2-stroke vs 4-stroke: Generally speaking, there are two different types of dirt bike engines. The two-stroke and the four-stroke. If you are familiar with how engines work, a two-stroke has two “strokes” that the piston makes for a complete power cycle. A four-stroke makes four “strokes” of the piston for a complete power cycle. The main difference between the two is how quickly the power is delivered. Because of this ability to deliver more power in less time, a smaller displacement two-stroke engine generally delivers more power than the same sized four-stroke engine. The good of this is obviously: more power in a smaller engine. The bad: power delivery can often be aggressive and difficult to control and tune.
The main advantage of a two-stroke is that it has a high power to weight ratio. Most motocross motorcycles with two-stroke engines have a specific power band where most of the power is delivered. Because of this power band, most two-strokes can be difficult to control when learning because it takes a lot of clutch and shifting manipulation to keep the motorcycle in the power band. Motocross two-strokes are known for having a lot of top end power. Meaning once you get into the high RPM range is when the bike makes most of its power. Modern enduro two-stroke models and higher displacement 2-strokes tend to have a milder power delivery with better power consistency throughout the RPM range, similar to a four-stroke, making it easier for smooth riding and a bit simpler for beginners to learn. Two-strokes are very common for enduro riding mostly because of their reduced weight with high power delivery when needed.
The main advantage of a four-stroke is that it has consistent, smooth power delivery throughout the RPM range, not requiring beginner riders the need to shift and use the clutch as much to keep the bike in the power band. Modern four-strokes also have fuel injection and an engine control module (ECM), making them very tunable to different types of power delivery. When you are first learning, you likely will not utilize the tunability functions, but it is good to know they’re available. Some modern enduro two-strokes can have these features as well, however it is only offered by a few manufacturers at this time. Four-strokes are most common for full-sized motocross bikes, however there is still a large number of two-stroke motocross bikes around as well. Most motocross race series have two-stroke specific classes. Four-strokes tend to be heavier as far as power to weight ratio goes, but they do make up for it with the amount of technology, ease of control, and power delivery offered in modern day motocross racing. For Enduro riding and racing, especially for more advanced riders, four-strokes are less common because they are heavier, overheat easier, and stall easier in technical terrain. They are also more difficult to get moving from a stop as opposed to a two-stroke, which doesn’t mean much for motocross riding on a track but when you are stopped in some technical terrain and have to get going again on a steep trail, it is severely noticeable.
2-Stroke
Pros | Cons |
High power to weight ratio | Must mix oil in gas |
Does not overheat very easy | Difficult for beginners to control |
Suspension can be lowered more and valved softer than a 4-stroke to accommodate a smaller rider | Motocross models lack modern technological advances |
4-Stroke
Pros | Cons |
Modern engine technology such as fuel injection (faster throttle response, can take to different elevations without needing adjustment) with programmable ECM. | Lower power to weight ratio (compared to a two-stroke) |
Predictable and consistent power delivery throughout the RPM range | Generally will not be able to soften or lower the suspension as much as a two-stroke for smaller riders |
Easier for a beginner to learn | Easier to overheat and stall on stop-and-go terrain |
When choosing the amount of power for a full-sized dirt bike, generally, there are two tiers. The “lites” bikes include 250cc four-stroke and 125cc two-stroke. The premier bikes would be 450cc four-stroke and 250cc two-stroke. Remember, a smaller displacement two-stroke can make as much power as a larger displacement four-stroke. In motocross, due to the popularity of four-strokes, the classes are simply named 450 and 250, even though the equivalent of a 250cc four-stroke is only 125cc two-stroke and the equivalent of a 450cc four-stroke is only 250cc two-stroke. Many non-professional race programs allow riders to ride a 250cc two-stroke in the lites despite its power advantage, mostly due to the older technology and difficulty to ride at the same level as a 450cc four-stroke. Enduro and hare scrambles often split the two tiers as OPEN and 250. Open class can be any displacement whereas 250 is obviously capped at 250cc regardless of two-stroke or four-stroke.
For enduro bikes, the 300cc two-stroke and 150cc two-stroke are popular for modern models due to technology advances that allow for a larger displacement two-stroke to have more power with less vibration, smooth power delivery, and lightweight design.
Lites | Premier |
125cc 2-Stroke (Motocross) | 250cc 2-Stroke (Motocross) |
250cc 4-Stroke (Motocross) | 450cc 4-Stroke (Motocross) |
150cc 2-Stroke (Enduro) | 300cc 2-Stroke (Enduro) |
Another notable difference between the four-stroke and two-stroke is that a two-stroke requires the rider to mix special two-stroke oil into their gas at a certain ratio before fueling up the bike. There are a few modern two-stroke models that are oil injected, meaning there is a separate reservoir for the engine oil and the bike mixes the oil and gas itself as it consumes fuel. Four-strokes have an engine oil filter, and the rider must perform regular oil changes at certain hour intervals to maintain fresh engine oil free from dirt and debris, however no oil is mixed with the gas. Two-strokes also have oil that lubricates the clutch and transmission gears. This oil also must be changed but less often than a four-stroke engine oil change and does not have an engine oil filter. Four strokes use the engine oil to lubricate the clutch and transmission gears as well so no additional oil changes besides the engine oil changes are required. Generally speaking, a four-stroke will need the engine valves to be adjusted (preferably by a professional but you can do it yourself) either once a year or every 20 hours and a 2-stroke will need a new top-end (piston & rings) about every 20-40 hours.
2-stroke engines are simpler, so engine rebuilds are quite a bit easier to do. After owning both types of bikes, I'd say they are about equal in day-to-day maintenance, as long as you stay on top of it.
So . . . 2-stroke or 4-stroke? There are so many elements that factor into determining which is better, and every rider is different. The rider's weight, height, age, riding style, and skill level all factor into which engine type is best, so don't fall victim to the black and white style of thinking that one is better than the other. Both engine types have their advantages and disadvantages depending on the rider.