When considering a 2-stroke vs 4-stroke dirt bike, start by assessing how you plan to ride the bike.
For most riders, that means riding single-track trails and competing in the occasional hare scramble near home. You may also tear up the gravel roads or fields in your area, too. For you, riding dirt bikes is a passion, but not a profession.
For some, it means competing in sanctioned Motocross or Supercross races. While you may also ride the trails near home, your focus is on improving your skills so you can earn more podium finishes and build your racing career.
4-stroke dirt bike benefits
A 450-cc four-stroke dirt bike, like a Honda CRF450 or Kawasaki KX450, is the top choice for riders competing in sanctioned races.
Big power and torque
Four-strokes make massive power and torque given their relatively small engines. A professional rider on a 4-stroke dirt bike can nail a complicated triple jump with just a 10-foot runup. You not only need skill to pull off that feat, you need the kind of stump-pulling torque only a 4-stroke dirt bike offers.
Given their design, 4-strokes emit less exhaust emissions than 2-stroke dirt bikes. A 2-stroke burns the oil during combustion by design, which increases smoke (particularly if using a low-quality oil) and emissions.
250-cc 4-stroke bikes are also popular, especially for weekend warriors and beginners. They’re lighter, easier to handle and less expensive.
4-stroke dirt bike challenges
All that power and torque comes with a price, however, and it’s increased time and money spent on maintenance.
A typical 450-cc four-stroke makes about 50 horsepower from an engine that’s about the same size as a lawnmower engine. That’s a ton of stress on one relatively small piston.
To reduce drag and maximize power, the piston in a four-stroke dirt bike usually has a shorter skirt than what you’re used to seeing. Because of this, the piston wants to rock back and forth in the cylinder. This can lead to wear, which shrinks the piston. Eventually, the piston can turn sideways and cause thousands of dollars of damage.
Adding to the challenge, most bikes only hold about a quart of oil. One quart of oil has to handle the massive power (re. stress) of the engine.
Revving the bike to 10,000 rpm as you chase glory on the racetrack increases heat, which causes oil to break down faster. Oil sump temperature can surpass 300ºF (149°C), causing the oil to break down and fail to protect the engine, leading to wear.
That’s why most manufacturers recommend rebuilding the top end of the engine every 50 hours or so. This adds up fast if you ride a lot.
Plan on budgeting at least $500 for every rebuild.
2-stroke dirt bike dominance
Two-strokes were popular back in the ’70s and ’80s. Pound-for-pound, they make more power than 4-stroke bikes.
The reason lies in how an engine works.
An internal combustion engine completes four stages during each combustion cycle: intake, compression, power and exhaust.
The engine draws air/fuel into the cylinder (intake), compresses it in preparation for combustion, ignites it via the spark plug to produce the explosion that powers the piston and, finally, exhausts the spent gases out the exhaust valve.
A 2-stroke engine requires only one complete crankshaft revolution to complete the four stages of combustion. A 4-stroke engine requires two crankshaft revolutions.
Some quick math reveals that, in a 2-stroke, you get power with every turn of the crankshaft. But, in a 4-stroke, you only get power every other turn of the crankshaft.
This advantage explains why a 250-cc 2-stroke engine makes more power than a 4-stroke of the same size.
Regulations doomed early 2-strokes
Our decision seems obvious now: get a 2-stroke bike.
If only it were that simple. As noted earlier, 2-stroke engines burn oil as part of combustion. This increases exhaust emissions, something that ran afoul of our developing environmental awareness of the ’70s and ’80s.
Soon, increasingly strict environmental regulations made it more economically attractive to develop 4-stroke engines, slowing 2-stroke dirt bike sales.
In 1998, the AMA ruled that professional riders could compete on 450-cc 4-stroke dirt bikes against 250-cc 2-stroke bikes to even the power advantage. The pros switched to 4-strokes, the public followed and 2-stroke sales seemed all but doomed.
The resurgence of 2-stroke dirt bikes
Today, however, 2-stroke dirt bikes are making a comeback. New technologies have reduced exhaust emissions while increasing power. While a 2-stroke will never offer the torque of a 4-stroke, they come close enough for most weekend riders.
Not only that, but they’re lighter and tend to be easier to handle, which makes them great for beginners.
Older 2-strokes require riders to rev the engine to make any power. This doesn’t lend itself to navigating tight corners or obstacles on a single-track trail deep in the woods.
Advancements in exhaust-port and power-valve design now allow you to effectively ride a 2-stroke at lower rpm, which makes them ideal in wooded areas.
In addition, 2-stroke bikes require less maintenance than most 4-strokes, saving you time and money.
Two-stroke dirt bike challenges
As said, 2-strokes lack the stump-pulling low-end torque of a 4-stroke dirt bike, particularly a 450. This lack of immediate torque once you twist the throttle can affect your ability to execute certain riding technique. It also puts you at a disadvantage in a competitive situation.
So, which is right for me?
Ultimately, you have to decide which bike is the best fit for your riding style and ability.
If you’re racing professionally (or hope to someday), lean toward the 4-stroke. The same holds for hardcore riders who want maximum power and torque, but who don’t mind rebuilding their bike every 50 hours to the tune of $500.
For weekend warriors and beginners, a newer 250-cc 2-stroke offers the ridability of most 4-strokes, minus some torque. Plus, they’re less expensive to maintain. A 250-cc 4-stroke is also a great option since it’s less expensive, lighter and easier to ride for a beginner.
Whichever bike you choose, use a good oil
Regardless how you answer the 2 stroke vs 4 stroke dirt bike question, don’t cheap out on motor oil.
As said, only about one quart of oil protects your 4-stroke engine against wear. That thin layer of oil prevents the piston from scuffing against the cylinder wall and the bearings from wearing out and failing.
Plus, with sump temperatures up to 300ºF (149ºC) or more, the oil has to be capable of withstanding intense heat and maintaining protection.
AMSOIL Synthetic Dirt Bike Oil delivers. Its superior friction-durability properties help minimize clutch slippage, fade and chatter, giving riders consistent clutch feel during takeoffs or when maneuvering around obstacles on the trail.
For those who opt for a 2-stroke, we recommend AMSOIL DOMINATOR Synthetic 2-Stroke Racing Oil.
- Excellent film strength for high-heat, high-rpm motors
- Anti-friction formula for maximum power
- Burns clean; helps prevent ring sticking and plug fouling
- Protects coated and non-coated racing pistons