forcing all of the gasses from the explosion out of the exhaust pipe. 

Now back to dirt bikes, the 4 stroke engine works exactly the same as your car does because your car is a 4 stroke. The 2 stroke engine does not. Instead of 4 piston strokes for every engine cycle, the 2 stroke has two. In the 2 stroke engine, the first stroke is the power stroke and the compression stroke. The second stroke is the intake and exhaust stroke. Because there are only 2 strokes per cycle, there are no valves in a 2 stroke engine, which means two-stroke engines mix oil with their gas.

How does this affect the performance of the dirt bikes? In a two-stroke there is no dedicated exhaust stroke so the exhaust pipe has an expansion chamber. When the compression stroke takes place, gas pushed out in the exhaust stroke (because the intake and exhaust strokes are the same) is forced back into the engine along with air causing what is called a power band. When the power band happens, it gives the engine a bigger spark, which gives the piston a hard push, which gives the engine more power.

Both engines have pros and cons. A 2 stroke will require more maintenance because the oil is burned with the gas, while a 4 stroke won’t, but 4 stroke bikes wont be as responsive when you give them gas because they have to make an extra 2 cycles before the power stroke.

So what bike should you choose? It really depends on the kind of person you are. Some people like to go fast with little power, and slow with a lot of power. If you want to ride on a motocross track you will want a 2 stroke, but for trails a 4 stroke is the way to go. So it really all comes down the question, how do you like to ride?